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-rw-r--r--interpreters/bf-faster-loops.c151
1 files changed, 151 insertions, 0 deletions
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;
+}