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/**
* It would perhaps be more sensible just to store the bits
* as an array of char or similar, but this way is more fun.
* This is a pretty inefficient implementation, althought I
* suspect that won't be a problem.
*/
#include <stdlib.h>
#include <string.h>
#include <limits.h>
#include <assert.h>
#include "bitstream.h"
#define MAX(a, b) ((a) < (b) ? (b) : (a))
#define MIN(a, b) ((a) > (b) ? (b) : (a))
struct bitstream {
size_t pos; /* bits */
size_t count; /* bits */
size_t bufsiz; /* bytes */
unsigned char * buffer;
};
static size_t bits_to_bytes(size_t bits)
{
return (bits / CHAR_BIT) + (bits % CHAR_BIT != 0);
}
static int ensure_available(struct bitstream * stream, size_t bits)
{
size_t need_bits = stream->pos + bits;
size_t need_bytes = need_bits / CHAR_BIT + ((need_bits % CHAR_BIT) ? 0 : 1);
size_t newsize;
if (stream->bufsiz >= need_bytes)
return 0;
newsize = MAX(stream->bufsiz, 100);
while (newsize < need_bytes)
newsize *= 2;
return bitstream_resize(stream, newsize);
}
struct bitstream * bitstream_create(void)
{
struct bitstream * obj;
obj = malloc(sizeof(*obj));
if (obj) {
obj->pos = 0;
obj->count = 0;
obj->bufsiz = 0;
obj->buffer = 0;
}
return obj;
}
int bitstream_resize(struct bitstream * stream, size_t bits)
{
size_t newsize;
void * newbuf;
newsize = bits_to_bytes(bits);
newbuf = realloc(stream->buffer, newsize);
if (newbuf) {
stream->bufsiz = newsize;
stream->buffer = newbuf;
}
return newbuf ? 0 : -1;
}
void bitstream_destroy(struct bitstream * stream)
{
free(stream->buffer);
free(stream);
}
struct bitstream * bitstream_copy(const struct bitstream * src)
{
struct bitstream * ret;
ret = bitstream_create();
if (!ret)
return 0;
if (bitstream_resize(ret, src->count) != 0) {
free(ret);
return 0;
}
ret->pos = src->pos;
ret->count = src->count;
memcpy(ret->buffer, src->buffer, src->bufsiz);
return ret;
}
void bitstream_seek(struct bitstream * stream, size_t pos)
{
assert(pos <= stream->count);
stream->pos = pos;
}
size_t bitstream_tell(const struct bitstream * stream)
{
return stream->pos;
}
size_t bitstream_remaining(const struct bitstream * stream)
{
return stream->count - stream->pos;
}
size_t bitstream_size(const struct bitstream * stream)
{
return stream->count;
}
unsigned int bitstream_read(struct bitstream * stream, size_t bits)
{
unsigned int result = 0;
unsigned char * byte;
size_t bitnum;
assert(bitstream_remaining(stream) >= bits);
byte = stream->buffer + (stream->pos / CHAR_BIT);
bitnum = stream->pos % CHAR_BIT;
stream->pos += bits;
while (bits-- > 0) {
int bit = (*byte >> bitnum++) & 0x1;
result = (result << 1) | bit;
if (bitnum == CHAR_BIT) {
bitnum = 0;
++byte;
}
}
return result;
}
void bitstream_unpack(struct bitstream * stream,
unsigned int * result,
size_t count,
size_t bitsize)
{
assert(bitstream_remaining(stream) >= (count * bitsize));
while (count--)
*(result++) = bitstream_read(stream, bitsize);
}
int bitstream_write(struct bitstream * stream,
unsigned int value,
size_t bits)
{
unsigned char * byte;
size_t bitnum;
if (ensure_available(stream, bits) != 0)
return -1;
byte = stream->buffer + (stream->pos / CHAR_BIT);
bitnum = stream->pos % CHAR_BIT;
stream->pos += bits;
stream->count = stream->pos; /* truncate */
while (bits-- > 0) {
int bit = (value >> bits) & 0x1;
unsigned char mask = 1 << bitnum++;
*byte = (*byte & ~mask) | (bit ? mask : 0);
if (bitnum == CHAR_BIT) {
bitnum = 0;
++byte;
}
}
return 0;
}
int bitstream_pack(struct bitstream * stream,
const unsigned int * values,
size_t count,
size_t bitsize)
{
if (ensure_available(stream, count * bitsize) != 0)
return -1;
while (count--)
bitstream_write(stream, *(values++), bitsize);
return 0;
}
int bitstream_cat(struct bitstream * dest, const struct bitstream * src)
{
size_t count = bitstream_size(src);
size_t srcpos;
if (ensure_available(dest, count) != 0)
return -1;
srcpos = bitstream_tell(src);
bitstream_seek((struct bitstream *)src, 0);
/* uint must be at least 16 bits */
for (; count >= 16; count -= 16)
bitstream_write(
dest,
bitstream_read((struct bitstream *)src, 16),
16);
if (count > 0)
bitstream_write(
dest,
bitstream_read((struct bitstream *)src, count),
count);
bitstream_seek((struct bitstream *)src, srcpos);
return 0;
}
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