FFmpeg/libavcodec/cabac.c

/*
 * H.26L/H.264/AVC/JVT/14496-10/... encoder/decoder
 * Copyright (c) 2003 Michael Niedermayer <michaelni@gmx.at>
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * FFmpeg is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

/**
 * @file
 * Context Adaptive Binary Arithmetic Coder.
 */

#include "libavutil/error.h"
#include "libavutil/mem_internal.h"

#include "cabac.h"

DECLARE_ASM_ALIGNED(1, const uint8_t, ff_h264_cabac_tables)[512 + 4*2*64 + 4*64 + 63] = {
    9,8,7,7,6,6,6,6,5,5,5,5,5,5,5,5,
    4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,
    3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,
    3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,
    2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
    2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
    2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
    2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
    1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
    1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
    1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
    1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    // LPS range
    -128,    -128,    -128,    -128,    -128,    -128,    123,     123,
    116,     116,     111,     111,     105,     105,     100,     100,
    95,      95,      90,      90,      85,      85,      81,      81,
    77,      77,      73,      73,      69,      69,      66,      66,
    62,      62,      59,      59,      56,      56,      53,      53,
    51,      51,      48,      48,      46,      46,      43,      43,
    41,      41,      39,      39,      37,      37,      35,      35,
    33,      33,      32,      32,      30,      30,      29,      29,
    27,      27,      26,      26,      24,      24,      23,      23,
    22,      22,      21,      21,      20,      20,      19,      19,
    18,      18,      17,      17,      16,      16,      15,      15,
    14,      14,      14,      14,      13,      13,      12,      12,
    12,      12,      11,      11,      11,      11,      10,      10,
    10,      10,      9,       9,       9,       9,       8,       8,
    8,       8,       7,       7,       7,       7,       7,       7,
    6,       6,       6,       6,       6,       6,       2,       2,
    -80,     -80,     -89,     -89,     -98,     -98,     -106,    -106,
    -114,    -114,    -121,    -121,    -128,    -128,    122,     122,
    116,     116,     110,     110,     104,     104,     99,      99,
    94,      94,      89,      89,      85,      85,      80,      80,
    76,      76,      72,      72,      69,      69,      65,      65,
    62,      62,      59,      59,      56,      56,      53,      53,
    50,      50,      48,      48,      45,      45,      43,      43,
    41,      41,      39,      39,      37,      37,      35,      35,
    33,      33,      31,      31,      30,      30,      28,      28,
    27,      27,      26,      26,      24,      24,      23,      23,
    22,      22,      21,      21,      20,      20,      19,      19,
    18,      18,      17,      17,      16,      16,      15,      15,
    14,      14,      14,      14,      13,      13,      12,      12,
    12,      12,      11,      11,      11,      11,      10,      10,
    9,       9,       9,       9,       9,       9,       8,       8,
    8,       8,       7,       7,       7,       7,       2,       2,
    -48,     -48,     -59,     -59,     -69,     -69,     -78,     -78,
    -87,     -87,     -96,     -96,     -104,    -104,    -112,    -112,
    -119,    -119,    -126,    -126,    123,     123,     117,     117,
    111,     111,     105,     105,     100,     100,     95,      95,
    90,      90,      86,      86,      81,      81,      77,      77,
    73,      73,      69,      69,      66,      66,      63,      63,
    59,      59,      56,      56,      54,      54,      51,      51,
    48,      48,      46,      46,      43,      43,      41,      41,
    39,      39,      37,      37,      35,      35,      33,      33,
    32,      32,      30,      30,      29,      29,      27,      27,
    26,      26,      25,      25,      23,      23,      22,      22,
    21,      21,      20,      20,      19,      19,      18,      18,
    17,      17,      16,      16,      15,      15,      15,      15,
    14,      14,      13,      13,      12,      12,      12,      12,
    11,      11,      11,      11,      10,      10,      10,      10,
