ffmpeg/libavcodec/cabac_functions.h

   1 /*
   2  * H.26L/H.264/AVC/JVT/14496-10/... encoder/decoder
   3  * Copyright (c) 2003 Michael Niedermayer <michaelni@gmx.at>
   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  * Context Adaptive Binary Arithmetic Coder inline functions
  25  */
  26
  27 #ifndef AVCODEC_CABAC_FUNCTIONS_H
  28 #define AVCODEC_CABAC_FUNCTIONS_H
  29
  30 #include <stdint.h>
  31
  32 #include "cabac.h"
  33 #include "config.h"
  34
  35 #ifndef UNCHECKED_BITSTREAM_READER
  36 #define UNCHECKED_BITSTREAM_READER !CONFIG_SAFE_BITSTREAM_READER
  37 #endif
  38
  39 #if ARCH_AARCH64
  40 #   include "aarch64/cabac.h"
  41 #endif
  42 #if ARCH_ARM
  43 #   include "arm/cabac.h"
  44 #endif
  45 #if ARCH_X86
  46 #   include "x86/cabac.h"
  47 #endif
  48
  49 static CABAC_TABLE_CONST uint8_t * const ff_h264_norm_shift = ff_h264_cabac_tables + H264_NORM_SHIFT_OFFSET;
  50 static CABAC_TABLE_CONST uint8_t * const ff_h264_lps_range = ff_h264_cabac_tables + H264_LPS_RANGE_OFFSET;
  51 static CABAC_TABLE_CONST uint8_t * const ff_h264_mlps_state = ff_h264_cabac_tables + H264_MLPS_STATE_OFFSET;
  52 static CABAC_TABLE_CONST uint8_t * const ff_h264_last_coeff_flag_offset_8x8 = ff_h264_cabac_tables + H264_LAST_COEFF_FLAG_OFFSET_8x8_OFFSET;
  53
  54 static void refill(CABACContext *c){
  55 #if CABAC_BITS == 16
  56         c->low+= (c->bytestream[0]<<9) + (c->bytestream[1]<<1);
  57 #else
  58         c->low+= c->bytestream[0]<<1;
  59 #endif
  60     c->low -= CABAC_MASK;
  61 #if !UNCHECKED_BITSTREAM_READER
  62     if (c->bytestream < c->bytestream_end)
  63 #endif
  64         c->bytestream += CABAC_BITS / 8;
  65 }
  66
  67 static inline void renorm_cabac_decoder_once(CABACContext *c){
  68     int shift= (uint32_t)(c->range - 0x100)>>31;
  69     c->range<<= shift;
  70     c->low  <<= shift;
  71     if(!(c->low & CABAC_MASK))
  72         refill(c);
  73 }
  74
  75 #ifndef get_cabac_inline
  76 static void refill2(CABACContext *c){
  77     int i, x;
  78
  79     x= c->low ^ (c->low-1);
  80     i= 7 - ff_h264_norm_shift[x>>(CABAC_BITS-1)];
  81
  82     x= -CABAC_MASK;
  83
  84 #if CABAC_BITS == 16
  85         x+= (c->bytestream[0]<<9) + (c->bytestream[1]<<1);
  86 #else
  87         x+= c->bytestream[0]<<1;
  88 #endif
  89
  90     c->low += x<<i;
  91 #if !UNCHECKED_BITSTREAM_READER
  92     if (c->bytestream < c->bytestream_end)
  93 #endif
  94         c->bytestream += CABAC_BITS/8;
  95 }
  96
  97 static av_always_inline int get_cabac_inline(CABACContext *c, uint8_t * const state){
  98     int s = *state;
  99     int RangeLPS= ff_h264_lps_range[2*(c->range&0xC0) + s];
 100     int bit, lps_mask;
 101
 102     c->range -= RangeLPS;
 103     lps_mask= ((c->range<<(CABAC_BITS+1)) - c->low)>>31;
 104
 105     c->low -= (c->range<<(CABAC_BITS+1)) & lps_mask;
 106     c->range += (RangeLPS - c->range) & lps_mask;
 107
 108     s^=lps_mask;
 109     *state= (ff_h264_mlps_state+128)[s];
 110     bit= s&1;
 111
 112     lps_mask= ff_h264_norm_shift[c->range];
 113     c->range<<= lps_mask;
 114     c->low  <<= lps_mask;
 115     if(!(c->low & CABAC_MASK))
 116         refill2(c);
 117     return bit;
 118 }
 119 #endif
 120
 121 static int av_noinline av_unused get_cabac_noinline(CABACContext *c, uint8_t * const state){
 122     return get_cabac_inline(c,state);
 123 }
 124
 125 static int av_unused get_cabac(CABACContext *c, uint8_t * const state){
 126     return get_cabac_inline(c,state);
 127 }
 128
 129 #ifndef get_cabac_bypass
 130 static int av_unused get_cabac_bypass(CABACContext *c){
 131     int range;
 132     c->low += c->low;
 133
 134     if(!(c->low & CABAC_MASK))
 135         refill(c);
 136
 137     range= c->range<<(CABAC_BITS+1);
 138     if(c->low < range){
 139         return 0;
 140     }else{
 141         c->low -= range;
 142         return 1;
 143     }
 144 }
 145 #endif
 146
 147 #ifndef get_cabac_bypass_sign
 148 static av_always_inline int get_cabac_bypass_sign(CABACContext *c, int val){
 149     int range, mask;
 150     c->low += c->low;
 151
 152     if(!(c->low & CABAC_MASK))
 153         refill(c);
 154
 155     range= c->range<<(CABAC_BITS+1);
 156     c->low -= range;
 157     mask= c->low >> 31;
 158     range &= mask;
 159     c->low += range;
 160     return (val^mask)-mask;
 161 }
 162 #endif
 163
 164 /**
 165  *
 166  * @return the number of bytes read or 0 if no end
 167  */
 168 static int av_unused get_cabac_terminate(CABACContext *c){
 169     c->range -= 2;
 170     if(c->low < c->range<<(CABAC_BITS+1)){
 171         renorm_cabac_decoder_once(c);
 172         return 0;
 173     }else{
 174         return c->bytestream - c->bytestream_start;
 175     }
 176 }
 177
 178 /**
 179  * Skip @p n bytes and reset the decoder.
 180  * @return the address of the first skipped byte or NULL if there's less than @p n bytes left
 181  */
 182 static av_unused const uint8_t* skip_bytes(CABACContext *c, int n) {
 183     const uint8_t *ptr = c->bytestream;
 184
 185     if (c->low & 0x1)
 186         ptr--;
 187 #if CABAC_BITS == 16
 188     if (c->low & 0x1FF)
 189         ptr--;
 190 #endif
 191     if ((int) (c->bytestream_end - ptr) < n)
 192         return NULL;
 193     ff_init_cabac_decoder(c, ptr + n, c->bytestream_end - ptr - n);
 194
 195     return ptr;
 196 }
 197
 198 #endif /* AVCODEC_CABAC_FUNCTIONS_H */