blob: 9c6ef75b69e5836475181b03a3eee8507b86aa83
| 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 | * based upon |
| 26 | * "Range encoding: an algorithm for removing redundancy from a digitised |
| 27 | * message. |
| 28 | * G. N. N. Martin Presented in March 1979 to the Video & |
| 29 | * Data Recording Conference, |
| 30 | * IBM UK Scientific Center held in Southampton July 24-27 1979." |
| 31 | */ |
| 32 | |
| 33 | #include <string.h> |
| 34 | |
| 35 | #include "libavutil/attributes.h" |
| 36 | #include "libavutil/avassert.h" |
| 37 | #include "libavutil/intreadwrite.h" |
| 38 | |
| 39 | #include "avcodec.h" |
| 40 | #include "rangecoder.h" |
| 41 | |
| 42 | av_cold void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size) |
| 43 | { |
| 44 | c->bytestream_start = |
| 45 | c->bytestream = buf; |
| 46 | c->bytestream_end = buf + buf_size; |
| 47 | c->low = 0; |
| 48 | c->range = 0xFF00; |
| 49 | c->outstanding_count = 0; |
| 50 | c->outstanding_byte = -1; |
| 51 | } |
| 52 | |
| 53 | av_cold void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, |
| 54 | int buf_size) |
| 55 | { |
| 56 | /* cast to avoid compiler warning */ |
| 57 | ff_init_range_encoder(c, (uint8_t *)buf, buf_size); |
| 58 | |
| 59 | c->low = AV_RB16(c->bytestream); |
| 60 | c->bytestream += 2; |
| 61 | } |
| 62 | |
| 63 | void ff_build_rac_states(RangeCoder *c, int factor, int max_p) |
| 64 | { |
| 65 | const int64_t one = 1LL << 32; |
| 66 | int64_t p; |
| 67 | int last_p8, p8, i; |
| 68 | |
| 69 | memset(c->zero_state, 0, sizeof(c->zero_state)); |
| 70 | memset(c->one_state, 0, sizeof(c->one_state)); |
| 71 | |
| 72 | last_p8 = 0; |
| 73 | p = one / 2; |
| 74 | for (i = 0; i < 128; i++) { |
| 75 | p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one |
| 76 | if (p8 <= last_p8) |
| 77 | p8 = last_p8 + 1; |
| 78 | if (last_p8 && last_p8 < 256 && p8 <= max_p) |
| 79 | c->one_state[last_p8] = p8; |
| 80 | |
| 81 | p += ((one - p) * factor + one / 2) >> 32; |
| 82 | last_p8 = p8; |
| 83 | } |
| 84 | |
| 85 | for (i = 256 - max_p; i <= max_p; i++) { |
| 86 | if (c->one_state[i]) |
| 87 | continue; |
| 88 | |
| 89 | p = (i * one + 128) >> 8; |
| 90 | p += ((one - p) * factor + one / 2) >> 32; |
| 91 | p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one |
| 92 | if (p8 <= i) |
| 93 | p8 = i + 1; |
| 94 | if (p8 > max_p) |
| 95 | p8 = max_p; |
| 96 | c->one_state[i] = p8; |
| 97 | } |
| 98 | |
| 99 | for (i = 1; i < 255; i++) |
| 100 | c->zero_state[i] = 256 - c->one_state[256 - i]; |
| 101 | } |
| 102 | |
| 103 | /* Return the number of bytes written. */ |
| 104 | int ff_rac_terminate(RangeCoder *c) |
| 105 | { |
| 106 | c->range = 0xFF; |
| 107 | c->low += 0xFF; |
| 108 | renorm_encoder(c); |
| 109 | c->range = 0xFF; |
| 110 | renorm_encoder(c); |
| 111 | |
| 112 | av_assert1(c->low == 0); |
| 113 | av_assert1(c->range >= 0x100); |
| 114 | |
| 115 | return c->bytestream - c->bytestream_start; |
| 116 | } |
| 117 |