Function ff_bgmc_decode

libavcodec/bgmc.c:512–566

Reads and decodes a block Gilbert-Moore coded symbol */

/** Reads and decodes a block Gilbert-Moore coded symbol
 */
void ff_bgmc_decode(GetBitContext *gb, unsigned int num, int32_t *dst,
                 unsigned int delta, unsigned int sx,
                 unsigned int *h, unsigned int *l, unsigned int *v,
                 uint8_t *cf_lut, unsigned int *cf_lut_status)
{
    unsigned int i;
    uint8_t *lut = bgmc_lut_getp(cf_lut, cf_lut_status, delta);

    // read current state
    unsigned int high   = *h;
    unsigned int low    = *l;
    unsigned int value  = *v;

    lut += sx * LUT_SIZE;

    // decode num samples
    for (i = 0; i < num; i++) {
        unsigned int range  = high - low + 1;
        unsigned int target = (((value - low + 1) << FREQ_BITS) - 1) / range;
        unsigned int symbol = lut[target >> (FREQ_BITS - LUT_BITS)] << delta;

        while (cf_table[sx][symbol] > target)
            symbol += 1 << delta;

        symbol = (symbol >> delta) - 1;

        high = low + ((range * cf_table[sx][(symbol    ) << delta] - (1 << FREQ_BITS)) >> FREQ_BITS);
        low  = low + ((range * cf_table[sx][(symbol + 1) << delta]                   ) >> FREQ_BITS);

        while (1) {
            if (high >= HALF) {
                if        (low >= HALF) {
                    value -= HALF;
                    low   -= HALF;
                    high  -= HALF;
                } else if (low >= FIRST_QTR && high < THIRD_QTR) {
                    value -= FIRST_QTR;
                    low   -= FIRST_QTR;
                    high  -= FIRST_QTR;
                } else break;
            }

            low   *= 2;
            high   = 2 * high  + 1;
            value  = 2 * value + get_bits1(gb);
        }

        *dst++ = symbol;
    }

    // save current state
    *h = high;
    *l = low;
    *v = value;
}