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-rw-r--r--LICENSE15
-rw-r--r--Makefile12
-rw-r--r--README.adoc49
-rw-r--r--bfc-amd64-linux.c723
-rw-r--r--interpreters/Makefile14
-rw-r--r--interpreters/README.adoc15
-rw-r--r--interpreters/bf-faster-loops.c151
-rw-r--r--interpreters/bf-jit-opt.c495
-rw-r--r--interpreters/bf-jit-unsafe-opt.c617
-rw-r--r--interpreters/bf-jit-unsafe.c495
-rw-r--r--interpreters/bf-jit.c327
-rw-r--r--interpreters/bf-optimizing.c213
-rw-r--r--interpreters/bf.c160
13 files changed, 3286 insertions, 0 deletions
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..ce263ae
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,15 @@
+ Copyright (c) 2016, Přemysl Janouch <p.janouch@gmail.com>
+ All rights reserved.
+
+ Permission to use, copy, modify, and/or distribute this software for any
+ purpose with or without fee is hereby granted, provided that the above
+ copyright notice and this permission notice appear in all copies.
+
+ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+ SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+ OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+ CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..5bb5db1
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,12 @@
+# All we need is C99 and POSIX, which this should make available
+CFLAGS = -std=gnu99
+NAMES = bfc-amd64-linux
+
+all: $(NAMES)
+
+%: %.c
+ $(CC) $(CPPFLAGS) $(CFLAGS) $< -o $@
+clean:
+ rm -f $(NAMES)
+
+.PHONY: all clean
diff --git a/README.adoc b/README.adoc
new file mode 100644
index 0000000..660c38c
--- /dev/null
+++ b/README.adoc
@@ -0,0 +1,49 @@
+bfc
+===
+
+'bfc' is a small, fast, self-contained, optimizing Brainfuck compiler for Linux
+on Intel x86-64.
+
+Also included are several interpreters in various states of sophistication that
+document my progress as I was writing this, from the simplest approach to an
+optimizing JIT compiler.
+
+It's pretty easy to retarget the compiler, it just means redoing half the work.
+The compiler itself is platform agnostic.
+
+Building
+--------
+Build dependencies: a C99 compiler +
+Runtime dependencies: Linux
+
+ $ git clone https://github.com/pjanouch/bfc.git
+ $ cd bfc
+ $ make
+
+To obtain dumps of the intermediate representation, compile with `-DDEBUG`:
+
+ $ make CPPFLAGS=-DDEBUG
+
+Usage
+-----
+
+ ./bfc-amd64-linux [INPUT-FILE] [OUTPUT-FILE]
+
+When no input file is specified, stdin is used. Similarly, the default output
+filename is a.out. The resulting file can be run on the target platform.
+
+Contributing and Support
+------------------------
+Use this project's GitHub to report any bugs, request features, or submit pull
+requests. If you want to discuss this project, or maybe just hang out with
+the developer, feel free to join me at irc://irc.janouch.name, channel #dev.
+
+License
+-------
+'bfc' is written by Přemysl Janouch <p.janouch@gmail.com>.
+
+You may use the software under the terms of the ISC license, the text of which
+is included within the package, or, at your option, you may relicense the work
+under the MIT or the Modified BSD License, as listed at the following site:
+
+http://www.gnu.org/licenses/license-list.html
diff --git a/bfc-amd64-linux.c b/bfc-amd64-linux.c
new file mode 100644
index 0000000..039e224
--- /dev/null
+++ b/bfc-amd64-linux.c
@@ -0,0 +1,723 @@
+// This is an exercise in futility more than anything else
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <assert.h>
+#include <errno.h>
+
+#define exit_fatal(...) \
+ do { \
+ fprintf (stderr, "fatal: " __VA_ARGS__); \
+ exit (EXIT_FAILURE); \
+ } while (0)
+
+// --- Safe memory management --------------------------------------------------
+
+static void *
+xcalloc (size_t m, size_t n)
+{
+ void *p = calloc (m, n);
+ if (!p)
+ exit_fatal ("calloc: %s\n", strerror (errno));
+ return p;
+}
+
+static void *
+xrealloc (void *o, size_t n)
+{
+ void *p = realloc (o, n);
+ if (!p && n)
+ exit_fatal ("realloc: %s\n", strerror (errno));
+ return p;
+}
+
+// --- Dynamically allocated strings -------------------------------------------
+
+struct str
+{
+ char *str; ///< String data, null terminated
+ size_t alloc; ///< How many bytes are allocated
+ size_t len; ///< How long the string actually is
+};
+
+static void
+str_init (struct str *self)
+{
+ self->len = 0;
+ self->str = xcalloc (1, (self->alloc = 16));
+}
+
+static void
+str_ensure_space (struct str *self, size_t n)
+{
+ // We allocate at least one more byte for the terminating null character
+ size_t new_alloc = self->alloc;
+ while (new_alloc <= self->len + n)
+ new_alloc <<= 1;
+ if (new_alloc != self->alloc)
+ self->str = xrealloc (self->str, (self->alloc = new_alloc));
+}
+
+static void
+str_append_data (struct str *self, const void *data, size_t n)
+{
+ str_ensure_space (self, n);
+ memcpy (self->str + self->len, data, n);
+ self->str[self->len += n] = '\0';
+}
+
+static void
+str_append_c (struct str *self, char c)
+{
+ str_append_data (self, &c, 1);
+}
+
+// --- Application -------------------------------------------------------------
+
+enum command
+{
+ RIGHT, LEFT, INC, DEC, IN, OUT, BEGIN, END,
+ SET, EAT, INCACC, DECACC
+};
+
+bool grouped[] = { 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0 };
+struct instruction { enum command cmd; int offset; size_t arg; };
+#define INSTRUCTION(c, o, a) (struct instruction) { (c), (o), (a) }
+
+// - - Debugging - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+#ifdef DEBUG
+static void
+debug_dump_instruction (FILE *fp, const struct instruction *in)
+{
+ const char *name;
+ switch (in->cmd)
+ {
+ case RIGHT: name = "RIGHT "; break;
+ case LEFT: name = "LEFT "; break;
+ case INC: name = "INC "; break;
+ case DEC: name = "DEC "; break;
+ case OUT: name = "OUT "; break;
+ case IN: name = "IN "; break;
+ case BEGIN: name = "BEGIN "; break;
+ case END: name = "END "; break;
+ case SET: name = "SET "; break;
+ case EAT: name = "EAT "; break;
+ case INCACC: name = "INCACC"; break;
+ case DECACC: name = "DECACC"; break;
+ }
+ fprintf (fp, "%s %zu", name, in->arg);
+ if (in->offset != 0)
+ fprintf (fp, " [%d]", in->offset);
+ fprintf (fp, "\n");
+}
+
+static void
+debug_dump (const char *filename, struct instruction *in, size_t len)
+{
+ FILE *fp = fopen (filename, "w");
+ long indent = 0;
+ for (size_t i = 0; i < len; i++)
+ {
+ if (in[i].cmd == END)
+ indent--;
+ for (long k = 0; k < indent; k++)
+ fputs (" ", fp);
+ debug_dump_instruction (fp, &in[i]);
+ if (in[i].cmd == BEGIN)
+ indent++;
+ }
+ fclose (fp);
+}
+#else
+#define debug_dump(...)
+#endif
+
+// - - Optimization passes - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+static size_t
+optimize_assignment (struct instruction *irb, size_t irb_len)
+{
+ size_t in = 0, out = 0;
+ for (; in < irb_len; in++, out++)
+ {
+ if (in + 2 < irb_len
+ && irb[in ].cmd == BEGIN
+ && irb[in + 1].cmd == DEC && irb[in + 1].arg == 1
+ && irb[in + 2].cmd == END)
+ {
+ irb[out] = INSTRUCTION (SET, 0, 0);
+ in += 2;
+ }
+ else if (out && irb[out - 1].cmd == SET && irb[in].cmd == INC)
+ irb[--out].arg += irb[in].arg;
+ else if (out != in)
+ irb[out] = irb[in];
+ }
+ return out;
+}
+
+// Add offsets to INC/DEC/SET stuck between LEFT/RIGHT
+// and compress the LEFT/RIGHT sequences
+static size_t
+optimize_offseted_inc_dec (struct instruction *irb, size_t irb_len)
+{
+ size_t in = 0, out = 0;
+ for (in = 0, out = 0; in < irb_len; in++, out++)
+ {
+ intptr_t dir = 0;
+ if (irb[in].cmd == RIGHT)
+ dir = irb[in].arg;
+ else if (irb[in].cmd == LEFT)
+ dir = -(intptr_t) irb[in].arg;
+ else
+ {
+ irb[out] = irb[in];
+ continue;
+ }
+
+ while (in + 2 < irb_len)
+ {
+ // An immediate offset has its limits on x86-64
+ if (dir < INT8_MIN || dir > INT8_MAX)
+ break;
+
+ intptr_t diff;
+ if (irb[in + 2].cmd == RIGHT)
+ diff = irb[in + 2].arg;
+ else if (irb[in + 2].cmd == LEFT)
+ diff = -(intptr_t) irb[in + 2].arg;
+ else
+ break;
+
+ int cmd = irb[in + 1].cmd;
+ if (cmd != INC && cmd != DEC && cmd != SET)
+ break;
+
+ irb[out] = irb[in + 1];
+ irb[out].offset = dir;
+
+ dir += diff;
+ out += 1;
+ in += 2;
+ }
+
+ for (; in + 1 < irb_len; in++)
+ {
+ if (irb[in + 1].cmd == RIGHT)
+ dir += irb[in + 1].arg;
+ else if (irb[in + 1].cmd == LEFT)
+ dir -= (intptr_t) irb[in + 1].arg;
+ else
+ break;
+ }
+
+ if (!dir)
+ out--;
+ else if (dir > 0)
+ irb[out] = INSTRUCTION (RIGHT, 0, dir);
+ else
+ irb[out] = INSTRUCTION (LEFT, 0, -dir);
+ }
+ return out;
+}
+
+// Try to eliminate loops that eat a cell and add/subtract its value
+// to/from some other cell
+static size_t
+optimize_inc_dec_loops (struct instruction *irb, size_t irb_len)
+{
+ size_t in = 0, out = 0;
+ for (in = 0, out = 0; in < irb_len; in++, out++)
+ {
+ irb[out] = irb[in];
+ if (irb[in].cmd != BEGIN)
+ continue;
+
+ bool ok = false;
+ size_t count = 0;
+ for (size_t k = in + 1; k < irb_len; k++)
+ {
+ if (irb[k].cmd == END)
+ {
+ ok = true;
+ break;
+ }
+ if (irb[k].cmd != INC
+ && irb[k].cmd != DEC)
+ break;
+ count++;
+ }
+ if (!ok)
+ continue;
+
+ // Stable sort operations by their offsets, put [0] first
+ bool sorted;
+ do
+ {
+ sorted = true;
+ for (size_t k = 1; k < count; k++)
+ {
+ if (irb[in + k].offset == 0)
+ continue;
+ if (irb[in + k + 1].offset != 0
+ && irb[in + k].offset <= irb[in + k + 1].offset)
+ continue;
+
+ struct instruction tmp = irb[in + k + 1];
+ irb[in + k + 1] = irb[in + k];
+ irb[in + k] = tmp;
+ sorted = false;
+ }
+ }
+ while (!sorted);
+
+ // Abort the optimization on duplicate offsets (complication with [0])
+ for (size_t k = 1; k < count; k++)
+ if (irb[in + k].offset == irb[in + k + 1].offset)
+ ok = false;
+ // XXX: can't make the code longer either
+ for (size_t k = 1; k <= count; k++)
+ if (irb[in + k].arg != 1)
+ ok = false;
+ if (!ok
+ || irb[in + 1].cmd != DEC
+ || irb[in + 1].offset != 0)
+ continue;
+
+ int min_safe_left_offset = 0;
+ if (in > 1 && irb[in - 1].cmd == RIGHT)
+ min_safe_left_offset = -irb[in - 1].arg;
+
+ bool cond_needed_for_safety = false;
+ for (size_t k = 0; k < count; k++)
+ if (irb[in + k + 1].offset < min_safe_left_offset)
+ {
+ cond_needed_for_safety = true;
+ break;
+ }
+
+ in++;
+ if (cond_needed_for_safety)
+ out++;
+
+ irb[out] = INSTRUCTION (EAT, 0, 0);
+ for (size_t k = 1; k < count; k++)