    9,       9,       9,       9,       8,       8,       2,       2,
    -16,     -16,     -29,     -29,     -40,     -40,     -51,     -51,
    -61,     -61,     -71,     -71,     -81,     -81,     -90,     -90,
    -98,     -98,     -106,    -106,    -114,    -114,    -121,    -121,
    -128,    -128,    122,     122,     116,     116,     110,     110,
    104,     104,     99,      99,      94,      94,      89,      89,
    85,      85,      80,      80,      76,      76,      72,      72,
    69,      69,      65,      65,      62,      62,      59,      59,
    56,      56,      53,      53,      50,      50,      48,      48,
    45,      45,      43,      43,      41,      41,      39,      39,
    37,      37,      35,      35,      33,      33,      31,      31,
    30,      30,      28,      28,      27,      27,      25,      25,
    24,      24,      23,      23,      22,      22,      21,      21,
    20,      20,      19,      19,      18,      18,      17,      17,
    16,      16,      15,      15,      14,      14,      14,      14,
    13,      13,      12,      12,      12,      12,      11,      11,
    11,      11,      10,      10,      9,       9,       2,       2,
    // mlps state
    127,     126,     77,      76,      77,      76,      75,      74,
    75,      74,      75,      74,      73,      72,      73,      72,
    73,      72,      71,      70,      71,      70,      71,      70,
    69,      68,      69,      68,      67,      66,      67,      66,
    67,      66,      65,      64,      65,      64,      63,      62,
    61,      60,      61,      60,      61,      60,      59,      58,
    59,      58,      57,      56,      55,      54,      55,      54,
    53,      52,      53,      52,      51,      50,      49,      48,
    49,      48,      47,      46,      45,      44,      45,      44,
    43,      42,      43,      42,      39,      38,      39,      38,
    37,      36,      37,      36,      33,      32,      33,      32,
    31,      30,      31,      30,      27,      26,      27,      26,
    25,      24,      23,      22,      23,      22,      19,      18,
    19,      18,      17,      16,      15,      14,      13,      12,
    11,      10,      9,       8,       9,       8,       5,       4,
    5,       4,       3,       2,       1,       0,       0,       1,
    2,       3,       4,       5,       6,       7,       8,       9,
    10,      11,      12,      13,      14,      15,      16,      17,
    18,      19,      20,      21,      22,      23,      24,      25,
    26,      27,      28,      29,      30,      31,      32,      33,
    34,      35,      36,      37,      38,      39,      40,      41,
    42,      43,      44,      45,      46,      47,      48,      49,
    50,      51,      52,      53,      54,      55,      56,      57,
    58,      59,      60,      61,      62,      63,      64,      65,
    66,      67,      68,      69,      70,      71,      72,      73,
    74,      75,      76,      77,      78,      79,      80,      81,
    82,      83,      84,      85,      86,      87,      88,      89,
    90,      91,      92,      93,      94,      95,      96,      97,
    98,      99,      100,     101,     102,     103,     104,     105,
    106,     107,     108,     109,     110,     111,     112,     113,
    114,     115,     116,     117,     118,     119,     120,     121,
    122,     123,     124,     125,     124,     125,     126,     127,
    // last_coeff_flag_offset_8x8
    0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
    3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4,
    5, 5, 5, 5, 6, 6, 6, 6, 7, 7, 7, 7, 8, 8, 8
};

/**
 *
 * @param buf_size size of buf in bits
 */
int ff_init_cabac_decoder(CABACContext *c, const uint8_t *buf, int buf_size){
    c->bytestream_start=
    c->bytestream= buf;
    c->bytestream_end= buf + buf_size;

#if CABAC_BITS == 16
    c->low =  (*c->bytestream++)<<18;
    c->low+=  (*c->bytestream++)<<10;
    // Keep our fetches on a 2-byte boundary as this should avoid ever having to
    // do unaligned loads if the compiler (or asm) optimises the double byte
    // load into a single instruction
    if(((uintptr_t)c->bytestream & 1) == 0) {
        c->low += (1 << 9);
    }
    else {
        c->low += ((*c->bytestream++) << 2) + 2;
    }
#else
    c->low =  (*c->bytestream++)<<10;
    c->low+= ((*c->bytestream++)<<2) + 2;
#endif
    c->range= 0x1FE;
    if ((c->range<<(CABAC_BITS+1)) < c->low)
        return AVERROR_INVALIDDATA;
    return 0;
}