208 lines
6.8 KiB
C
208 lines
6.8 KiB
C
/*
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* Copyright © 2018, VideoLAN and dav1d authors
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* Copyright © 2018, Two Orioles, LLC
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* 1. Redistributions of source code must retain the above copyright notice, this
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* list of conditions and the following disclaimer.
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*
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* 2. Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
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* ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#include "config.h"
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#include <limits.h>
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#include "common/intops.h"
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#include "src/msac.h"
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#define EC_PROB_SHIFT 6
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#define EC_MIN_PROB 4 // must be <= (1<<EC_PROB_SHIFT)/16
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#define EC_WIN_SIZE (sizeof(ec_win) << 3)
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static inline void ctx_refill(MsacContext *const s) {
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const uint8_t *buf_pos = s->buf_pos;
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const uint8_t *buf_end = s->buf_end;
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int c = EC_WIN_SIZE - s->cnt - 24;
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ec_win dif = s->dif;
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while (c >= 0 && buf_pos < buf_end) {
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dif ^= ((ec_win)*buf_pos++) << c;
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c -= 8;
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}
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s->dif = dif;
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s->cnt = EC_WIN_SIZE - c - 24;
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s->buf_pos = buf_pos;
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}
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/* Takes updated dif and range values, renormalizes them so that
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* 32768 <= rng < 65536 (reading more bytes from the stream into dif if
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* necessary), and stores them back in the decoder context.
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* dif: The new value of dif.
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* rng: The new value of the range. */
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static inline void ctx_norm(MsacContext *const s, const ec_win dif,
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const unsigned rng)
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{
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const int d = 15 ^ (31 ^ clz(rng));
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assert(rng <= 65535U);
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s->cnt -= d;
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s->dif = ((dif + 1) << d) - 1; /* Shift in 1s in the LSBs */
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s->rng = rng << d;
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if (s->cnt < 0)
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ctx_refill(s);
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}
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unsigned dav1d_msac_decode_bool_equi_c(MsacContext *const s) {
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const unsigned r = s->rng;
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ec_win dif = s->dif;
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assert((dif >> (EC_WIN_SIZE - 16)) < r);
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// When the probability is 1/2, f = 16384 >> EC_PROB_SHIFT = 256 and we can
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// replace the multiply with a simple shift.
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unsigned v = ((r >> 8) << 7) + EC_MIN_PROB;
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const ec_win vw = (ec_win)v << (EC_WIN_SIZE - 16);
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const unsigned ret = dif >= vw;
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dif -= ret * vw;
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v += ret * (r - 2 * v);
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ctx_norm(s, dif, v);
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return !ret;
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}
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/* Decode a single binary value.
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* f: The probability that the bit is one
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* Return: The value decoded (0 or 1). */
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unsigned dav1d_msac_decode_bool_c(MsacContext *const s, const unsigned f) {
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const unsigned r = s->rng;
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ec_win dif = s->dif;
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assert((dif >> (EC_WIN_SIZE - 16)) < r);
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unsigned v = ((r >> 8) * (f >> EC_PROB_SHIFT) >> (7 - EC_PROB_SHIFT)) + EC_MIN_PROB;
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const ec_win vw = (ec_win)v << (EC_WIN_SIZE - 16);
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const unsigned ret = dif >= vw;
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dif -= ret * vw;
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v += ret * (r - 2 * v);
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ctx_norm(s, dif, v);
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return !ret;
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}
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int dav1d_msac_decode_subexp(MsacContext *const s, const int ref,
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const int n, unsigned k)
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{
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assert(n >> k == 8);
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unsigned a = 0;
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if (dav1d_msac_decode_bool_equi(s)) {
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if (dav1d_msac_decode_bool_equi(s))
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k += dav1d_msac_decode_bool_equi(s) + 1;
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a = 1 << k;
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}
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const unsigned v = dav1d_msac_decode_bools(s, k) + a;
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return ref * 2 <= n ? inv_recenter(ref, v) :
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n - 1 - inv_recenter(n - 1 - ref, v);
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}
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/* Decodes a symbol given an inverse cumulative distribution function (CDF)
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* table in Q15. */
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unsigned dav1d_msac_decode_symbol_adapt_c(MsacContext *const s,
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uint16_t *const cdf,
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const size_t n_symbols)
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{
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const unsigned c = s->dif >> (EC_WIN_SIZE - 16), r = s->rng >> 8;
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unsigned u, v = s->rng, val = -1;
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assert(n_symbols <= 15);
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assert(cdf[n_symbols] <= 32);
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do {
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val++;
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u = v;
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v = r * (cdf[val] >> EC_PROB_SHIFT);
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v >>= 7 - EC_PROB_SHIFT;
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v += EC_MIN_PROB * ((unsigned)n_symbols - val);
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} while (c < v);
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assert(u <= s->rng);
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ctx_norm(s, s->dif - ((ec_win)v << (EC_WIN_SIZE - 16)), u - v);
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if (s->allow_update_cdf) {
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const unsigned count = cdf[n_symbols];
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const unsigned rate = 4 + (count >> 4) + (n_symbols > 2);
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unsigned i;
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for (i = 0; i < val; i++)
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cdf[i] += (32768 - cdf[i]) >> rate;
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for (; i < n_symbols; i++)
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cdf[i] -= cdf[i] >> rate;
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cdf[n_symbols] = count + (count < 32);
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}
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return val;
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}
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unsigned dav1d_msac_decode_bool_adapt_c(MsacContext *const s,
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uint16_t *const cdf)
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{
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const unsigned bit = dav1d_msac_decode_bool(s, *cdf);
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if (s->allow_update_cdf) {
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// update_cdf() specialized for boolean CDFs
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const unsigned count = cdf[1];
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const int rate = 4 + (count >> 4);
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if (bit)
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cdf[0] += (32768 - cdf[0]) >> rate;
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else
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cdf[0] -= cdf[0] >> rate;
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cdf[1] = count + (count < 32);
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}
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return bit;
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}
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unsigned dav1d_msac_decode_hi_tok_c(MsacContext *const s, uint16_t *const cdf) {
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unsigned tok_br = dav1d_msac_decode_symbol_adapt4(s, cdf, 3);
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unsigned tok = 3 + tok_br;
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if (tok_br == 3) {
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tok_br = dav1d_msac_decode_symbol_adapt4(s, cdf, 3);
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tok = 6 + tok_br;
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if (tok_br == 3) {
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tok_br = dav1d_msac_decode_symbol_adapt4(s, cdf, 3);
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tok = 9 + tok_br;
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if (tok_br == 3)
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tok = 12 + dav1d_msac_decode_symbol_adapt4(s, cdf, 3);
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}
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}
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return tok;
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}
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void dav1d_msac_init(MsacContext *const s, const uint8_t *const data,
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const size_t sz, const int disable_cdf_update_flag)
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{
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s->buf_pos = data;
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s->buf_end = data + sz;
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s->dif = ((ec_win)1 << (EC_WIN_SIZE - 1)) - 1;
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s->rng = 0x8000;
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s->cnt = -15;
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s->allow_update_cdf = !disable_cdf_update_flag;
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ctx_refill(s);
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#if ARCH_X86_64 && HAVE_ASM
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s->symbol_adapt16 = dav1d_msac_decode_symbol_adapt_c;
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msac_init_x86(s);
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#endif
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}
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