+ irb[out + k] = INSTRUCTION (irb[in + k].cmd == INC
+ ? INCACC : DECACC, irb[in + k].offset, 0);
+
+ in += count;
+ out += count;
+
+ if (cond_needed_for_safety)
+ irb[out] = INSTRUCTION (END, 0, 0);
+ else
+ out--;
+ }
+ return out;
+}
+
+// - - Loop pairing - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+static void
+pair_loops (struct instruction *irb, size_t irb_len)
+{
+ size_t nesting = 0;
+ size_t *stack = xcalloc (sizeof *stack, irb_len);
+ for (size_t i = 0; i < irb_len; i++)
+ {
+ switch (irb[i].cmd)
+ {
+ case BEGIN:
+ stack[nesting++] = i;
+ break;
+ case END:
+ if (nesting <= 0)
+ exit_fatal ("unbalanced loops\n");
+
+ --nesting;
+ irb[stack[nesting]].arg = i + 1;
+
+ // Looping can be disabled by optimizations
+ if (irb[i].arg)
+ irb[i].arg = stack[nesting] + 1;
+ default:
+ break;
+ }
+ }
+ free (stack);
+
+ if (nesting != 0)
+ exit_fatal ("unbalanced loops\n");
+}
+
+// - - Main - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+int
+main (int argc, char *argv[])
+{
+ if (argc > 3)
+ exit_fatal ("usage: %s [INPUT-FILE]\n", argv[0]);
+
+ FILE *input_file = stdin;
+ if (argc > 1 && !(input_file = fopen (argv[1], "r")))
+ exit_fatal ("fopen: %s: %s\n", argv[1], strerror (errno));
+
+ const char *output_path = "a.out";
+ if (argc > 2)
+ output_path = argv[2];
+
+ struct str buffer;
+ str_init (&buffer);
+
+ int c;
+ while ((c = fgetc (input_file)) != EOF)
+ str_append_c (&buffer, c);
+ if (ferror (input_file))
+ exit_fatal ("can't read program\n");
+ fclose (input_file);
+
+// - - Decode, group and optimize - - - - - - - - - - - - - - - - - - - - - - -
+
+ // This is our Intermediate Representation Buffer
+ struct instruction *irb = xcalloc (sizeof *irb, buffer.len);
+ size_t irb_len = 0;
+
+ for (size_t i = 0; i < buffer.len; i++)
+ {
+ enum command cmd;
+ switch (buffer.str[i])
+ {
+ case '>': cmd = RIGHT; break;
+ case '<': cmd = LEFT; break;
+ case '+': cmd = INC; break;
+ case '-': cmd = DEC; break;
+ case '.': cmd = OUT; break;
+ case ',': cmd = IN; break;
+ case '[': cmd = BEGIN; break;
+ case ']': cmd = END; break;
+ default: continue;
+ }
+
+ // The most basic optimization is to group identical commands together
+ if (!irb_len || !grouped[cmd] || irb[irb_len - 1].cmd != cmd)
+ irb_len++;
+
+ irb[irb_len - 1].cmd = cmd;
+ irb[irb_len - 1].arg++;
+ }
+
+ debug_dump ("bf-no-opt.txt", irb, irb_len);
+ irb_len = optimize_assignment (irb, irb_len);
+ debug_dump ("bf-pre-offsets.txt", irb, irb_len);
+ irb_len = optimize_offseted_inc_dec (irb, irb_len);
+ debug_dump ("bf-pre-incdec-unloop.txt", irb, irb_len);
+ irb_len = optimize_inc_dec_loops (irb, irb_len);
+ debug_dump ("bf-optimized.txt", irb, irb_len);
+ pair_loops (irb, irb_len);
+ debug_dump ("bf-final.txt", irb, irb_len);
+
+// - - Code generation - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+ str_init (&buffer);
+ size_t *offsets = xcalloc (sizeof *offsets, irb_len + 1);
+ bool *sets_flags = xcalloc (sizeof *sets_flags, irb_len);
+
+#define CODE(x) { char t[] = x; str_append_data (&buffer, t, sizeof t - 1); }
+#define LE(v) (uint8_t[]) { v, v>>8, v>>16, v>>24, v>>32, v>>40, v>>48, v>>56 }
+#define DB(x) { uint64_t v = (x); str_append_data (&buffer, LE (v), 1); }
+#define DW(x) { uint64_t v = (x); str_append_data (&buffer, LE (v), 2); }
+#define DD(x) { uint64_t v = (x); str_append_data (&buffer, LE (v), 4); }
+#define DQ(x) { uint64_t v = (x); str_append_data (&buffer, LE (v), 8); }
+
+ enum
+ {
+ ELF_LOAD_CODE = 0x400000, // where code is loaded (usual)
+ ELF_LOAD_DATA = 0x800000 // where the tape is placed
+ };
+
+ CODE ("\xB8") DD (ELF_LOAD_DATA) // mov rax, "ELF_LOAD_DATA"
+ CODE ("\x30\xDB") // xor bl, bl
+
+ for (size_t i = 0; i < irb_len; i++)
+ {
+ offsets[i] = buffer.len;
+
+ size_t arg = irb[i].arg;
+ assert (arg <= UINT32_MAX);
+
+ int offset = irb[i].offset;
+ assert (offset <= INT8_MAX && offset >= INT8_MIN);
+
+ // Don't save what we've just loaded
+ if (irb[i].cmd == LEFT || irb[i].cmd == RIGHT)
+ if (i < 2 || i + 1 >= irb_len
+ || (irb[i - 2].cmd != LEFT && irb[i - 2].cmd != RIGHT)
+ || irb[i - 1].cmd != BEGIN
+ || irb[i + 1].cmd != END)
+ CODE ("\x88\x18") // mov [rax], bl
+
+ switch (irb[i].cmd)
+ {
+ case RIGHT:
+ // add rax, "arg" -- optimistic, no boundary checking
+ if (arg > INT8_MAX) { CODE ("\x48\x05") DD (arg) }
+ else { CODE ("\x48\x83\xC0") DB (arg) }
+ break;
+ case LEFT:
+ // sub rax, "arg" -- optimistic, no boundary checking
+ if (arg > INT8_MAX) { CODE ("\x48\x2D") DD (arg) }
+ else { CODE ("\x48\x83\xE8") DB (arg) }
+ break;
+
+ case EAT:
+ // NOTE: the kernel destroys rcx and r11 on syscalls,
+ // there must be no OUT or IN between EAT and INCACC/DECACC
+ CODE ("\x88\xD9" "\x30\xDB") // mov cl, bl; xor bl, bl
+ sets_flags[i] = true;
+ break;
+ case INCACC:
+ if (offset)
+ {
+ CODE ("\x00\x48") DB (offset) // add [rax+"offset"], cl
+ }
+ else
+ {
+ CODE ("\x00\xCB") // add bl, cl
+ sets_flags[i] = true;
+ }
+ break;
+ case DECACC:
+ if (offset)
+ {
+ CODE ("\x28\x48") DB (offset) // sub [rax+"offset"], cl
+ }
+ else
+ {
+ CODE ("\x28\xCB") // sub bl, cl
+ sets_flags[i] = true;
+ }
+ break;
+
+ case INC:
+ if (offset)
+ {
+ CODE ("\x80\x40") DB (offset) // add byte [rax+"offset"], "arg"
+ }
+ else
+ {
+ CODE ("\x80\xC3") // add bl, "arg"
+ sets_flags[i] = true;
+ }
+ DB (arg)
+ break;
+ case DEC:
+ if (offset)
+ {
+ CODE ("\x80\x68") DB (offset) // sub byte [rax+"offset"], "arg"
+ }
+ else
+ {
+ CODE ("\x80\xEB") // sub bl, "arg"
+ sets_flags[i] = true;
+ }
+ DB (arg)
+ break;
+ case SET:
+ if (offset)
+ {
+ CODE ("\xC6\x40") DB (offset) // mov byte [rax+"offset"], "arg"
+ }
+ else
+ CODE ("\xB3") // mov bl, "arg"
+ DB (arg)
+ break;
+
+ case OUT:
+ CODE ("\xE8") DD (0) // call "write"
+ break;
+ case IN:
+ CODE ("\xE8") DD (0) // call "read"
+ break;
+
+ case BEGIN:
+ // Don't test the register when the flag has been set already;
+ // this doesn't have much of an effect in practice
+ if (!i || !sets_flags[i - 1])
+ CODE ("\x84\xDB") // test bl, bl
+ CODE ("\x0F\x84\x00\x00\x00\x00") // jz "offsets[arg]"
+ break;
+ case END:
+ // We know that the cell is zero, make this an "if", not a "loop";
+ // this doesn't have much of an effect in practice
+ if (!arg)
+ break;
+
+ if (!i || !sets_flags[i - 1])
+ CODE ("\x84\xDB") // test bl, bl
+ CODE ("\x0F\x85\x00\x00\x00\x00") // jnz "offsets[arg]"
+ break;
+ }
+
+ // No sense in reading it out when we overwrite it immediately;
+ // this doesn't have much of an effect in practice
+ if (irb[i].cmd == LEFT || irb[i].cmd == RIGHT)
+ if (i + 1 >= irb_len
+ || irb[i + 1].cmd != SET
+ || irb[i + 1].offset != 0)
+ CODE ("\x8A\x18") // mov bl, [rax]
+ }
+ // When there is a loop at the end we need to be able to jump past it
+ offsets[irb_len] = buffer.len;
+
+ // Write an epilog which handles all the OS interfacing
+ //
+ // System V x86-64 ABI:
+ // rax <-> both syscall number and return value
+ // args -> rdi, rsi, rdx, r10, r8, r9
+ // trashed <- rcx, r11
+
+ enum { SYS_READ = 0, SYS_WRITE = 1, SYS_EXIT = 60 };
+
+ CODE ("\xB8") DD (SYS_EXIT) // mov eax, 0x3c
+ CODE ("\x48\x31\xFF") // xor rdi, rdi
+ CODE ("\x0F\x05") // syscall
+
+ size_t fatal_offset = buffer.len;
+ CODE ("\x48\x89\xF7") // mov rdi, rsi -- use the string in rsi
+ CODE ("\x30\xC0") // xor al, al -- look for the nil byte
+ CODE ("\x48\x31\xC9") // xor rcx, rcx
+ CODE ("\x48\xF7\xD1") // not rcx -- start from -1
+ CODE ("\xFC" "\xF2\xAE") // cld; repne scasb -- decrement until found
+ CODE ("\x48\xF7\xD1") // not rcx
+ CODE ("\x48\x8D\x51\xFF") // lea rdx, [rcx-1] -- save length in rdx
+ CODE ("\xB8") DD (SYS_WRITE) // mov eax, "SYS_WRITE"
+ CODE ("\xBF") DD (2) // mov edi, "STDERR_FILENO"
+ CODE ("\x0F\x05") // syscall
+
+ CODE ("\xB8") DD (SYS_EXIT) // mov eax, "SYS_EXIT"
+ CODE ("\xBF") DD (1) // mov edi, "EXIT_FAILURE"
+ CODE ("\x0F\x05") // syscall
+
+ size_t read_offset = buffer.len;
+ CODE ("\x50") // push rax -- save tape position
+ CODE ("\xB8") DD (SYS_READ) // mov eax, "SYS_READ"
+ CODE ("\x48\x89\xC7") // mov rdi, rax -- STDIN_FILENO
+ CODE ("\x66\x6A\x00") // push word 0 -- the default value for EOF
+ CODE ("\x48\x89\xE6") // mov rsi, rsp -- the char starts at rsp
+ CODE ("\xBA") DD (1) // mov edx, 1 -- count
+ CODE ("\x0F\x05") // syscall
+ CODE ("\x66\x5B") // pop bx
+
+ CODE ("\x48\x83\xF8\x00") // cmp rax, 0
+ CODE ("\x48\x8D\x35") DD (4) // lea rsi, [rel read_message]
+ CODE ("\x7C") // jl "fatal_offset" -- write failure message
+ DB ((intptr_t) fatal_offset - (intptr_t) (buffer.len + 1))
+ CODE ("\x58") // pop rax -- restore tape position
+ CODE ("\xC3") // ret
+ CODE ("fatal: read failed\n\0")
+
+ size_t write_offset = buffer.len;
+ CODE ("\x50") // push rax -- save tape position
+ CODE ("\xB8") DD (SYS_WRITE) // mov eax, "SYS_WRITE"
+ CODE ("\x48\x89\xC7") // mov rdi, rax -- STDOUT_FILENO
+ CODE ("\x66\x53") // push bx
+ CODE ("\x48\x89\xE6") // mov rsi, rsp -- the char starts at rsp
+ CODE ("\xBA") DD (1) // mov edx, 1 -- count
+ CODE ("\x0F\x05") // syscall
+ CODE ("\x66\x5B") // pop bx
+
+ CODE ("\x48\x83\xF8\x00") // cmp rax, 0
+ CODE ("\x48\x8D\x35") DD (4) // lea rsi, [rel write_message]
+ CODE ("\x7C") // jl "fatal_offset" -- write failure message
+ DB ((intptr_t) fatal_offset - (intptr_t) (buffer.len + 1))
+ CODE ("\x58") // pop rax -- restore tape position
+ CODE ("\xC3") // ret
+ CODE ("fatal: write failed\n\0")
+
+ // Now that we know where each instruction is, fill in relative jumps
+ for (size_t i = 0; i < irb_len; i++)
+ {
+ if (!irb[i].arg)
+ continue;
+
+ // This must accurately reflect the code generators
+ intptr_t target, fixup = offsets[i];
+ if (irb[i].cmd == BEGIN || irb[i].cmd == END)
+ {
+ fixup += (i && sets_flags[i - 1]) ? 2 : 4;
+ target = offsets[irb[i].arg];
+ }
+ else if (irb[i].cmd == IN) { fixup++; target = read_offset; }
+ else if (irb[i].cmd == OUT) { fixup++; target = write_offset; }
+ else continue;
+
+ uint64_t v = target - (fixup + 4);
+ memcpy (buffer.str + fixup, LE (v), 4);
+ }
+ free (offsets);
+ free (sets_flags);
+
+// - - Output - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+ // Now that we know how long the machine code is, we can write the header.
+ // Note that for PIE we would need to depend on the dynamic linker, so no.
