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  1. /*
  2.  * Copyright (C) 2007 Marco Gerards <marco@gnu.org>
  3.  * Copyright (C) 2009 David Conrad
  4.  *
  5.  * This file is part of FFmpeg.
  6.  *
  7.  * FFmpeg is free software; you can redistribute it and/or
  8.  * modify it under the terms of the GNU Lesser General Public
  9.  * License as published by the Free Software Foundation; either
  10.  * version 2.1 of the License, or (at your option) any later version.
  11.  *
  12.  * FFmpeg is distributed in the hope that it will be useful,
  13.  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14.  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15.  * Lesser General Public License for more details.
  16.  *
  17.  * You should have received a copy of the GNU Lesser General Public
  18.  * License along with FFmpeg; if not, write to the Free Software
  19.  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  20.  */
  21.  
  22. /**
  23.  * @file
  24.  * Arithmetic decoder for Dirac
  25.  * @author Marco Gerards <marco@gnu.org>
  26.  */
  27.  
  28. #ifndef AVCODEC_DIRAC_ARITH_H
  29. #define AVCODEC_DIRAC_ARITH_H
  30.  
  31. #include "bytestream.h"
  32. #include "get_bits.h"
  33.  
  34. enum dirac_arith_contexts {
  35.     CTX_ZPZN_F1,
  36.     CTX_ZPNN_F1,
  37.     CTX_NPZN_F1,
  38.     CTX_NPNN_F1,
  39.     CTX_ZP_F2,
  40.     CTX_ZP_F3,
  41.     CTX_ZP_F4,
  42.     CTX_ZP_F5,
  43.     CTX_ZP_F6,
  44.     CTX_NP_F2,
  45.     CTX_NP_F3,
  46.     CTX_NP_F4,
  47.     CTX_NP_F5,
  48.     CTX_NP_F6,
  49.     CTX_COEFF_DATA,
  50.     CTX_SIGN_NEG,
  51.     CTX_SIGN_ZERO,
  52.     CTX_SIGN_POS,
  53.     CTX_ZERO_BLOCK,
  54.     CTX_DELTA_Q_F,
  55.     CTX_DELTA_Q_DATA,
  56.     CTX_DELTA_Q_SIGN,
  57.  
  58.     DIRAC_CTX_COUNT
  59. };
  60.  
  61. // Dirac resets the arith decoder between decoding various types of data,
  62. // so many contexts are never used simultaneously. Thus, we can reduce
  63. // the number of contexts needed by reusing them.
  64. #define CTX_SB_F1        CTX_ZP_F5
  65. #define CTX_SB_DATA      0
  66. #define CTX_PMODE_REF1   0
  67. #define CTX_PMODE_REF2   1
  68. #define CTX_GLOBAL_BLOCK 2
  69. #define CTX_MV_F1        CTX_ZP_F2
  70. #define CTX_MV_DATA      0
  71. #define CTX_DC_F1        CTX_ZP_F5
  72. #define CTX_DC_DATA      0
  73.  
  74. typedef struct {
  75.     unsigned low;
  76.     uint16_t range;
  77.     int16_t  counter;
  78.  
  79.     const uint8_t *bytestream;
  80.     const uint8_t *bytestream_end;
  81.  
  82.     uint16_t contexts[DIRAC_CTX_COUNT];
  83. } DiracArith;
  84.  
  85. extern const uint8_t ff_dirac_next_ctx[DIRAC_CTX_COUNT];
  86. extern const uint16_t ff_dirac_prob[256];
  87. extern int16_t ff_dirac_prob_branchless[256][2];
  88.  
  89. static inline void renorm(DiracArith *c)
  90. {
  91. #if HAVE_FAST_CLZ
  92.     int shift = 14 - av_log2_16bit(c->range-1) + ((c->range-1)>>15);
  93.  
  94.     c->low    <<= shift;
  95.     c->range  <<= shift;
  96.     c->counter += shift;
  97. #else
  98.     while (c->range <= 0x4000) {
  99.         c->low   <<= 1;
  100.         c->range <<= 1;
  101.         c->counter++;
  102.     }
  103. #endif
  104. }
  105.  
  106. static inline void refill(DiracArith *c)
  107. {
  108.     int counter = c->counter;
  109.  
  110.     if (counter >= 0) {
  111.         int new = bytestream_get_be16(&c->bytestream);
  112.  
  113.         // the spec defines overread bits to be 1, and streams rely on this
  114.         if (c->bytestream > c->bytestream_end) {
  115.             new |= 0xff;
  116.             if (c->bytestream > c->bytestream_end+1)
  117.                 new |= 0xff00;
  118.  
  119.             c->bytestream = c->bytestream_end;
  120.         }
  121.  
  122.         c->low += new << counter;
  123.         counter -= 16;
  124.     }
  125.     c->counter = counter;
  126. }
  127.  
  128. static inline int dirac_get_arith_bit(DiracArith *c, int ctx)
  129. {
  130.     int prob_zero = c->contexts[ctx];
  131.     int range_times_prob, bit;
  132.     unsigned low = c->low;
  133.     int    range = c->range;
  134.  
  135.     range_times_prob = (c->range * prob_zero) >> 16;
  136.  
  137. #if HAVE_FAST_CMOV && HAVE_INLINE_ASM
  138.     low   -= range_times_prob << 16;
  139.     range -= range_times_prob;
  140.     bit = 0;
  141.     __asm__(
  142.         "cmpl   %5, %4 \n\t"
  143.         "setae  %b0    \n\t"
  144.         "cmovb  %3, %2 \n\t"
  145.         "cmovb  %5, %1 \n\t"
  146.         : "+q"(bit), "+r"(range), "+r"(low)
  147.         : "r"(c->low), "r"(c->low>>16),
  148.           "r"(range_times_prob)
  149.     );
  150. #else
  151.     bit = (low >> 16) >= range_times_prob;
  152.     if (bit) {
  153.         low   -= range_times_prob << 16;
  154.         range -= range_times_prob;
  155.     } else {
  156.         range  = range_times_prob;
  157.     }
  158. #endif
  159.  
  160.     c->contexts[ctx] += ff_dirac_prob_branchless[prob_zero>>8][bit];
  161.     c->low   = low;
  162.     c->range = range;
  163.  
  164.     renorm(c);
  165.     refill(c);
  166.     return bit;
  167. }
  168.  
  169. static inline int dirac_get_arith_uint(DiracArith *c, int follow_ctx, int data_ctx)
  170. {
  171.     int ret = 1;
  172.     while (!dirac_get_arith_bit(c, follow_ctx)) {
  173.         ret <<= 1;
  174.         ret += dirac_get_arith_bit(c, data_ctx);
  175.         follow_ctx = ff_dirac_next_ctx[follow_ctx];
  176.     }
  177.     return ret-1;
  178. }
  179.  
  180. static inline int dirac_get_arith_int(DiracArith *c, int follow_ctx, int data_ctx)
  181. {
  182.     int ret = dirac_get_arith_uint(c, follow_ctx, data_ctx);
  183.     if (ret && dirac_get_arith_bit(c, data_ctx+1))
  184.         ret = -ret;
  185.     return ret;
  186. }
  187.  
  188. void ff_dirac_init_arith_decoder(DiracArith *c, GetBitContext *gb, int length);
  189.  
  190. #endif /* AVCODEC_DIRAC_ARITH_H */
  191.