| 1 | /* |
| 2 | * Range coder |
| 3 | * Copyright (c) 2004 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 | * Range coder. |
| 25 | */ |
| 26 | |
| 27 | #ifndef AVCODEC_RANGECODER_H |
| 28 | #define AVCODEC_RANGECODER_H |
| 29 | |
| 30 | #include <stdint.h> |
| 31 | |
| 32 | #include "libavutil/common.h" |
| 33 | #include "libavutil/avassert.h" |
| 34 | |
| 35 | typedef struct RangeCoder { |
| 36 | int low; |
| 37 | int range; |
| 38 | int outstanding_count; |
| 39 | int outstanding_byte; |
| 40 | uint8_t zero_state[256]; |
| 41 | uint8_t one_state[256]; |
| 42 | uint8_t *bytestream_start; |
| 43 | uint8_t *bytestream; |
| 44 | uint8_t *bytestream_end; |
| 45 | } RangeCoder; |
| 46 | |
| 47 | void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size); |
| 48 | void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, int buf_size); |
| 49 | int ff_rac_terminate(RangeCoder *c); |
| 50 | void ff_build_rac_states(RangeCoder *c, int factor, int max_p); |
| 51 | |
| 52 | static inline void renorm_encoder(RangeCoder *c) |
| 53 | { |
| 54 | // FIXME: optimize |
| 55 | while (c->range < 0x100) { |
| 56 | if (c->outstanding_byte < 0) { |
| 57 | c->outstanding_byte = c->low >> 8; |
| 58 | } else if (c->low <= 0xFF00) { |
| 59 | *c->bytestream++ = c->outstanding_byte; |
| 60 | for (; c->outstanding_count; c->outstanding_count--) |
| 61 | *c->bytestream++ = 0xFF; |
| 62 | c->outstanding_byte = c->low >> 8; |
| 63 | } else if (c->low >= 0x10000) { |
| 64 | *c->bytestream++ = c->outstanding_byte + 1; |
| 65 | for (; c->outstanding_count; c->outstanding_count--) |
| 66 | *c->bytestream++ = 0x00; |
| 67 | c->outstanding_byte = (c->low >> 8) & 0xFF; |
| 68 | } else { |
| 69 | c->outstanding_count++; |
| 70 | } |
| 71 | |
| 72 | c->low = (c->low & 0xFF) << 8; |
| 73 | c->range <<= 8; |
| 74 | } |
| 75 | } |
| 76 | |
| 77 | static inline int get_rac_count(RangeCoder *c) |
| 78 | { |
| 79 | int x = c->bytestream - c->bytestream_start + c->outstanding_count; |
| 80 | if (c->outstanding_byte >= 0) |
| 81 | x++; |
| 82 | return 8 * x - av_log2(c->range); |
| 83 | } |
| 84 | |
| 85 | static inline void put_rac(RangeCoder *c, uint8_t *const state, int bit) |
| 86 | { |
| 87 | int range1 = (c->range * (*state)) >> 8; |
| 88 | |
| 89 | av_assert2(*state); |
| 90 | av_assert2(range1 < c->range); |
| 91 | av_assert2(range1 > 0); |
| 92 | if (!bit) { |
| 93 | c->range -= range1; |
| 94 | *state = c->zero_state[*state]; |
| 95 | } else { |
| 96 | c->low += c->range - range1; |
| 97 | c->range = range1; |
| 98 | *state = c->one_state[*state]; |
| 99 | } |
| 100 | |
| 101 | renorm_encoder(c); |
| 102 | } |
| 103 | |
| 104 | static inline void refill(RangeCoder *c) |
| 105 | { |
| 106 | if (c->range < 0x100) { |
| 107 | c->range <<= 8; |
| 108 | c->low <<= 8; |
| 109 | if (c->bytestream < c->bytestream_end) |
| 110 | c->low += c->bytestream[0]; |
| 111 | c->bytestream++; |
| 112 | } |
| 113 | } |
| 114 | |
| 115 | static inline int get_rac(RangeCoder *c, uint8_t *const state) |
| 116 | { |
| 117 | int range1 = (c->range * (*state)) >> 8; |
| 118 | |
| 119 | c->range -= range1; |
| 120 | #if 1 |
| 121 | if (c->low < c->range) { |
| 122 | *state = c->zero_state[*state]; |
| 123 | refill(c); |
| 124 | return 0; |
| 125 | } else { |
| 126 | c->low -= c->range; |
| 127 | *state = c->one_state[*state]; |
| 128 | c->range = range1; |
| 129 | refill(c); |
| 130 | return 1; |
| 131 | } |
| 132 | #else |
| 133 | { |
| 134 | int one_mask one_mask = (c->range - c->low - 1) >> 31; |
| 135 | |
| 136 | c->low -= c->range & one_mask; |
| 137 | c->range += (range1 - c->range) & one_mask; |
| 138 | |
| 139 | *state = c->zero_state[(*state) + (256 & one_mask)]; |
| 140 | } |
| 141 | refill(c); |
| 142 | |
| 143 | return one_mask & 1; |
| 144 | #endif |
| 145 | } |
| 146 | |
| 147 | #endif /* AVCODEC_RANGECODER_H */ |