/* * Copyright © 2018, VideoLAN and dav1d authors * Copyright © 2018, Two Orioles, LLC * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions are met: * * 1. Redistributions of source code must retain the above copyright notice, this *    list of conditions and the following disclaimer. * * 2. Redistributions in binary form must reproduce the above copyright notice, *    this list of conditions and the following disclaimer in the documentation *    and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ #include "config.h" #include <limits.h> #include "common/intops.h" #include "src/msac.h" #define EC_PROB_SHIFT 6#define EC_MIN_PROB 4  // must be <= (1<<EC_PROB_SHIFT)/16 #define EC_WIN_SIZE (sizeof(ec_win) << 3) static inline void ctx_refill(MsacContext *const s) {    const uint8_t *buf_pos = s->buf_pos;    const uint8_t *buf_end = s->buf_end;    int c = EC_WIN_SIZE - s->cnt - 24;    ec_win dif = s->dif;    while (c >= 0 && buf_pos < buf_end) {        dif ^= ((ec_win)*buf_pos++) << c;        c -= 8;    }    s->dif = dif;    s->cnt = EC_WIN_SIZE - c - 24;    s->buf_pos = buf_pos;} /* Takes updated dif and range values, renormalizes them so that * 32768 <= rng < 65536 (reading more bytes from the stream into dif if * necessary), and stores them back in the decoder context. * dif: The new value of dif. * rng: The new value of the range. */static inline void ctx_norm(MsacContext *const s, const ec_win dif,                            const unsigned rng){    const int d = 15 ^ (31 ^ clz(rng));    assert(rng <= 65535U);    s->cnt -= d;    s->dif = ((dif + 1) << d) - 1; /* Shift in 1s in the LSBs */    s->rng = rng << d;    if (s->cnt < 0)        ctx_refill(s);} unsigned dav1d_msac_decode_bool_equi_c(MsacContext *const s) {    const unsigned r = s->rng;    ec_win dif = s->dif;    assert((dif >> (EC_WIN_SIZE - 16)) < r);    // When the probability is 1/2, f = 16384 >> EC_PROB_SHIFT = 256 and we can    // replace the multiply with a simple shift.    unsigned v = ((r >> 8) << 7) + EC_MIN_PROB;    const ec_win vw = (ec_win)v << (EC_WIN_SIZE - 16);    const unsigned ret = dif >= vw;    dif -= ret * vw;    v += ret * (r - 2 * v);    ctx_norm(s, dif, v);    return !ret;} /* Decode a single binary value. * f: The probability that the bit is one * Return: The value decoded (0 or 1). */unsigned dav1d_msac_decode_bool_c(MsacContext *const s, const unsigned f) {    const unsigned r = s->rng;    ec_win dif = s->dif;    assert((dif >> (EC_WIN_SIZE - 16)) < r);    unsigned v = ((r >> 8) * (f >> EC_PROB_SHIFT) >> (7 - EC_PROB_SHIFT)) + EC_MIN_PROB;    const ec_win vw = (ec_win)v << (EC_WIN_SIZE - 16);    const unsigned ret = dif >= vw;    dif -= ret * vw;    v += ret * (r - 2 * v);    ctx_norm(s, dif, v);    return !ret;} int dav1d_msac_decode_subexp(MsacContext *const s, const int ref,                             const int n, unsigned k){    assert(n >> k == 8);     unsigned a = 0;    if (dav1d_msac_decode_bool_equi(s)) {        if (dav1d_msac_decode_bool_equi(s))            k += dav1d_msac_decode_bool_equi(s) + 1;        a = 1 << k;    }    const unsigned v = dav1d_msac_decode_bools(s, k) + a;    return ref * 2 <= n ? inv_recenter(ref, v) :                          n - 1 - inv_recenter(n - 1 - ref, v);} /* Decodes a symbol given an inverse cumulative distribution function (CDF) * table in Q15. */unsigned dav1d_msac_decode_symbol_adapt_c(MsacContext *const s,                                          uint16_t *const cdf,                                          const size_t n_symbols){    const unsigned c = s->dif >> (EC_WIN_SIZE - 16), r = s->rng >> 8;    unsigned u, v = s->rng, val = -1;     assert(n_symbols <= 15);    assert(cdf[n_symbols] <= 32);     do {        val++;        u = v;        v = r * (cdf[val] >> EC_PROB_SHIFT);        v >>= 7 - EC_PROB_SHIFT;        v += EC_MIN_PROB * ((unsigned)n_symbols - val);    } while (c < v);     assert(u <= s->rng);     ctx_norm(s, s->dif - ((ec_win)v << (EC_WIN_SIZE - 16)), u - v);     if (s->allow_update_cdf) {        const unsigned count = cdf[n_symbols];        const unsigned rate = 4 + (count >> 4) + (n_symbols > 2);        unsigned i;        for (i = 0; i < val; i++)            cdf[i] += (32768 - cdf[i]) >> rate;        for (; i < n_symbols; i++)            cdf[i] -= cdf[i] >> rate;        cdf[n_symbols] = count + (count < 32);    }     return val;} unsigned dav1d_msac_decode_bool_adapt_c(MsacContext *const s,                                        uint16_t *const cdf){    const unsigned bit = dav1d_msac_decode_bool(s, *cdf);     if (s->allow_update_cdf) {        // update_cdf() specialized for boolean CDFs        const unsigned count = cdf[1];        const int rate = 4 + (count >> 4);        if (bit)            cdf[0] += (32768 - cdf[0]) >> rate;        else            cdf[0] -= cdf[0] >> rate;        cdf[1] = count + (count < 32);    }     return bit;} unsigned dav1d_msac_decode_hi_tok_c(MsacContext *const s, uint16_t *const cdf) {    unsigned tok_br = dav1d_msac_decode_symbol_adapt4(s, cdf, 3);    unsigned tok = 3 + tok_br;    if (tok_br == 3) {        tok_br = dav1d_msac_decode_symbol_adapt4(s, cdf, 3);        tok = 6 + tok_br;        if (tok_br == 3) {            tok_br = dav1d_msac_decode_symbol_adapt4(s, cdf, 3);            tok = 9 + tok_br;            if (tok_br == 3)                tok = 12 + dav1d_msac_decode_symbol_adapt4(s, cdf, 3);        }    }    return tok;} void dav1d_msac_init(MsacContext *const s, const uint8_t *const data,                     const size_t sz, const int disable_cdf_update_flag){    s->buf_pos = data;    s->buf_end = data + sz;    s->dif = ((ec_win)1 << (EC_WIN_SIZE - 1)) - 1;    s->rng = 0x8000;    s->cnt = -15;    s->allow_update_cdf = !disable_cdf_update_flag;    ctx_refill(s); #if ARCH_X86_64 && HAVE_ASM    s->symbol_adapt16 = dav1d_msac_decode_symbol_adapt_c;     dav1d_msac_init_x86(s);#endif}