+ //
+ // Recommended reading:
+ // http://www.muppetlabs.com/~breadbox/software/tiny/teensy.html
+ // man 5 elf
+
+ struct str code = buffer;
+ str_init (&buffer);
+
+ enum
+ {
+ ELF_HEADER_SIZE = 64, // size of the ELF header
+ ELF_PROGRAM_ENTRY_SIZE = 56, // size of a program header
+ ELF_META_SIZE = ELF_HEADER_SIZE + 2 * ELF_PROGRAM_ENTRY_SIZE
+ };
+
+ // ELF header
+ CODE ("\x7F" "ELF\x02\x01\x01") // ELF, 64-bit, little endian, v1
+ CODE ("\x00\x00" "\0\0\0\0\0\0\0") // Unix System V ABI, v0, padding
+ DW (2) DW (62) DD (1) // executable, x86-64, v1
+ DQ (ELF_LOAD_CODE + ELF_META_SIZE) // entry point address
+ DQ (ELF_HEADER_SIZE) DQ (0) // program, section header offset
+ DD (0) // no processor-specific flags
+ DW (ELF_HEADER_SIZE) // ELF header size
+ DW (ELF_PROGRAM_ENTRY_SIZE) DW (2) // program hdr tbl entry size, count
+ DW (0) DW (0) // section hdr tbl entry size, count
+ DW (0) // no section index for strings
+
+ // Program header for code
+ // The entry point address seems to require alignment, so map start of file
+ DD (1) DD (5) // PT_LOAD, PF_R | PF_X
+ DQ (0) // offset within the file
+ DQ (ELF_LOAD_CODE) // address in virtual memory
+ DQ (ELF_LOAD_CODE) // address in physical memory
+ DQ (code.len + ELF_META_SIZE) // length within the file
+ DQ (code.len + ELF_META_SIZE) // length within memory
+ DQ (4096) // segment alignment
+
+ // Program header for the tape
+ DD (1) DD (6) // PT_LOAD, PF_R | PF_W
+ DQ (0) // offset within the file
+ DQ (ELF_LOAD_DATA) // address in virtual memory
+ DQ (ELF_LOAD_DATA) // address in physical memory
+ DQ (0) // length within the file
+ DQ (1 << 20) // one megabyte of memory
+ DQ (4096) // segment alignment
+
+ // The section header table is optional and we don't need it for anything
+
+ FILE *output_file;
+ if (!(output_file = fopen (output_path, "w")))
+ exit_fatal ("fopen: %s: %s\n", output_path, strerror (errno));
+
+ fwrite (buffer.str, buffer.len, 1, output_file);
+ fwrite (code.str, code.len, 1, output_file);
+ fclose (output_file);
+ return 0;
+}
diff --git a/interpreters/Makefile b/interpreters/Makefile
new file mode 100644
index 0000000..3e73cf5
--- /dev/null
+++ b/interpreters/Makefile
@@ -0,0 +1,14 @@
+CC = c99
+CFLAGS = -O3
+
+NAMES = bf bf-faster-loops bf-optimizing \
+ bf-jit bf-jit-opt bf-jit-unsafe bf-jit-unsafe-opt
+
+all: $(NAMES)
+
+%: %.c
+ $(CC) $(CPPFLAGS) $(CFLAGS) $< -o $@
+clean:
+ rm -f $(NAMES)
+
+.PHONY: all clean
diff --git a/interpreters/README.adoc b/interpreters/README.adoc
new file mode 100644
index 0000000..ecde608
--- /dev/null
+++ b/interpreters/README.adoc
@@ -0,0 +1,15 @@
+This directory contains several Brainfuck interpreters in various states of
+sophistication, from the simplest approach to an optimizing JIT compiler:
+
+ * `bf.c` is the stupidest one and the oldest by far
+ * `bf-faster-loops.c` precomputes loop jumps
+ * `bf-optimizing.c` improves on that by changing `[-]+` loops into assignments
+ * `bf-jit.c` adds JIT compilation for Intel x86-64
+ * `bf-jit-opt.c` tries a bit harder to avoid looping on the current value
+ * `bf-jit-unsafe.c` abolishes all boundary checks when moving across the tape
+ * `bf-jit-unsafe-opt.c` makes use of immediate offsets to modify values
+
+I recommend using a tool such as 'meld' to view the differences.
+
+Just run `make` in this directory to have them all built, and append
+`CPPFLAGS=-DDEBUG` to get dumps of the IR for the more sophisticated JITs.
diff --git a/interpreters/bf-faster-loops.c b/interpreters/bf-faster-loops.c
new file mode 100644
index 0000000..e301d95
--- /dev/null
+++ b/interpreters/bf-faster-loops.c
@@ -0,0 +1,151 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h>
+#include <assert.h>
+#include <errno.h>
+
+#define exit_fatal(...) \
+ do { \
+ fprintf (stderr, "fatal: " __VA_ARGS__); \
+ exit (EXIT_FAILURE); \
+ } while (0)
+
+// --- Safe memory management --------------------------------------------------
+
+static void *
+xmalloc (size_t n)
+{
+ void *p = malloc (n);
+ if (!p)
+ exit_fatal ("malloc: %s\n", strerror (errno));
+ return p;
+}
+
+static void *
+xrealloc (void *o, size_t n)
+{
+ void *p = realloc (o, n);
+ if (!p && n)
+ exit_fatal ("realloc: %s\n", strerror (errno));
+ return p;
+}
+
+// --- Dynamically allocated strings -------------------------------------------
+
+struct str
+{
+ char *str; ///< String data, null terminated
+ size_t alloc; ///< How many bytes are allocated
+ size_t len; ///< How long the string actually is
+};
+
+static void
+str_init (struct str *self)
+{
+ self->alloc = 16;
+ self->len = 0;
+ self->str = strcpy (xmalloc (self->alloc), "");
+}
+
+static void
+str_ensure_space (struct str *self, size_t n)
+{
+ // We allocate at least one more byte for the terminating null character
+ size_t new_alloc = self->alloc;
+ while (new_alloc <= self->len + n)
+ new_alloc <<= 1;
+ if (new_alloc != self->alloc)
+ self->str = xrealloc (self->str, (self->alloc = new_alloc));
+}
+
+static void
+str_append_data (struct str *self, const void *data, size_t n)
+{
+ str_ensure_space (self, n);
+ memcpy (self->str + self->len, data, n);
+ self->str[self->len += n] = '\0';
+}
+
+static void
+str_append_c (struct str *self, char c)
+{
+ str_append_data (self, &c, 1);
+}
+
+// --- Main --------------------------------------------------------------------
+
+int
+main (int argc, char *argv[])
+{
+ struct str program; str_init (&program);
+ struct str data; str_init (&data);
+
+ int c;
+ while ((c = fgetc (stdin)) != EOF)
+ str_append_c (&program, c);
+ if (ferror (stdin))
+ exit_fatal ("can't read program\n");
+
+ FILE *input = fopen ("/dev/tty", "rb");
+ if (!input)
+ exit_fatal ("can't open terminal for reading\n");
+
+ size_t *pairs = xmalloc (sizeof *pairs * program.len);
+ size_t *stack = xmalloc (sizeof *stack * program.len);
+
+ size_t nesting = 0;
+ for (size_t i = 0; i < program.len; i++)
+ {
+ switch (program.str[i])
+ {
+ case '[':
+ stack[nesting++] = i;
+ break;
+ case ']':
+ assert (nesting > 0);
+
+ --nesting;
+ pairs[stack[nesting]] = i;
+ pairs[i] = stack[nesting];
+ }
+ }
+ assert (nesting == 0);
+
+ size_t dataptr = 0;
+ str_append_c (&data, 0);
+
+ for (size_t i = 0; i < program.len; i++)
+ {
+ switch (program.str[i])
+ {
+ case '>':
+ assert (dataptr != SIZE_MAX);
+ if (++dataptr == data.len)
+ str_append_c (&data, 0);
+ break;
+ case '<':
+ assert (dataptr != 0);
+ dataptr--;
+ break;
+
+ case '+': data.str[dataptr]++; break;
+ case '-': data.str[dataptr]--; break;
+
+ case '.':
+ fputc (data.str[dataptr], stdout);
+ break;
+ case ',':
+ data.str[dataptr] = c = fgetc (input);
+ assert (c != EOF);
+ break;
+
+ case '[': if (!data.str[dataptr]) i = pairs[i]; break;
+ case ']': if ( data.str[dataptr]) i = pairs[i]; break;
+
+ default:
+ break;
+ }
+ }
+ return 0;
+}
diff --git a/interpreters/bf-jit-opt.c b/interpreters/bf-jit-opt.c
new file mode 100644
index 0000000..3b24ad3
--- /dev/null
+++ b/interpreters/bf-jit-opt.c
@@ -0,0 +1,495 @@
+// This is an exercise in futility more than anything else
+#define _GNU_SOURCE
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <assert.h>
+#include <errno.h>
+
+#if (defined __x86_64__ || defined __amd64__) && defined __unix__
+ #include <sys/mman.h>
+#else
+ #error Platform not supported
+#endif
+
+#define exit_fatal(...) \
+ do { \
+ fprintf (stderr, "fatal: " __VA_ARGS__); \
+ exit (EXIT_FAILURE); \
+ } while (0)
+
+// --- Safe memory management --------------------------------------------------
+
+static void *
+xcalloc (size_t m, size_t n)
+{
+ void *p = calloc (m, n);
+ if (!p)
+ exit_fatal ("calloc: %s\n", strerror (errno));
+ return p;
+}
+
+static void *
+xrealloc (void *o, size_t n)
+{
+ void *p = realloc (o, n);
+ if (!p && n)
+ exit_fatal ("realloc: %s\n", strerror (errno));
+ return p;
+}
+
+// --- Dynamically allocated strings -------------------------------------------
+
+struct str
+{
+ char *str; ///< String data, null terminated
+ size_t alloc; ///< How many bytes are allocated
+ size_t len; ///< How long the string actually is
+};
+
+static void
+str_init (struct str *self)
+{
+ self->len = 0;
+ self->str = xcalloc (1, (self->alloc = 16));
+}
+
+static void
+str_ensure_space (struct str *self, size_t n)
+{
+ // We allocate at least one more byte for the terminating null character
+ size_t new_alloc = self->alloc;
+ while (new_alloc <= self->len + n)
+ new_alloc <<= 1;
+ if (new_alloc != self->alloc)
+ self->str = xrealloc (self->str, (self->alloc = new_alloc));
+}
+
+static void
+str_append_data (struct str *self, const void *data, size_t n)
+{
+ str_ensure_space (self, n);
+ memcpy (self->str + self->len, data, n);
+ self->str[self->len += n] = '\0';
+}
+
+static void
+str_append_c (struct str *self, char c)
+{
+ str_append_data (self, &c, 1);
+}
+
+// --- Application -------------------------------------------------------------
+
+struct str data; ///< Data tape
+volatile size_t dataptr; ///< Current location on the tape
+FILE *input; ///< User input
+
+enum command { RIGHT, LEFT, INC, DEC, SET, IN, OUT, BEGIN, END,
+ EAT, INCACC, DECACC };
+bool grouped[] = { 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0 };
+struct instruction { enum command cmd; size_t arg; };
+#define INSTRUCTION(c, a) (struct instruction) { (c), (a) }
+
+// - - Callbacks - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+// Some things I just really don't want to write in assembly even though it
+// is effectively a big performance hit, eliminating the advantage of JIT
+
+static void
+right (size_t arg)
+{
+ assert (SIZE_MAX - dataptr > arg);
+ dataptr += arg;
+
+ while (dataptr >= data.len)
+ str_append_c (&data, 0);
+}
+
+static void
+left (size_t arg)
+{
+ assert (dataptr >= arg);
+ dataptr -= arg;
+}
+
+static void
+cin (void)
+{
+ int c;
+ data.str[dataptr] = c = fgetc (input);
+ assert (c != EOF);
+}
+
+// - - Main - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+#ifdef DEBUG
+static void
+debug_dump (const char *filename, struct instruction *in, size_t len)
+{
+ FILE *fp = fopen (filename, "w");
+ long indent = 0;
+ for (size_t i = 0; i < len; i++)
+ {
+ if (in[i].cmd == END)
+ indent--;
+ for (long k = 0; k < indent; k++)
+ fprintf (fp, " ");
+
+ switch (in[i].cmd)
+ {
+ case RIGHT: fprintf (fp, "RIGHT %zu\n", in[i].arg); break;
+ case LEFT: fprintf (fp, "LEFT %zu\n", in[i].arg); break;
+ case INC: fprintf (fp, "INC %zu\n", in[i].arg); break;
+ case DEC: fprintf (fp, "DEC %zu\n", in[i].arg); break;
+ case OUT: fprintf (fp, "OUT %zu\n", in[i].arg); break;
+ case IN: fprintf (fp, "IN %zu\n", in[i].arg); break;
+ case BEGIN: fprintf (fp, "BEGIN %zu\n", in[i].arg); break;
+ case END: fprintf (fp, "END %zu\n", in[i].arg); break;
+ case SET: fprintf (fp, "SET %zu\n", in[i].arg); break;
+ case EAT: fprintf (fp, "EAT %zu\n", in[i].arg); break;
+ case INCACC: fprintf (fp, "INCACC %zu\n", in[i].arg); break;
+ case DECACC: fprintf (fp, "DECACC %zu\n", in[i].arg); break;
+ }
+ if (in[i].cmd == BEGIN)
+ indent++;
+ }
+ fclose (fp);
+}
+#else
+#define debug_dump(...)
