bistream.c

/*
 * FILE:    bitstream.c
 * PROGRAM: RAT
 * AUTHOR:  Orion Hodson
 *
 * Copyright (c) 1998-2001 University College London
 * All rights reserved.
 */

#ifdef WIN32
    #include <malloc.h>
#else
    #include <stdlib.h>
#endif

#include <stdint.h>
#include <stdio.h>
#include <stdbool.h>
#include <assert.h>

#include "bitstream.h"

#define FALSE 0
#define TRUE 1
typedef int BOOL;

typedef struct s_bitstream {
        uint8_t *buf;    /* head of bitstream            */
        uint8_t *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*)calloc(1, sizeof(bs));
        if (pb) {
            *ppb = pb;
            return TRUE;
        }
        return FALSE;
}

int bs_destroy(bitstream_t **ppb)
{
        free(*ppb);
        return TRUE;
}

int bs_attach(bitstream_t *b,
          uint8_t *buf,
          int blen)
{
        b->buf    = b->pos = buf;
        b->remain = 8;
        b->len    = blen;
        return TRUE;
}

int bs_put(bitstream_t *b,
       uint8_t       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;
}

uint8_t bs_get(bitstream_t *b,
       uint8_t  nbits)
{
        uint8_t 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;
}