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/*
* FILE: bitstream.c
* PROGRAM: RAT
* AUTHOR: Orion Hodson
*
* Copyright (c) 1998-2001 University College London
* All rights reserved.
*/
#ifndef HIDE_SOURCE_STRINGS
static const char cvsid[] =
"$Id: bitstream.c,v 1.8 2001/01/08 20:29:52 ucaccsp Exp $";
#endif /* HIDE_SOURCE_STRINGS */
#include "config_unix.h"
#include "config_win32.h"
#include "memory.h"
#include "bitstream.h"
typedef struct s_bitstream {
u_char *buf; /* head of bitstream */
u_char *pos; /* current byte in bitstream */
unsigned int remain; /* bits remaining */
unsigned int len; /* length of bitstream in bytes */
} bs;
int
bs_create(bitstream_t **ppb)
{
bs *pb;
pb = (bs*)xmalloc(sizeof(bs));
if (pb) {
memset(pb, 0, sizeof(bs));
*ppb = pb;
return TRUE;
}
return FALSE;
}
int
bs_destroy(bitstream_t **ppb)
{
xfree(*ppb);
return TRUE;
}
int
bs_attach(bitstream_t *b,
u_char *buf,
int blen)
{
b->buf = b->pos = buf;
b->remain = 8;
b->len = blen;
return TRUE;
}
int
bs_put(bitstream_t *b,
u_char bits,
uint8_t nbits)
{
assert(nbits != 0 && nbits <= 8);
if (b->remain == 0) {
b->pos++;
b->remain = 8;
}
if (nbits > b->remain) {
unsigned int over = nbits - b->remain;
(*b->pos) |= (bits >> over);
b->pos++;
b->remain = 8 - over;
(*b->pos) = (bits << b->remain);
} else {
(*b->pos) |= bits << (b->remain - nbits);
b->remain -= nbits;
}
assert((unsigned int)(b->pos - b->buf) <= b->len);
return TRUE;
}
u_char
bs_get(bitstream_t *b,
uint8_t nbits)
{
u_char out;
if (b->remain == 0) {
b->pos++;
b->remain = 8;
}
if (nbits > b->remain) {
/* Get high bits */
out = *b->pos;
out <<= (8 - b->remain);
out >>= (8 - nbits);
b->pos++;
b->remain += 8 - nbits;
out |= (*b->pos) >> b->remain;
} else {
out = *b->pos;
out <<= (8 - b->remain);
out >>= (8 - nbits);
b->remain -= nbits;
}
assert((unsigned int)(b->pos - b->buf) <= b->len);
return out;
}
int
bs_bytes_used(bitstream_t *b)
{
unsigned int used = (unsigned int)(b->pos - b->buf);
if (b->remain != 8) {
used++;
}
return used;
}
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