+#endif
+
+int
+main (int argc, char *argv[])
+{
+ (void) argc;
+ (void) argv;
+
+ struct str program;
+ str_init (&program);
+
+ int c;
+ while ((c = fgetc (stdin)) != EOF)
+ str_append_c (&program, c);
+ if (ferror (stdin))
+ exit_fatal ("can't read program\n");
+ if (!(input = fopen ("/dev/tty", "rb")))
+ exit_fatal ("can't open terminal for reading\n");
+
+// - - Decode and group - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+ struct instruction *parsed = xcalloc (sizeof *parsed, program.len);
+ size_t parsed_len = 0;
+
+ for (size_t i = 0; i < program.len; i++)
+ {
+ enum command cmd;
+ switch (program.str[i])
+ {
+ case '>': cmd = RIGHT; break;
+ case '<': cmd = LEFT; break;
+ case '+': cmd = INC; break;
+ case '-': cmd = DEC; break;
+ case '.': cmd = OUT; break;
+ case ',': cmd = IN; break;
+ case '[': cmd = BEGIN; break;
+ case ']': cmd = END; break;
+ default: continue;
+ }
+
+ // The most basic optimization is to group identical commands together
+ if (!parsed_len || !grouped[cmd] || parsed[parsed_len - 1].cmd != cmd)
+ parsed_len++;
+
+ parsed[parsed_len - 1].cmd = cmd;
+ parsed[parsed_len - 1].arg++;
+ }
+
+// - - Optimization passes - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+ debug_dump ("bf-no-opt.txt", parsed, parsed_len);
+
+ size_t in = 0, out = 0;
+ for (; in < parsed_len; in++, out++)
+ {
+ // This shows up in mandelbrot.bf a lot but actually helps hanoi.bf
+ if (in + 5 < parsed_len
+ && parsed[in].cmd == BEGIN && parsed[in + 5].cmd == END
+ && parsed[in + 1].cmd == DEC && parsed[in + 1].arg == 1
+
+ && parsed[in + 2].cmd == LEFT && parsed[in + 4].cmd == RIGHT
+ && parsed[in + 2].arg == parsed[in + 4].arg
+
+ && (parsed[in + 3].cmd == INC || parsed[in + 3].cmd == DEC)
+ && parsed[in + 3].arg == 1)
+ {
+ // This mustn't make the move when the cell is zero already
+ parsed[out] = parsed[in];
+ parsed[out + 1] = INSTRUCTION (EAT, 0);
+ parsed[out + 2] = parsed[in + 2];
+ parsed[out + 3] = INSTRUCTION
+ (parsed[in + 3].cmd == INC ? INCACC : DECACC, 0);
+ parsed[out + 4] = parsed[in + 4];
+ // This disables the looping further in the code;
+ // this doesn't have much of an effect in practice
+ parsed[out + 5] = INSTRUCTION (END, 0);
+ in += 5;
+ out += 5;
+ }
+ // The simpler case that cannot crash and thus can avoid the loop
+ else if (in + 5 < parsed_len
+ && parsed[in].cmd == BEGIN && parsed[in + 5].cmd == END
+ && parsed[in + 1].cmd == DEC && parsed[in + 1].arg == 1
+
+ && parsed[in + 2].cmd == RIGHT && parsed[in + 4].cmd == LEFT
+ && parsed[in + 2].arg == parsed[in + 4].arg
+
+ && (parsed[in + 3].cmd == INC || parsed[in + 3].cmd == DEC)
+ && parsed[in + 3].arg == 1)
+ {
+ parsed[out] = INSTRUCTION (EAT, 0);
+ parsed[out + 1] = parsed[in + 2];
+ parsed[out + 2] = INSTRUCTION
+ (parsed[in + 3].cmd == INC ? INCACC : DECACC, 0);
+ parsed[out + 3] = parsed[in + 4];
+ in += 5;
+ out += 3;
+ }
+ else if (in + 2 < parsed_len
+ && parsed[in ].cmd == BEGIN
+ && parsed[in + 1].cmd == DEC && parsed[in + 1].arg == 1
+ && parsed[in + 2].cmd == END)
+ {
+ parsed[out] = INSTRUCTION (SET, 0);
+ in += 2;
+ }
+ else if (out && parsed[out - 1].cmd == SET && parsed[in].cmd == INC)
+ parsed[--out].arg += parsed[in].arg;
+ else if (out != in)
+ parsed[out] = parsed[in];
+ }
+ parsed_len = out;
+
+ for (in = 0, out = 0; in < parsed_len; in++, out++)
+ {
+ ssize_t dir = 0;
+ if (parsed[in].cmd == RIGHT)
+ dir = parsed[in].arg;
+ else if (parsed[in].cmd == LEFT)
+ dir = -(ssize_t) parsed[in].arg;
+ else
+ {
+ parsed[out] = parsed[in];
+ continue;
+ }
+
+ for (; in + 1 < parsed_len; in++)
+ {
+ if (parsed[in + 1].cmd == RIGHT)
+ dir += parsed[in + 1].arg;
+ else if (parsed[in + 1].cmd == LEFT)
+ dir -= (ssize_t) parsed[in + 1].arg;
+ else
+ break;
+ }
+
+ if (!dir)
+ out--;
+ else if (dir > 0)
+ parsed[out] = INSTRUCTION (RIGHT, dir);
+ else
+ parsed[out] = INSTRUCTION (LEFT, -dir);
+ }
+ parsed_len = out;
+
+ debug_dump ("bf-optimized.txt", parsed, parsed_len);
+
+// - - Loop pairing - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+ size_t nesting = 0;
+ size_t *stack = xcalloc (sizeof *stack, parsed_len);
+ for (size_t i = 0; i < parsed_len; i++)
+ {
+ switch (parsed[i].cmd)
+ {
+ case BEGIN:
+ stack[nesting++] = i;
+ break;
+ case END:
+ assert (nesting > 0);
+
+ --nesting;
+ parsed[stack[nesting]].arg = i + 1;
+
+ // Looping can be disabled by optimizations
+ if (parsed[i].arg)
+ parsed[i].arg = stack[nesting] + 1;
+ default:
+ break;
+ }
+ }
+ free (stack);
+ assert (nesting == 0);
+
+ debug_dump ("bf-final.txt", parsed, parsed_len);
+
+// - - JIT - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+ // Functions preserve the registers rbx, rsp, rbp, r12, r13, r14, and r15;
+ // while rax, rdi, rsi, rdx, rcx, r8, r9, r10, r11 are scratch registers.
+
+ str_init (&program);
+ size_t *offsets = xcalloc (sizeof *offsets, parsed_len + 1);
+ uint8_t *arith = xcalloc (sizeof *arith, parsed_len);
+
+#define CODE(x) { char t[] = x; str_append_data (&program, t, sizeof t - 1); }
+#define WORD(x) { size_t t = (size_t)(x); str_append_data (&program, &t, 8); }
+#define DWRD(x) { size_t t = (size_t)(x); str_append_data (&program, &t, 4); }
+
+ CODE ("\x49\xBD") WORD (&dataptr) // mov r13, qword "&dataptr"
+ CODE ("\x49\xBF") WORD (&data.str) // mov r15, qword "&data.str"
+ CODE ("\x4D\x8B\x37") // mov r14, qword [r15]
+ CODE ("\x30\xDB") // xor bl, bl
+
+ for (size_t i = 0; i < parsed_len; i++)
+ {
+ offsets[i] = program.len;
+
+ size_t arg = parsed[i].arg;
+ assert (arg <= UINT32_MAX);
+ switch (parsed[i].cmd)
+ {
+ case RIGHT:
+ CODE ("\x41\x88\x1E") // mov [r14], bl
+ CODE ("\xBF") DWRD (arg) // mov edi, "arg"
+ CODE ("\x48\xB8") WORD (right) // mov rax, "right"
+ CODE ("\xFF\xD0") // call rax
+
+ // The data could get reallocated, so reload the address
+ CODE ("\x4D\x8B\x37") // mov r14, qword [r15]
+ CODE ("\x4D\x03\x75\x00") // add r14, [r13]
+ break;
+ case LEFT:
+ CODE ("\x41\x88\x1E") // mov [r14], bl
+ CODE ("\xBF") DWRD (arg) // mov edi, "arg"
+ CODE ("\x49\x29\xFE") // sub r14, rdi -- optimistic
+ CODE ("\x48\xB8") WORD (left) // mov rax, "left"
+ CODE ("\xFF\xD0") // call rax
+ break;
+
+ case EAT:
+ CODE ("\x41\x88\xDC") // mov r12b, bl
+ CODE ("\x30\xDB") // xor bl, bl
+ arith[i] = 1;
+ break;
+ case INCACC:
+ CODE ("\x44\x00\xE3") // add bl, r12b
+ arith[i] = 1;
+ break;
+ case DECACC:
+ CODE ("\x44\x28\xE3") // sub bl, r12b
+ arith[i] = 1;
+ break;
+
+ case INC:
+ CODE ("\x80\xC3") // add bl, "arg"
+ str_append_c (&program, arg);
+ arith[i] = 1;
+ break;
+ case DEC:
+ CODE ("\x80\xEB") // sub bl, "arg"
+ str_append_c (&program, arg);
+ arith[i] = 1;
+ break;
+ case SET:
+ CODE ("\xB3") // mov bl, "arg"
+ str_append_c (&program, arg);
+ break;
+
+ case OUT:
+ CODE ("\x48\x0F\xB6\xFB") // movzx rdi, bl
+ CODE ("\x48\xBE") WORD (stdout) // mov rsi, "stdout"
+ CODE ("\x48\xB8") WORD (fputc) // mov rax, "fputc"
+ CODE ("\xFF\xD0") // call rax
+ break;
+ case IN:
+ CODE ("\x48\xB8") WORD (cin) // mov rax, "cin"
+ CODE ("\xFF\xD0") // call rax
+ CODE ("\x41\x8A\x1E") // mov bl, [r14]
+ break;
+
+ case BEGIN:
+ // Don't test the register when the flag has been set already;
+ // this doesn't have much of an effect in practice
+ if (!i || !arith[i - 1])
+ CODE ("\x84\xDB") // test bl, bl
+ CODE ("\x0F\x84\x00\x00\x00\x00") // jz "offsets[i]"
+ break;
+ case END:
+ // We know that the cell is zero, make this an "if", not a "loop";
+ // this doesn't have much of an effect in practice
+ if (!arg)
+ break;
+
+ if (!i || !arith[i - 1])
+ CODE ("\x84\xDB") // test bl, bl
+ CODE ("\x0F\x85\x00\x00\x00\x00") // jnz "offsets[i]"
+ break;
+ }
+
+ // No sense in reading it out when we overwrite it immediately;
+ // this doesn't have much of an effect in practice
+ if (parsed[i].cmd == LEFT || parsed[i].cmd == RIGHT)
+ if (i + 1 >= parsed_len
+ || parsed[i + 1].cmd != SET)
+ CODE ("\x41\x8A\x1E") // mov bl, [r14]
+ }
+ // When there is a loop at the end we need to be able to jump past it
+ offsets[parsed_len] = program.len;
+ str_append_c (&program, '\xC3'); // ret
+
+ // Now that we know where each instruction is, fill in relative jumps;
+ // this must accurately reflect code generators for BEGIN and END
+ for (size_t i = 0; i < parsed_len; i++)
+ {
+ if ((parsed[i].cmd != BEGIN && parsed[i].cmd != END)
+ || !parsed[i].arg)
+ continue;
+
+ size_t fixup = offsets[i] + 2;
+ if (!i || !arith[i - 1])
+ fixup += 2;
+
+ *(int32_t *)(program.str + fixup) =
+ ((intptr_t)(offsets[parsed[i].arg]) - (intptr_t)(fixup + 4));
+ }
+ free (offsets);
+ free (arith);
+
+#ifdef DEBUG
+ FILE *bin = fopen ("bf-jit.bin", "w");
+ fwrite (program.str, program.len, 1, bin);
+ fclose (bin);
+#endif
+
+// - - Runtime - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+ // Some systems may have W^X
+ void *executable = mmap (NULL, program.len, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ if (!executable)
+ exit_fatal ("mmap: %s\n", strerror (errno));
+
+ memcpy (executable, program.str, program.len);
+ if (mprotect (executable, program.len, PROT_READ | PROT_EXEC))
+ exit_fatal ("mprotect: %s\n", strerror (errno));
+
+ str_init (&data);
+ str_append_c (&data, 0);
+ ((void (*) (void)) executable)();
+ return 0;
+}
diff --git a/interpreters/bf-jit-unsafe-opt.c b/interpreters/bf-jit-unsafe-opt.c
new file mode 100644
index 0000000..88a7980
--- /dev/null
+++ b/interpreters/bf-jit-unsafe-opt.c
@@ -0,0 +1,617 @@
+// This is an exercise in futility more than anything else
+#define _GNU_SOURCE
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <assert.h>
+#include <errno.h>
+
+#if (defined __x86_64__ || defined __amd64__) && defined __unix__
+ #include <unistd.h>
+ #include <sys/mman.h>
+#else
+ #error Platform not supported
+#endif
+
+#define exit_fatal(...) \
+ do { \
+ fprintf (stderr, "fatal: " __VA_ARGS__); \
+ exit (EXIT_FAILURE); \
+ } while (0)
+
+// --- Safe memory management --------------------------------------------------
+
+static void *
+xcalloc (size_t m, size_t n)
+{
+ void *p = calloc (m, n);
+ if (!p)
+ exit_fatal ("calloc: %s\n", strerror (errno));
+ return p;
+}
+
+static void *
+xrealloc (void *o, size_t n)
+{
+ void *p = realloc (o, n);
+ if (!p && n)
+ exit_fatal ("realloc: %s\n", strerror (errno));
+ return p;
+}
+
+// --- Dynamically allocated strings -------------------------------------------
+
+struct str
+{
+ char *str; ///< String data, null terminated
+ size_t alloc; ///< How many bytes are allocated
+ size_t len; ///< How long the string actually is
+};
+
+static void
+str_init (struct str *self)
+{
+ self->len = 0;
+ self->str = xcalloc (1, (self->alloc = 16));
+}
+
+static void
+str_ensure_space (struct str *self, size_t n)
+{
+ // We allocate at least one more byte for the terminating null character
+ size_t new_alloc = self->alloc;
+ while (new_alloc <= self->len + n)
+ new_alloc <<= 1;
+ if (new_alloc != self->alloc)
+ self->str = xrealloc (self->str, (self->alloc = new_alloc));
+}
+
+static void
+str_append_data (struct str *self, const void *data, size_t n)
+{
+ str_ensure_space (self, n);
+ memcpy (self->str + self->len, data, n);
+ self->str[self->len += n] = '\0';
+}
+
+static void
+str_append_c (struct str *self, char c)
+{
+ str_append_data (self, &c, 1);
+}
+
+// --- Application -------------------------------------------------------------
+
+enum command { RIGHT, LEFT, INC, DEC, SET, IN, OUT, BEGIN, END,
+ EAT, INCACC, DECACC };
+bool grouped[] = { 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0 };
+struct instruction { enum command cmd; int offset; size_t arg; };
+#define INSTRUCTION(c, o, a) (struct instruction) { (c), (o), (a) }
+
+// - - Callbacks - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+FILE *input; ///< User input
+
+static int
+cin (void)
+{
+ int c = fgetc (input);
+ assert (c != EOF);
+ return c;
+}
+
+// - - Main - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+#ifdef DEBUG
+static void
+debug_dump (const char *filename, struct instruction *in, size_t len)
+{
+ FILE *fp = fopen (filename, "w");
+ long indent = 0;
+ for (size_t i = 0; i < len; i++)
+ {
+ if (in[i].cmd == END)
+ indent--;
+ for (long k = 0; k < indent; k++)
+ fprintf (fp, " ");
+
+ switch (in[i].cmd)
+ {
+ case RIGHT: fputs ("RIGHT ", fp); break;
+ case LEFT: fputs ("LEFT ", fp); break;
+ case INC: fputs ("INC ", fp); break;
+ case DEC: fputs ("DEC ", fp); break;
+ case OUT: fputs ("OUT ", fp); break;
+ case IN: fputs ("IN ", fp); break;
+ case BEGIN: fputs ("BEGIN ", fp); break;
+ case END: fputs ("END ", fp); break;
+ case SET: fputs ("SET ", fp); break;
+ case EAT: fputs ("EAT ", fp); break;
+ case INCACC: fputs ("INCACC", fp); break;
+ case DECACC: fputs ("DECACC", fp); break;
+ }
+ fprintf (fp, " %zu [%d]\n", in[i].arg, in[i].offset);
+ if (in[i].cmd == BEGIN)
+ indent++;
+ }
+ fclose (fp);
+}
+#else
+#define debug_dump(...)
