media/ffvpx/libavcodec/vpx_rac.h

   1 /*
   2  * Copyright (C) 2006  Aurelien Jacobs <aurel@gnuage.org>
   3  *
   4  * This file is part of FFmpeg.
   5  *
   6  * FFmpeg is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU Lesser General Public
   8  * License as published by the Free Software Foundation; either
   9  * version 2.1 of the License, or (at your option) any later version.
  10  *
  11  * FFmpeg is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14  * Lesser General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU Lesser General Public
  17  * License along with FFmpeg; if not, write to the Free Software
  18  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  19  */
  20
  21 /**
  22  * @file
  23  * Common VP5-VP9 range decoder stuff
  24  */
  25
  26 #ifndef AVCODEC_VPX_RAC_H
  27 #define AVCODEC_VPX_RAC_H
  28
  29 #include <stdint.h>
  30
  31 #include "config.h"
  32 #include "libavutil/attributes.h"
  33 #include "bytestream.h"
  34
  35 typedef struct VPXRangeCoder {
  36     int high;
  37     int bits; /* stored negated (i.e. negative "bits" is a positive number of
  38                  bits left) in order to eliminate a negate in cache refilling */
  39     const uint8_t *buffer;
  40     const uint8_t *end;
  41     unsigned int code_word;
  42     int end_reached;
  43 } VPXRangeCoder;
  44
  45 extern const uint8_t ff_vpx_norm_shift[256];
  46 int ff_vpx_init_range_decoder(VPXRangeCoder *c, const uint8_t *buf, int buf_size);
  47
  48 /**
  49  * returns 1 if the end of the stream has been reached, 0 otherwise.
  50  */
  51 static av_always_inline int vpx_rac_is_end(VPXRangeCoder *c)
  52 {
  53     if (c->end <= c->buffer && c->bits >= 0)
  54         c->end_reached ++;
  55     return c->end_reached > 10;
  56 }
  57
  58 static av_always_inline unsigned int vpx_rac_renorm(VPXRangeCoder *c)
  59 {
  60     int shift = ff_vpx_norm_shift[c->high];
  61     int bits = c->bits;
  62     unsigned int code_word = c->code_word;
  63
  64     c->high   <<= shift;
  65     code_word <<= shift;
  66     bits       += shift;
  67     if(bits >= 0 && c->buffer < c->end) {
  68         code_word |= bytestream_get_be16(&c->buffer) << bits;
  69         bits -= 16;
  70     }
  71     c->bits = bits;
  72     return code_word;
  73 }
  74
  75 #if   ARCH_ARM
  76 #include "arm/vpx_arith.h"
  77 #elif ARCH_X86
  78 #include "x86/vpx_arith.h"
  79 #endif
  80
  81 #ifndef vpx_rac_get_prob
  82 #define vpx_rac_get_prob vpx_rac_get_prob
  83 static av_always_inline int vpx_rac_get_prob(VPXRangeCoder *c, uint8_t prob)
  84 {
  85     unsigned int code_word = vpx_rac_renorm(c);
  86     unsigned int low = 1 + (((c->high - 1) * prob) >> 8);
  87     unsigned int low_shift = low << 16;
  88     int bit = code_word >= low_shift;
  89
  90     c->high = bit ? c->high - low : low;
  91     c->code_word = bit ? code_word - low_shift : code_word;
  92
  93     return bit;
  94 }
  95 #endif
  96
  97 #ifndef vpx_rac_get_prob_branchy
  98 // branchy variant, to be used where there's a branch based on the bit decoded
  99 static av_always_inline int vpx_rac_get_prob_branchy(VPXRangeCoder *c, int prob)
 100 {
 101     unsigned long code_word = vpx_rac_renorm(c);
 102     unsigned low = 1 + (((c->high - 1) * prob) >> 8);
 103     unsigned low_shift = low << 16;
 104
 105     if (code_word >= low_shift) {
 106         c->high     -= low;
 107         c->code_word = code_word - low_shift;
 108         return 1;
 109     }
 110
 111     c->high = low;
 112     c->code_word = code_word;
 113     return 0;
 114 }
 115 #endif
 116
 117 static av_always_inline int vpx_rac_get(VPXRangeCoder *c)
 118 {
 119     unsigned int code_word = vpx_rac_renorm(c);
 120     /* equiprobable */
 121     int low = (c->high + 1) >> 1;
 122     unsigned int low_shift = low << 16;
 123     int bit = code_word >= low_shift;
 124     if (bit) {
 125         c->high   -= low;
 126         code_word -= low_shift;
 127     } else {
 128         c->high = low;
 129     }
 130
 131     c->code_word = code_word;
 132     return bit;
 133 }
 134
 135 #endif /* AVCODEC_VPX_RAC_H */