+#endif
+
+int
+main (int argc, char *argv[])
+{
+ (void) argc;
+ (void) argv;
+
+ struct str program;
+ str_init (&program);
+
+ int c;
+ while ((c = fgetc (stdin)) != EOF)
+ str_append_c (&program, c);
+ if (ferror (stdin))
+ exit_fatal ("can't read program\n");
+ if (!(input = fopen ("/dev/tty", "rb")))
+ exit_fatal ("can't open terminal for reading\n");
+
+// - - Decode and group - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+ struct instruction *parsed = xcalloc (sizeof *parsed, program.len);
+ size_t parsed_len = 0;
+
+ for (size_t i = 0; i < program.len; i++)
+ {
+ enum command cmd;
+ switch (program.str[i])
+ {
+ case '>': cmd = RIGHT; break;
+ case '<': cmd = LEFT; break;
+ case '+': cmd = INC; break;
+ case '-': cmd = DEC; break;
+ case '.': cmd = OUT; break;
+ case ',': cmd = IN; break;
+ case '[': cmd = BEGIN; break;
+ case ']': cmd = END; break;
+ default: continue;
+ }
+
+ // The most basic optimization is to group identical commands together
+ if (!parsed_len || !grouped[cmd] || parsed[parsed_len - 1].cmd != cmd)
+ parsed_len++;
+
+ parsed[parsed_len - 1].cmd = cmd;
+ parsed[parsed_len - 1].arg++;
+ }
+
+// - - Optimization passes - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+ debug_dump ("bf-no-opt.txt", parsed, parsed_len);
+
+ size_t in = 0, out = 0;
+ for (; in < parsed_len; in++, out++)
+ {
+ if (in + 2 < parsed_len
+ && parsed[in ].cmd == BEGIN
+ && parsed[in + 1].cmd == DEC && parsed[in + 1].arg == 1
+ && parsed[in + 2].cmd == END)
+ {
+ parsed[out] = INSTRUCTION (SET, 0, 0);
+ in += 2;
+ }
+ else if (out && parsed[out - 1].cmd == SET && parsed[in].cmd == INC)
+ parsed[--out].arg += parsed[in].arg;
+ else if (out != in)
+ parsed[out] = parsed[in];
+ }
+ parsed_len = out;
+
+ debug_dump ("bf-pre-offsets.txt", parsed, parsed_len);
+
+ // Add offsets to INC/DEC/SET stuck between LEFT/RIGHT
+ // and compress the LEFT/RIGHT sequences
+ for (in = 0, out = 0; in < parsed_len; in++, out++)
+ {
+ ssize_t dir = 0;
+ if (parsed[in].cmd == RIGHT)
+ dir = parsed[in].arg;
+ else if (parsed[in].cmd == LEFT)
+ dir = -(ssize_t) parsed[in].arg;
+ else
+ {
+ parsed[out] = parsed[in];
+ continue;
+ }
+
+ while (in + 2 < parsed_len)
+ {
+ // An immediate offset has its limits
+ if (dir < INT8_MIN || dir > INT8_MAX)
+ break;
+
+ ssize_t diff;
+ if (parsed[in + 2].cmd == RIGHT)
+ diff = parsed[in + 2].arg;
+ else if (parsed[in + 2].cmd == LEFT)
+ diff = -(ssize_t) parsed[in + 2].arg;
+ else
+ break;
+
+ int cmd = parsed[in + 1].cmd;
+ if (cmd != INC && cmd != DEC && cmd != SET)
+ break;
+
+ parsed[out] = parsed[in + 1];
+ parsed[out].offset = dir;
+
+ dir += diff;
+ out += 1;
+ in += 2;
+ }
+
+ for (; in + 1 < parsed_len; in++)
+ {
+ if (parsed[in + 1].cmd == RIGHT)
+ dir += parsed[in + 1].arg;
+ else if (parsed[in + 1].cmd == LEFT)
+ dir -= (ssize_t) parsed[in + 1].arg;
+ else
+ break;
+ }
+
+ if (!dir)
+ out--;
+ else if (dir > 0)
+ parsed[out] = INSTRUCTION (RIGHT, 0, dir);
+ else
+ parsed[out] = INSTRUCTION (LEFT, 0, -dir);
+ }
+ parsed_len = out;
+
+ debug_dump ("bf-pre-incdec-unloop.txt", parsed, parsed_len);
+
+ // Try to eliminate loops that eat a cell and add/subtract its value
+ // to/from some other cell
+ for (in = 0, out = 0; in < parsed_len; in++, out++)
+ {
+ parsed[out] = parsed[in];
+ if (parsed[in].cmd != BEGIN)
+ continue;
+
+ bool ok = false;
+ size_t count = 0;
+ for (size_t k = in + 1; k < parsed_len; k++)
+ {
+ if (parsed[k].cmd == END)
+ {
+ ok = true;
+ break;
+ }
+ if (parsed[k].cmd != INC
+ && parsed[k].cmd != DEC)
+ break;
+ count++;
+ }
+ if (!ok)
+ continue;
+
+ // Stable sort operations by their offsets, put [0] first
+ bool sorted;
+ do
+ {
+ sorted = true;
+ for (size_t k = 1; k < count; k++)
+ {
+ if (parsed[in + k].offset == 0)
+ continue;
+ if (parsed[in + k + 1].offset != 0
+ && parsed[in + k].offset <= parsed[in + k + 1].offset)
+ continue;
+
+ struct instruction tmp = parsed[in + k + 1];
+ parsed[in + k + 1] = parsed[in + k];
+ parsed[in + k] = tmp;
+ sorted = false;
+ }
+ }
+ while (!sorted);
+
+ // Abort the optimization on duplicate offsets (complication with [0])
+ for (size_t k = 1; k < count; k++)
+ if (parsed[in + k].offset == parsed[in + k + 1].offset)
+ ok = false;
+ // XXX: can't make the code longer either
+ for (size_t k = 1; k <= count; k++)
+ if (parsed[in + k].arg != 1)
+ ok = false;
+ if (!ok
+ || parsed[in + 1].cmd != DEC
+ || parsed[in + 1].offset != 0)
+ continue;
+
+ int min_safe_left_offset = 0;
+ if (in > 1 && parsed[in - 1].cmd == RIGHT)
+ min_safe_left_offset = -parsed[in - 1].arg;
+
+ bool cond_needed_for_safety = false;
+ for (size_t k = 0; k < count; k++)
+ if (parsed[in + k + 1].offset < min_safe_left_offset)
+ {
+ cond_needed_for_safety = true;
+ break;
+ }
+
+ in++;
+ if (cond_needed_for_safety)
+ out++;
+
+ parsed[out] = INSTRUCTION (EAT, 0, 0);
+ for (size_t k = 1; k < count; k++)
+ parsed[out + k] = INSTRUCTION (parsed[in + k].cmd == INC
+ ? INCACC : DECACC, parsed[in + k].offset, 0);
+
+ in += count;
+ out += count;
+
+ if (cond_needed_for_safety)
+ parsed[out] = INSTRUCTION (END, 0, 0);
+ else
+ out--;
+ }
+ parsed_len = out;
+
+ debug_dump ("bf-optimized.txt", parsed, parsed_len);
+
+// - - Loop pairing - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+ size_t nesting = 0;
+ size_t *stack = xcalloc (sizeof *stack, parsed_len);
+ for (size_t i = 0; i < parsed_len; i++)
+ {
+ switch (parsed[i].cmd)
+ {
+ case BEGIN:
+ stack[nesting++] = i;
+ break;
+ case END:
+ assert (nesting > 0);
+
+ --nesting;
+ parsed[stack[nesting]].arg = i + 1;
+
+ // Looping can be disabled by optimizations
+ if (parsed[i].arg)
+ parsed[i].arg = stack[nesting] + 1;
+ default:
+ break;
+ }
+ }
+ free (stack);
+ assert (nesting == 0);
+
+ debug_dump ("bf-final.txt", parsed, parsed_len);
+
+// - - JIT - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+ // Functions preserve the registers rbx, rsp, rbp, r12, r13, r14, and r15;
+ // while rax, rdi, rsi, rdx, rcx, r8, r9, r10, r11 are scratch registers.
+
+ str_init (&program);
+ size_t *offsets = xcalloc (sizeof *offsets, parsed_len + 1);
+ uint8_t *arith = xcalloc (sizeof *arith, parsed_len);
+
+#define CODE(x) { char t[] = x; str_append_data (&program, t, sizeof t - 1); }
+#define WORD(x) { size_t t = (size_t)(x); str_append_data (&program, &t, 8); }
+#define DWRD(x) { size_t t = (size_t)(x); str_append_data (&program, &t, 4); }
+
+ CODE ("\x48\x89\xF8") // mov rax, rdi
+ CODE ("\x30\xDB") // xor bl, bl
+
+ for (size_t i = 0; i < parsed_len; i++)
+ {
+ offsets[i] = program.len;
+
+ size_t arg = parsed[i].arg;
+ assert (arg <= UINT32_MAX);
+
+ int offset = parsed[i].offset;
+ assert (offset <= INT8_MAX && offset >= INT8_MIN);
+
+ // Don't save what we've just loaded
+ if (parsed[i].cmd == LEFT || parsed[i].cmd == RIGHT)
+ if (i < 2 || i + 1 >= parsed_len
+ || (parsed[i - 2].cmd != LEFT && parsed[i - 2].cmd != RIGHT)
+ || parsed[i - 1].cmd != BEGIN
+ || parsed[i + 1].cmd != END)
+ CODE ("\x88\x18") // mov [rax], bl
+
+ switch (parsed[i].cmd)
+ {
+ case RIGHT:
+ // add rax, "arg" -- optimistic, no boundary checking
+ if (arg > INT8_MAX)
+ { CODE ("\x48\x05") DWRD (arg) }
+ else
+ { CODE ("\x48\x83\xC0") str_append_c (&program, arg); }
+ break;
+ case LEFT:
+ // sub rax, "arg" -- optimistic, no boundary checking
+ if (arg > INT8_MAX)
+ { CODE ("\x48\x2D") DWRD (arg) }
+ else
+ { CODE ("\x48\x83\xE8") str_append_c (&program, arg); }
+ break;
+
+ case EAT:
+ CODE ("\x41\x88\xDC") // mov r12b, bl
+ CODE ("\x30\xDB") // xor bl, bl
+ arith[i] = 1;
+ break;
+ case INCACC:
+ if (offset)
+ {
+ CODE ("\x44\x00\x60") // add [rax+"offset"], r12b
+ str_append_c (&program, offset);
+ }
+ else
+ {
+ CODE ("\x44\x00\xE3") // add bl, r12b
+ arith[i] = 1;
+ }
+ break;
+ case DECACC:
+ if (offset)
+ {
+ CODE ("\x44\x28\x60") // sub [rax+"offset"], r12b
+ str_append_c (&program, offset);
+ }
+ else
+ {
+ CODE ("\x44\x28\xE3") // sub bl, r12b
+ arith[i] = 1;
+ }
+ break;
+
+ case INC:
+ if (offset)
+ {
+ CODE ("\x80\x40") // add byte [rax+"offset"], "arg"
+ str_append_c (&program, offset);
+ }
+ else
+ {
+ arith[i] = 1;
+ CODE ("\x80\xC3") // add bl, "arg"
+ }
+ str_append_c (&program, arg);
+ break;
+ case DEC:
+ if (offset)
+ {
+ CODE ("\x80\x68") // sub byte [rax+"offset"], "arg"
+ str_append_c (&program, offset);
+ }
+ else
+ {
+ arith[i] = 1;
+ CODE ("\x80\xEB") // sub bl, "arg"
+ }
+ str_append_c (&program, arg);
+ break;
+ case SET:
+ if (offset)
+ {
+ CODE ("\xC6\x40") // mov byte [rax+"offset"], "arg"
+ str_append_c (&program, offset);
+ }
+ else
+ CODE ("\xB3") // mov bl, "arg"
+ str_append_c (&program, arg);
+ break;
+
+ case OUT:
+ CODE ("\x50\x53") // push rax, push rbx
+ CODE ("\x48\x0F\xB6\xFB") // movzx rdi, bl
+ CODE ("\x48\xBE") WORD (stdout) // mov rsi, "stdout"
+ CODE ("\x48\xB8") WORD (fputc) // mov rax, "fputc"
+ CODE ("\xFF\xD0") // call rax
+ CODE ("\x5B\x58") // pop rbx, pop rax
+ break;
+ case IN:
+ CODE ("\x50") // push rax
+ CODE ("\x48\xB8") WORD (cin) // mov rax, "cin"
+ CODE ("\xFF\xD0") // call rax
+ CODE ("\x88\xC3") // mov bl, al
+ CODE ("\x58") // pop rax
+ break;
+
+ case BEGIN:
+ // Don't test the register when the flag has been set already;
+ // this doesn't have much of an effect in practice
+ if (!i || !arith[i - 1])
+ CODE ("\x84\xDB") // test bl, bl
+ CODE ("\x0F\x84\x00\x00\x00\x00") // jz "offsets[i]"
+ break;
+ case END:
+ // We know that the cell is zero, make this an "if", not a "loop";
+ // this doesn't have much of an effect in practice
+ if (!arg)
+ break;
+
+ if (!i || !arith[i - 1])
+ CODE ("\x84\xDB") // test bl, bl
+ CODE ("\x0F\x85\x00\x00\x00\x00") // jnz "offsets[i]"
+ break;
+ }
+
+ // No sense in reading it out when we overwrite it immediately;
+ // this doesn't have much of an effect in practice
+ if (parsed[i].cmd == LEFT || parsed[i].cmd == RIGHT)
+ if (i + 1 >= parsed_len
+ || parsed[i + 1].cmd != SET
+ || parsed[i + 1].offset != 0)
+ CODE ("\x8A\x18") // mov bl, [rax]
+ }
+ // When there is a loop at the end we need to be able to jump past it
+ offsets[parsed_len] = program.len;
+ str_append_c (&program, '\xC3'); // ret
+
+ // Now that we know where each instruction is, fill in relative jumps;
+ // this must accurately reflect code generators for BEGIN and END
+ for (size_t i = 0; i < parsed_len; i++)
+ {
+ if ((parsed[i].cmd != BEGIN && parsed[i].cmd != END)
+ || !parsed[i].arg)
+ continue;
+
+ size_t fixup = offsets[i] + 2;
+ if (!i || !arith[i - 1])
+ fixup += 2;
+
+ *(int32_t *)(program.str + fixup) =
+ ((intptr_t)(offsets[parsed[i].arg]) - (intptr_t)(fixup + 4));
+ }
+ free (offsets);
+ free (arith);
+
+#ifdef DEBUG
+ FILE *bin = fopen ("bf-jit.bin", "w");
+ fwrite (program.str, program.len, 1, bin);
+ fclose (bin);
+#endif
+
+// - - Runtime - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+ // Some systems may have W^X
+ void *executable = mmap (NULL, program.len, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ if (!executable)
+ exit_fatal ("mmap: %s\n", strerror (errno));
+
+ memcpy (executable, program.str, program.len);
+ if (mprotect (executable, program.len, PROT_READ | PROT_EXEC))
+ exit_fatal ("mprotect: %s\n", strerror (errno));
+
+ // We create crash zones on both ends of the tape for some minimum safety
+ long pagesz = sysconf (_SC_PAGESIZE);
+ assert (pagesz > 0);
+
+ const size_t tape_len = (1 << 20) + 2 * pagesz;
+ char *tape = mmap (NULL, tape_len, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ if (!tape)
+ exit_fatal ("mmap: %s\n", strerror (errno));
+
+ memset (tape, 0, tape_len);
+ if (mprotect (tape, pagesz, PROT_NONE)
+ || mprotect (tape + tape_len - pagesz, pagesz, PROT_NONE))
+ exit_fatal ("mprotect: %s\n", strerror (errno));
+
+ ((void (*) (char *)) executable)(tape + pagesz);
+ return 0;
+}
diff --git a/interpreters/bf-jit-unsafe.c b/interpreters/bf-jit-unsafe.c
new file mode 100644
index 0000000..63fbd7e
--- /dev/null
+++ b/interpreters/bf-jit-unsafe.c
@@ -0,0 +1,495 @@
+// This is an exercise in futility more than anything else
+#define _GNU_SOURCE
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <assert.h>
+#include <errno.h>
+
+#if (defined __x86_64__ || defined __amd64__) && defined __unix__
+ #include <unistd.h>
+ #include <sys/mman.h>
+#else
+ #error Platform not supported
+#endif
+
+#define exit_fatal(...) \
+ do { \
+ fprintf (stderr, "fatal: " __VA_ARGS__); \
+ exit (EXIT_FAILURE); \
+ } while (0)
+
+// --- Safe memory management --------------------------------------------------
+
+static void *
+xcalloc (size_t m, size_t n)
+{
+ void *p = calloc (m, n);
+ if (!p)
+ exit_fatal ("calloc: %s\n", strerror (errno));
+ return p;
+}
+
+static void *
+xrealloc (void *o, size_t n)
+{
+ void *p = realloc (o, n);
+ if (!p && n)
+ exit_fatal ("realloc: %s\n", strerror (errno));
+ return p;
+}
+
+// --- Dynamically allocated strings -------------------------------------------
+
+struct str
+{
+ char *str; ///< String data, null terminated
+ size_t alloc; ///< How many bytes are allocated
+ size_t len; ///< How long the string actually is
+};
+
+static void
+str_init (struct str *self)
+{
+ self->len = 0;
+ self->str = xcalloc (1, (self->alloc = 16));
+}
+
+static void
+str_ensure_space (struct str *self, size_t n)
+{
+ // We allocate at least one more byte for the terminating null character
+ size_t new_alloc = self->alloc;
+ while (new_alloc <= self->len + n)
+ new_alloc <<= 1;
+ if (new_alloc != self->alloc)
+ self->str = xrealloc (self->str, (self->alloc = new_alloc));
+}
+
+static void
+str_append_data (struct str *self, const void *data, size_t n)
+{
+ str_ensure_space (self, n);
+ memcpy (self->str + self->len, data, n);
+ self->str[self->len += n] = '\0';
+}
+
+static void
+str_append_c (struct str *self, char c)
+{
+ str_append_data (self, &c, 1);
+}
+
+// --- Application -------------------------------------------------------------
+
+enum command { RIGHT, LEFT, INC, DEC, SET, IN, OUT, BEGIN, END,
+ EAT, INCACC, DECACC };
+bool grouped[] = { 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0 };
+struct instruction { enum command cmd; size_t arg; };
+#define INSTRUCTION(c, a) (struct instruction) { (c), (a) }
+
+// - - Callbacks - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+FILE *input; ///< User input
+
+static int
+cin (void)
+{
+ int c = fgetc (input);
+ assert (c != EOF);
+ return c;
+}
+
+// - - Main - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+#ifdef DEBUG
+static void
+debug_dump (const char *filename, struct instruction *in, size_t len)
+{
+ FILE *fp = fopen (filename, "w");
+ long indent = 0;
+ for (size_t i = 0; i < len; i++)
+ {
+ if (in[i].cmd == END)
+ indent--;
+ for (long k = 0; k < indent; k++)
+ fprintf (fp, " ");
+
+ switch (in[i].cmd)
+ {
+ case RIGHT: fprintf (fp, "RIGHT %zu\n", in[i].arg); break;
+ case LEFT: fprintf (fp, "LEFT %zu\n", in[i].arg); break;
+ case INC: fprintf (fp, "INC %zu\n", in[i].arg); break;
+ case DEC: fprintf (fp, "DEC %zu\n", in[i].arg); break;
+ case OUT: fprintf (fp, "OUT %zu\n", in[i].arg); break;
+ case IN: fprintf (fp, "IN %zu\n", in[i].arg); break;
+ case BEGIN: fprintf (fp, "BEGIN %zu\n", in[i].arg); break;
+ case END: fprintf (fp, "END %zu\n", in[i].arg); break;
+ case SET: fprintf (fp, "SET %zu\n", in[i].arg); break;
+ case EAT: fprintf (fp, "EAT %zu\n", in[i].arg); break;
+ case INCACC: fprintf (fp, "INCACC %zu\n", in[i].arg); break;
+ case DECACC: fprintf (fp, "DECACC %zu\n", in[i].arg); break;
+ }
+ if (in[i].cmd == BEGIN)
+ indent++;
+ }
+ fclose (fp);
+}
+#else
+#define debug_dump(...)
+#endif
+
+int
+main (int argc, char *argv[])
+{
+ (void) argc;
+ (void) argv;
+
+ struct str program;
+ str_init (&program);
+
+ int c;
+ while ((c = fgetc (stdin)) != EOF)
+ str_append_c (&program, c);
+ if (ferror (stdin))
+ exit_fatal ("can't read program\n");
+ if (!(input = fopen ("/dev/tty", "rb")))
+ exit_fatal ("can't open terminal for reading\n");
+
+// - - Decode and group - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+ struct instruction *parsed = xcalloc (sizeof *parsed, program.len);
+ size_t parsed_len = 0;
+
+ for (size_t i = 0; i < program.len; i++)
+ {
+ enum command cmd;
+ switch (program.str[i])
+ {
+ case '>': cmd = RIGHT; break;
+ case '<': cmd = LEFT; break;
+ case '+': cmd = INC; break;
+ case '-': cmd = DEC; break;
+ case '.': cmd = OUT; break;
+ case ',': cmd = IN; break;
+ case '[': cmd = BEGIN; break;
+ case ']': cmd = END; break;
+ default: continue;
+ }
+
+ // The most basic optimization is to group identical commands together
+ if (!parsed_len || !grouped[cmd] || parsed[parsed_len - 1].cmd != cmd)
+ parsed_len++;
+
+ parsed[parsed_len - 1].cmd = cmd;
+ parsed[parsed_len - 1].arg++;
+ }
+
+// - - Optimization passes - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+ debug_dump ("bf-no-opt.txt", parsed, parsed_len);
+
+ size_t in = 0, out = 0;
+ for (; in < parsed_len; in++, out++)
+ {
+ // This shows up in mandelbrot.bf a lot but actually helps hanoi.bf
+ if (in + 5 < parsed_len
+ && parsed[in].cmd == BEGIN && parsed[in + 5].cmd == END
+ && parsed[in + 1].cmd == DEC && parsed[in + 1].arg == 1
+
+ && parsed[in + 2].cmd == LEFT && parsed[in + 4].cmd == RIGHT
+ && parsed[in + 2].arg == parsed[in + 4].arg
+
+ && (parsed[in + 3].cmd == INC || parsed[in + 3].cmd == DEC)
+ && parsed[in + 3].arg == 1)
+ {
+ // This mustn't make the move when the cell is zero already
+ parsed[out] = parsed[in];
+ parsed[out + 1] = INSTRUCTION (EAT, 0);
+ parsed[out + 2] = parsed[in + 2];
+ parsed[out + 3] = INSTRUCTION
+ (parsed[in + 3].cmd == INC ? INCACC : DECACC, 0);
+ parsed[out + 4] = parsed[in + 4];
+ // This disables the looping further in the code;
+ // this doesn't have much of an effect in practice
+ parsed[out + 5] = INSTRUCTION (END, 0);
+ in += 5;
+ out += 5;
+ }
+ // The simpler case that cannot crash and thus can avoid the loop
+ else if (in + 5 < parsed_len
+ && parsed[in].cmd == BEGIN && parsed[in + 5].cmd == END
+ && parsed[in + 1].cmd == DEC && parsed[in + 1].arg == 1
+
+ && parsed[in + 2].cmd == RIGHT && parsed[in + 4].cmd == LEFT
+ && parsed[in + 2].arg == parsed[in + 4].arg
+
+ && (parsed[in + 3].cmd == INC || parsed[in + 3].cmd == DEC)
+ && parsed[in + 3].arg == 1)
+ {
+ parsed[out] = INSTRUCTION (EAT, 0);
+ parsed[out + 1] = parsed[in + 2];
+ parsed[out + 2] = INSTRUCTION
+ (parsed[in + 3].cmd == INC ? INCACC : DECACC, 0);
+ parsed[out + 3] = parsed[in + 4];
+ in += 5;
+ out += 3;
+ }
+ else if (in + 2 < parsed_len
+ && parsed[in ].cmd == BEGIN
+ && parsed[in + 1].cmd == DEC && parsed[in + 1].arg == 1
+ && parsed[in + 2].cmd == END)
+ {
+ parsed[out] = INSTRUCTION (SET, 0);
+ in += 2;
+ }
+ else if (out && parsed[out - 1].cmd == SET && parsed[in].cmd == INC)
+ parsed[--out].arg += parsed[in].arg;
+ else if (out != in)
+ parsed[out] = parsed[in];
+ }
+ parsed_len = out;
+
+ for (in = 0, out = 0; in < parsed_len; in++, out++)
+ {
+ ssize_t dir = 0;
+ if (parsed[in].cmd == RIGHT)
+ dir = parsed[in].arg;
+ else if (parsed[in].cmd == LEFT)
+ dir = -(ssize_t) parsed[in].arg;
+ else
+ {
+ parsed[out] = parsed[in];
+ continue;
+ }
+
+ for (; in + 1 < parsed_len; in++)
+ {
+ if (parsed[in + 1].cmd == RIGHT)
+ dir += parsed[in + 1].arg;
+ else if (parsed[in + 1].cmd == LEFT)
+ dir -= (ssize_t) parsed[in + 1].arg;
+ else
+ break;
+ }
+
+ if (!dir)
+ out--;
+ else if (dir > 0)
+ parsed[out] = INSTRUCTION (RIGHT, dir);
+ else
+ parsed[out] = INSTRUCTION (LEFT, -dir);
+ }
+ parsed_len = out;
+
+ debug_dump ("bf-optimized.txt", parsed, parsed_len);
+
+// - - Loop pairing - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+ size_t nesting = 0;
+ size_t *stack = xcalloc (sizeof *stack, parsed_len);
+ for (size_t i = 0; i < parsed_len; i++)
+ {
+ switch (parsed[i].cmd)
+ {
+ case BEGIN:
+ stack[nesting++] = i;
+ break;
+ case END:
+ assert (nesting > 0);
+
+ --nesting;
+ parsed[stack[nesting]].arg = i + 1;
+
+ // Looping can be disabled by optimizations
+ if (parsed[i].arg)
+ parsed[i].arg = stack[nesting] + 1;
+ default:
+ break;
+ }
+ }
+ free (stack);
+ assert (nesting == 0);
+
+ debug_dump ("bf-final.txt", parsed, parsed_len);
+
+// - - JIT - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+ // Functions preserve the registers rbx, rsp, rbp, r12, r13, r14, and r15;
+ // while rax, rdi, rsi, rdx, rcx, r8, r9, r10, r11 are scratch registers.
+
+ str_init (&program);
+ size_t *offsets = xcalloc (sizeof *offsets, parsed_len + 1);
+ uint8_t *arith = xcalloc (sizeof *arith, parsed_len);
+
+#define CODE(x) { char t[] = x; str_append_data (&program, t, sizeof t - 1); }
+#define WORD(x) { size_t t = (size_t)(x); str_append_data (&program, &t, 8); }
+#define DWRD(x) { size_t t = (size_t)(x); str_append_data (&program, &t, 4); }
+
+ CODE ("\x48\x89\xF8") // mov rax, rdi
+ CODE ("\x30\xDB") // xor bl, bl
+
+ for (size_t i = 0; i < parsed_len; i++)
+ {
+ offsets[i] = program.len;
+
+ size_t arg = parsed[i].arg;
+ assert (arg <= UINT32_MAX);
+
+ // Don't save what we've just loaded
+ if (parsed[i].cmd == LEFT || parsed[i].cmd == RIGHT)
+ if (i < 2 || i + 1 >= parsed_len
+ || (parsed[i - 2].cmd != LEFT && parsed[i - 2].cmd != RIGHT)
+ || parsed[i - 1].cmd != BEGIN
+ || parsed[i + 1].cmd != END)
+ CODE ("\x88\x18") // mov [rax], bl
+
+ switch (parsed[i].cmd)
+ {
+ case RIGHT:
+ // add rax, "arg" -- optimistic, no boundary checking
+ if (arg > INT8_MAX)
+ { CODE ("\x48\x05") DWRD (arg) }
+ else
+ { CODE ("\x48\x83\xC0") str_append_c (&program, arg); }
+ break;
+ case LEFT:
+ // sub rax, "arg" -- optimistic, no boundary checking
+ if (arg > INT8_MAX)
+ { CODE ("\x48\x2D") DWRD (arg) }
+ else
+ { CODE ("\x48\x83\xE8") str_append_c (&program, arg); }
+ break;
+
+ case EAT:
+ CODE ("\x41\x88\xDC") // mov r12b, bl
+ CODE ("\x30\xDB") // xor bl, bl
+ arith[i] = 1;
+ break;
+ case INCACC:
+ CODE ("\x44\x00\xE3") // add bl, r12b
+ arith[i] = 1;
+ break;
+ case DECACC:
+ CODE ("\x44\x28\xE3") // sub bl, r12b
+ arith[i] = 1;
+ break;
+
+ case INC:
+ CODE ("\x80\xC3") // add bl, "arg"
+ str_append_c (&program, arg);
+ arith[i] = 1;
+ break;
+ case DEC:
+ CODE ("\x80\xEB") // sub bl, "arg"
+ str_append_c (&program, arg);
+ arith[i] = 1;
+ break;
+ case SET:
+ CODE ("\xB3") // mov bl, "arg"
+ str_append_c (&program, arg);
+ break;
+
+ case OUT:
+ CODE ("\x50\x53") // push rax, push rbx
+ CODE ("\x48\x0F\xB6\xFB") // movzx rdi, bl
+ CODE ("\x48\xBE") WORD (stdout) // mov rsi, "stdout"
+ CODE ("\x48\xB8") WORD (fputc) // mov rax, "fputc"
+ CODE ("\xFF\xD0") // call rax
+ CODE ("\x5B\x58") // pop rbx, pop rax
+ break;
+ case IN:
+ CODE ("\x50") // push rax
+ CODE ("\x48\xB8") WORD (cin) // mov rax, "cin"
+ CODE ("\xFF\xD0") // call rax
+ CODE ("\x88\xC3") // mov bl, al
+ CODE ("\x58") // pop rax
+ break;
+
+ case BEGIN:
+ // Don't test the register when the flag has been set already;
+ // this doesn't have much of an effect in practice
+ if (!i || !arith[i - 1])
+ CODE ("\x84\xDB") // test bl, bl
+ CODE ("\x0F\x84\x00\x00\x00\x00") // jz "offsets[i]"
+ break;
+ case END:
+ // We know that the cell is zero, make this an "if", not a "loop";
+ // this doesn't have much of an effect in practice
+ if (!arg)
+ break;
+
+ if (!i || !arith[i - 1])
+ CODE ("\x84\xDB") // test bl, bl
+ CODE ("\x0F\x85\x00\x00\x00\x00") // jnz "offsets[i]"
+ break;
+ }
+
+ // No sense in reading it out when we overwrite it immediately;
+ // this doesn't have much of an effect in practice
+ if (parsed[i].cmd == LEFT || parsed[i].cmd == RIGHT)
+ if (i + 1 >= parsed_len
+ || parsed[i + 1].cmd != SET)
+ CODE ("\x8A\x18") // mov bl, [rax]
+ }
+ // When there is a loop at the end we need to be able to jump past it
+ offsets[parsed_len] = program.len;
+ str_append_c (&program, '\xC3'); // ret
+
+ // Now that we know where each instruction is, fill in relative jumps;
+ // this must accurately reflect code generators for BEGIN and END
+ for (size_t i = 0; i < parsed_len; i++)
+ {
+ if ((parsed[i].cmd != BEGIN && parsed[i].cmd != END)
+ || !parsed[i].arg)
+ continue;
+
+ size_t fixup = offsets[i] + 2;
+ if (!i || !arith[i - 1])
+ fixup += 2;
+
+ *(int32_t *)(program.str + fixup) =
+ ((intptr_t)(offsets[parsed[i].arg]) - (intptr_t)(fixup + 4));
+ }
+ free (offsets);
+ free (arith);
+
+#ifdef DEBUG
+ FILE *bin = fopen ("bf-jit.bin", "w");
+ fwrite (program.str, program.len, 1, bin);
+ fclose (bin);
+#endif
+
+// - - Runtime - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+ // Some systems may have W^X
+ void *executable = mmap (NULL, program.len, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ if (!executable)
+ exit_fatal ("mmap: %s\n", strerror (errno));
+
+ memcpy (executable, program.str, program.len);
+ if (mprotect (executable, program.len, PROT_READ | PROT_EXEC))
+ exit_fatal ("mprotect: %s\n", strerror (errno));
+
+ // We create crash zones on both ends of the tape for some minimum safety
+ long pagesz = sysconf (_SC_PAGESIZE);
+ assert (pagesz > 0);
+
+ const size_t tape_len = (1 << 20) + 2 * pagesz;
+ char *tape = mmap (NULL, tape_len, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ if (!tape)
+ exit_fatal ("mmap: %s\n", strerror (errno));
+
+ memset (tape, 0, tape_len);
+ if (mprotect (tape, pagesz, PROT_NONE)
+ || mprotect (tape + tape_len - pagesz, pagesz, PROT_NONE))
+ exit_fatal ("mprotect: %s\n", strerror (errno));
+
+ ((void (*) (char *)) executable)(tape + pagesz);
+ return 0;
+}
diff --git a/interpreters/bf-jit.c b/interpreters/bf-jit.c
new file mode 100644
index 0000000..0be6d94
--- /dev/null
+++ b/interpreters/bf-jit.c
@@ -0,0 +1,327 @@
+// This is an exercise in futility more than anything else
+#define _GNU_SOURCE
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <assert.h>
+#include <errno.h>
+
+#if (defined __x86_64__ || defined __amd64__) && defined __unix__
+ #include <sys/mman.h>
+#else
+ #error Platform not supported
+#endif
+
+#define exit_fatal(...) \
+ do { \
+ fprintf (stderr, "fatal: " __VA_ARGS__); \
+ exit (EXIT_FAILURE); \
+ } while (0)
+
+// --- Safe memory management --------------------------------------------------
+
+static void *
+xcalloc (size_t m, size_t n)
+{
+ void *p = calloc (m, n);
+ if (!p)
+ exit_fatal ("calloc: %s\n", strerror (errno));
+ return p;
+}
+
+static void *
+xrealloc (void *o, size_t n)
+{
+ void *p = realloc (o, n);
+ if (!p && n)
+ exit_fatal ("realloc: %s\n", strerror (errno));
+ return p;
+}
+
+// --- Dynamically allocated strings -------------------------------------------
+
+struct str
+{
+ char *str; ///< String data, null terminated
+ size_t alloc; ///< How many bytes are allocated
+ size_t len; ///< How long the string actually is
+};
+
+static void
+str_init (struct str *self)
+{
+ self->len = 0;
+ self->str = xcalloc (1, (self->alloc = 16));
+}
+
+static void
+str_ensure_space (struct str *self, size_t n)
+{
+ // We allocate at least one more byte for the terminating null character
+ size_t new_alloc = self->alloc;
+ while (new_alloc <= self->len + n)
+ new_alloc <<= 1;
+ if (new_alloc != self->alloc)
+ self->str = xrealloc (self->str, (self->alloc = new_alloc));
+}
+
+static void
+str_append_data (struct str *self, const void *data, size_t n)
+{
+ str_ensure_space (self, n);
+ memcpy (self->str + self->len, data, n);
+ self->str[self->len += n] = '\0';
+}
+
+static void
+str_append_c (struct str *self, char c)
+{
+ str_append_data (self, &c, 1);
+}
+
+// --- Application -------------------------------------------------------------
+
+struct str data; ///< Data tape
+volatile size_t dataptr; ///< Current location on the tape
+FILE *input; ///< User input
+
+enum command { RIGHT, LEFT, INC, DEC, SET, IN, OUT, BEGIN, END };
+bool grouped[] = { 1, 1, 1, 1, 1, 0, 0, 0, 0 };
+struct instruction { enum command cmd; size_t arg; };
+
+// - - Callbacks - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+// Some things I just really don't want to write in assembly even though it
+// is effectively a big performance hit, eliminating the advantage of JIT
+
+static void
+right (size_t arg)
+{
+ assert (SIZE_MAX - dataptr > arg);
+ dataptr += arg;
+
+ while (dataptr >= data.len)
+ str_append_c (&data, 0);
+}
+
+static void
+left (size_t arg)
+{
+ assert (dataptr >= arg);
+ dataptr -= arg;
+}
+
+static int
+cin (void)
+{
+ int c = fgetc (input);
+ assert (c != EOF);
+ return c;
+}
+
+// - - Main - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+int
+main (int argc, char *argv[])
+{
+ (void) argc;
+ (void) argv;
+
+ struct str program;
+ str_init (&program);
+
+ int c;
+ while ((c = fgetc (stdin)) != EOF)
+ str_append_c (&program, c);
+ if (ferror (stdin))
+ exit_fatal ("can't read program\n");
+ if (!(input = fopen ("/dev/tty", "rb")))
+ exit_fatal ("can't open terminal for reading\n");
+
+// - - Decode and group - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+ struct instruction *parsed = xcalloc (sizeof *parsed, program.len);
+ size_t parsed_len = 0;
+
+ for (size_t i = 0; i < program.len; i++)
+ {
+ enum command cmd;
+ switch (program.str[i])
+ {
+ case '>': cmd = RIGHT; break;
+ case '<': cmd = LEFT; break;
+ case '+': cmd = INC; break;
+ case '-': cmd = DEC; break;
+ case '.': cmd = OUT; break;
+ case ',': cmd = IN; break;
+ case '[': cmd = BEGIN; break;
+ case ']': cmd = END; break;
+ default: continue;
+ }
+
+ if (!parsed_len || !grouped[cmd] || parsed[parsed_len - 1].cmd != cmd)
+ parsed_len++;
+
+ parsed[parsed_len - 1].cmd = cmd;
+ parsed[parsed_len - 1].arg++;
+ }
+
+// - - Simple optimization pass - - - - - - - - - - - - - - - - - - - - - - - -
+
+ size_t in = 0, out = 0;
+ for (; in < parsed_len; in++, out++)
+ {
+ if (in + 2 < parsed_len
+ && parsed[in ].cmd == BEGIN
+ && parsed[in + 1].cmd == DEC && parsed[in + 1].arg == 1
+ && parsed[in + 2].cmd == END)
+ {
+ parsed[out].cmd = SET;
+ parsed[out].arg = 0;
+ in += 2;
+ }
+ else if (out && parsed[out - 1].cmd == SET && parsed[in].cmd == INC)
+ parsed[--out].arg += parsed[in].arg;
+ else if (out != in)
+ parsed[out] = parsed[in];
+ }
+
+ parsed_len = out;
+
+// - - Loop pairing - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+ size_t nesting = 0;
+ size_t *stack = xcalloc (sizeof *stack, parsed_len);
+ for (size_t i = 0; i < parsed_len; i++)
+ {
+ switch (parsed[i].cmd)
+ {
+ case BEGIN:
+ stack[nesting++] = i;
+ break;
+ case END:
+ assert (nesting > 0);
+
+ --nesting;
+ parsed[stack[nesting]].arg = i + 1;
+ parsed[i].arg = stack[nesting] + 1;
+ default:
+ break;
+ }
+ }
+ free (stack);
+ assert (nesting == 0);
+
+// - - JIT - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+ // Functions preserve the registers rbx, rsp, rbp, r12, r13, r14, and r15;
+ // while rax, rdi, rsi, rdx, rcx, r8, r9, r10, r11 are scratch registers.
+
+ str_init (&program);
+ size_t *offsets = xcalloc (sizeof *offsets, parsed_len + 1);
+
+#define CODE(x) { char t[] = x; str_append_data (&program, t, sizeof t - 1); }
+#define WORD(x) { size_t t = (size_t)(x); str_append_data (&program, &t, 8); }
+
+ CODE ("\x49\xBD") WORD (&dataptr) // mov r13, qword "&dataptr"
+ CODE ("\x49\xBF") WORD (&data.str) // mov r15, qword "&data.str"
+ CODE ("\x4D\x8B\x37") // mov r14, qword [r15]
+ CODE ("\x30\xDB") // xor bl, bl
+
+ for (size_t i = 0; i < parsed_len; i++)
+ {
+ offsets[i] = program.len;
+
+ size_t arg = parsed[i].arg;
+ switch (parsed[i].cmd)
+ {
+ case RIGHT:
+ CODE ("\x41\x88\x1E") // mov [r14], bl
+ CODE ("\x48\xBF") WORD (arg) // mov rdi, "arg"
+ CODE ("\x48\xB8") WORD (right) // mov rax, "right"
+ CODE ("\xFF\xD0") // call rax
+
+ // The data could get reallocated, so reload the address
+ CODE ("\x4D\x8B\x37") // mov r14, qword [r15]
+ CODE ("\x4D\x03\x75\x00") // add r14, [r13]
+ CODE ("\x41\x8A\x1E") // mov bl, [r14]
+ break;
+ case LEFT:
+ CODE ("\x41\x88\x1E") // mov [r14], bl
+ CODE ("\x48\xBF") WORD (arg) // mov rdi, "arg"
+ CODE ("\x49\x29\xFE") // sub r14, rdi -- optimistic
+ CODE ("\x48\xB8") WORD (left) // mov rax, "left"
+ CODE ("\xFF\xD0") // call rax
+ CODE ("\x41\x8A\x1E") // mov bl, [r14]
+ break;
+
+ case INC:
+ CODE ("\x80\xC3") // add bl, "arg"
+ str_append_c (&program, arg);
+ break;
+ case DEC:
+ CODE ("\x80\xEB") // sub bl, "arg"
+ str_append_c (&program, arg);
+ break;
+ case SET:
+ CODE ("\xB3") // mov bl, "arg"
+ str_append_c (&program, arg);
+ break;
+
+ case OUT:
+ CODE ("\x48\x0F\xB6\xFB") // movzx rdi, bl
+ CODE ("\x48\xBE") WORD (stdout) // mov rsi, "stdout"
+ CODE ("\x48\xB8") WORD (fputc) // mov rax, "fputc"
+ CODE ("\xFF\xD0") // call rax
+ break;
+ case IN:
+ CODE ("\x48\xB8") WORD (cin) // mov rax, "cin"
+ CODE ("\xFF\xD0") // call rax
+ CODE ("\x88\xC3") // mov bl, al
+ break;
+
+ case BEGIN:
+ CODE ("\x84\xDB") // test bl, bl
+ CODE ("\x0F\x84\x00\x00\x00\x00") // jz "offsets[i]"
+ break;
+ case END:
+ CODE ("\x84\xDB") // test bl, bl
+ CODE ("\x0F\x85\x00\x00\x00\x00") // jnz "offsets[i]"
+ break;
+ }
+ }
+ // When there is a loop at the end we need to be able to jump past it
+ offsets[parsed_len] = program.len;
+ str_append_c (&program, '\xC3'); // ret
+
+ // Now that we know where each instruction is, fill in relative jumps
+ for (size_t i = 0; i < parsed_len; i++)
+ {
+ if (parsed[i].cmd != BEGIN && parsed[i].cmd != END)
+ continue;
+ size_t fixup = offsets[i] + 4;
+ *(int32_t *)(program.str + fixup) =
+ ((intptr_t)(offsets[parsed[i].arg]) - (intptr_t)(fixup + 4));
+ }
+ free (offsets);
+
+// - - Runtime - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+ // Some systems may have W^X
+ void *executable = mmap (NULL, program.len, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ if (!executable)
+ exit_fatal ("mmap: %s\n", strerror (errno));
+
+ memcpy (executable, program.str, program.len);
+ if (mprotect (executable, program.len, PROT_READ | PROT_EXEC))
+ exit_fatal ("mprotect: %s\n", strerror (errno));
+
+ str_init (&data);
+ str_append_c (&data, 0);
+ ((void (*) (void)) executable)();
+ return 0;
+}
diff --git a/interpreters/bf-optimizing.c b/interpreters/bf-optimizing.c
new file mode 100644
index 0000000..b37c0f2
--- /dev/null
+++ b/interpreters/bf-optimizing.c
@@ -0,0 +1,213 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <assert.h>
+#include <errno.h>
+
+#define exit_fatal(...) \
+ do { \
+ fprintf (stderr, "fatal: " __VA_ARGS__); \
+ exit (EXIT_FAILURE); \
+ } while (0)
+
+// --- Safe memory management --------------------------------------------------
+
+static void *
+xcalloc (size_t m, size_t n)
+{
+ void *p = calloc (m, n);
+ if (!p)
+ exit_fatal ("calloc: %s\n", strerror (errno));
+ return p;
+}
+
+static void *
+xrealloc (void *o, size_t n)
+{
+ void *p = realloc (o, n);
+ if (!p && n)
+ exit_fatal ("realloc: %s\n", strerror (errno));
+ return p;
+}
+
+// --- Dynamically allocated strings -------------------------------------------
+
+struct str
+{
+ char *str; ///< String data, null terminated
+ size_t alloc; ///< How many bytes are allocated
+ size_t len; ///< How long the string actually is
+};
+
+static void
+str_init (struct str *self)
+{
+ self->len = 0;
+ self->str = xcalloc (1, (self->alloc = 16));
+}
+
+static void
+str_ensure_space (struct str *self, size_t n)
+{
+ // We allocate at least one more byte for the terminating null character
+ size_t new_alloc = self->alloc;
+ while (new_alloc <= self->len + n)
+ new_alloc <<= 1;
+ if (new_alloc != self->alloc)
+ self->str = xrealloc (self->str, (self->alloc = new_alloc));
+}
+
+static void
+str_append_data (struct str *self, const void *data, size_t n)
+{
+ str_ensure_space (self, n);
+ memcpy (self->str + self->len, data, n);
+ self->str[self->len += n] = '\0';
+}
+
+static void
+str_append_c (struct str *self, char c)
+{
+ str_append_data (self, &c, 1);
+}
+
+// --- Main --------------------------------------------------------------------
+
+struct str program; ///< Raw program
+struct str data; ///< Data tape
+
+enum command { RIGHT, LEFT, INC, DEC, SET, IN, OUT, BEGIN, END };
+bool grouped[] = { 1, 1, 1, 1, 1, 0, 0, 0, 0 };
+struct instruction { enum command cmd; size_t arg; };
+
+int
+main (int argc, char *argv[])
+{
+ (void) argc; str_init (&program);
+ (void) argv; str_init (&data);
+
+ int c;
+ while ((c = fgetc (stdin)) != EOF)
+ str_append_c (&program, c);
+ if (ferror (stdin))
+ exit_fatal ("can't read program\n");
+
+ FILE *input = fopen ("/dev/tty", "rb");
+ if (!input)
+ exit_fatal ("can't open terminal for reading\n");
+
+// - - Decode and group - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+ struct instruction *parsed = xcalloc (sizeof *parsed, program.len);
+ size_t parsed_len = 0;
+
+ for (size_t i = 0; i < program.len; i++)
+ {
+ enum command cmd;
+ switch (program.str[i])
+ {
+ case '>': cmd = RIGHT; break;
+ case '<': cmd = LEFT; break;
+ case '+': cmd = INC; break;
+ case '-': cmd = DEC; break;
+ case '.': cmd = OUT; break;
+ case ',': cmd = IN; break;
+ case '[': cmd = BEGIN; break;
+ case ']': cmd = END; break;
+ default: continue;
+ }
+
+ if (!parsed_len || !grouped[cmd] || parsed[parsed_len - 1].cmd != cmd)
+ parsed_len++;
+
+ parsed[parsed_len - 1].cmd = cmd;
+ parsed[parsed_len - 1].arg++;
+ }
+
+// - - Simple optimization pass - - - - - - - - - - - - - - - - - - - - - - - -
+
+ size_t in = 0, out = 0;
+ for (; in < parsed_len; in++, out++)
+ {
+ if (in + 2 < parsed_len
+ && parsed[in ].cmd == BEGIN
+ && parsed[in + 1].cmd == DEC && parsed[in + 1].arg == 1
+ && parsed[in + 2].cmd == END)
+ {
+ parsed[out].cmd = SET;
+ parsed[out].arg = 0;
+ in += 2;
+ }
+ else if (out && parsed[out - 1].cmd == SET && parsed[in].cmd == INC)
+ parsed[--out].arg += parsed[in].arg;
+ else if (out != in)
+ parsed[out] = parsed[in];
+ }
+
+ parsed_len = out;
+
+// - - Loop pairing - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+ size_t nesting = 0;
+ size_t *stack = xcalloc (sizeof *stack, parsed_len);
+ for (size_t i = 0; i < parsed_len; i++)
+ {
+ switch (parsed[i].cmd)
+ {
+ case BEGIN:
+ stack[nesting++] = i;
+ break;
+ case END:
+ assert (nesting > 0);
+
+ --nesting;
+ parsed[stack[nesting]].arg = i;
+ parsed[i].arg = stack[nesting];
+ default:
+ break;
+ }
+ }
+ assert (nesting == 0);
+
+// - - Runtime - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+ size_t dataptr = 0;
+ str_append_c (&data, 0);
+
+ for (size_t i = 0; i < parsed_len; i++)
+ {
+ size_t arg = parsed[i].arg;
+ switch (parsed[i].cmd)
+ {
+ case RIGHT:
+ assert (SIZE_MAX - dataptr > arg);
+ dataptr += arg;
+
+ while (dataptr >= data.len)
+ str_append_c (&data, 0);
+ break;
+ case LEFT:
+ assert (dataptr >= arg);
+ dataptr -= arg;
+ break;
+
+ case INC: data.str[dataptr] += arg; break;
+ case DEC: data.str[dataptr] -= arg; break;
+ case SET: data.str[dataptr] = arg; break;
+
+ case OUT:
+ fputc (data.str[dataptr], stdout);
+ break;
+ case IN:
+ data.str[dataptr] = c = fgetc (input);
+ assert (c != EOF);
+ break;
+
+ case BEGIN: if (!data.str[dataptr]) i = arg; break;
+ case END: if ( data.str[dataptr]) i = arg; break;
+ }
+ }
+ return 0;
+}
diff --git a/interpreters/bf.c b/interpreters/bf.c
new file mode 100644
index 0000000..606c609
--- /dev/null
+++ b/interpreters/bf.c
@@ -0,0 +1,160 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h>
+#include <assert.h>
+#include <errno.h>
+
+#define exit_fatal(...) \
+ do { \
+ fprintf (stderr, "fatal: " __VA_ARGS__); \
+ exit (EXIT_FAILURE); \
+ } while (0)
+
+// --- Safe memory management --------------------------------------------------
+
+static void *
+xmalloc (size_t n)
+{
+ void *p = malloc (n);
+ if (!p)
+ exit_fatal ("malloc: %s\n", strerror (errno));
+ return p;
+}
+
+static void *
+xrealloc (void *o, size_t n)
+{
+ void *p = realloc (o, n);
+ if (!p && n)
+ exit_fatal ("realloc: %s\n", strerror (errno));
+ return p;
+}
+
+// --- Dynamically allocated strings -------------------------------------------
+
+struct str
+{
+ char *str; ///< String data, null terminated
+ size_t alloc; ///< How many bytes are allocated
+ size_t len; ///< How long the string actually is
+};
+
+static void
+str_init (struct str *self)
+{
+ self->alloc = 16;
+ self->len = 0;
+ self->str = strcpy (xmalloc (self->alloc), "");
+}
+
+static void
+str_ensure_space (struct str *self, size_t n)
+{
+ // We allocate at least one more byte for the terminating null character
+ size_t new_alloc = self->alloc;
+ while (new_alloc <= self->len + n)
+ new_alloc <<= 1;
+ if (new_alloc != self->alloc)
+ self->str = xrealloc (self->str, (self->alloc = new_alloc));
+}
+
+static void
+str_append_data (struct str *self, const void *data, size_t n)
+{
+ str_ensure_space (self, n);
+ memcpy (self->str + self->len, data, n);
+ self->len += n;
+ self->str[self->len] = '\0';
+}
+
+static void
+str_append_c (struct str *self, char c)
+{
+ str_append_data (self, &c, 1);
+}
+
+// --- Main --------------------------------------------------------------------
+
+int
+main (int argc, char *argv[])
+{
+ struct str program; str_init (&program);
+ struct str data; str_init (&data);
+
+ int c;
+ while ((c = fgetc (stdin)) != EOF)
+ str_append_c (&program, c);
+ if (ferror (stdin))
+ exit_fatal ("can't read program\n");
+
+ FILE *input = fopen ("/dev/tty", "rb");
+ if (!input)
+ exit_fatal ("can't open terminal for reading\n");
+
+ size_t dataptr = 0;
+ str_append_c (&data, 0);
+
+ for (size_t i = 0; i < program.len; i++)
+ {
+ switch (program.str[i])
+ {
+ long pairs;
+ case '>':
+ assert (dataptr != SIZE_MAX);
+ dataptr++;
+ if (dataptr == data.len)
+ str_append_c (&data, 0);
+ break;
+ case '<':
+ assert (dataptr != 0);
+ dataptr--;
+ break;
+
+ case '+': data.str[dataptr]++; break;
+ case '-': data.str[dataptr]--; break;
+
+ case '.':
+ fputc (data.str[dataptr], stdout);
+ break;
+ case ',':
+ data.str[dataptr] = c = fgetc (input);
+ assert (c != EOF);
+ break;
+
+ case '[':
+ if (data.str[dataptr]) break;
+
+ for (pairs = 0; i < program.len; i++)
+ {
+ switch (program.str[i])
+ {
+ case '[': pairs++; break;
+ case ']': pairs--; break;
+ }
+ if (!pairs)
+ break;
+ }
+ assert (!pairs);
+ break;
+ case ']':
+ if (!data.str[dataptr]) break;
+
+ for (pairs = 0; i != SIZE_MAX; i--)
+ {
+ switch (program.str[i])
+ {
+ case '[': pairs--; break;
+ case ']': pairs++; break;
+ }
+ if (!pairs)
+ break;
+ }
+ assert (!pairs);
+ break;
+ default:
+ break;
+ }
+ }
+ return 0;
+}