| 1 | /* |
| 2 | * Lagarith range decoder |
| 3 | * Copyright (c) 2009 Nathan Caldwell <saintdev (at) gmail.com> |
| 4 | * Copyright (c) 2009 David Conrad |
| 5 | * |
| 6 | * This file is part of FFmpeg. |
| 7 | * |
| 8 | * FFmpeg is free software; you can redistribute it and/or |
| 9 | * modify it under the terms of the GNU Lesser General Public |
| 10 | * License as published by the Free Software Foundation; either |
| 11 | * version 2.1 of the License, or (at your option) any later version. |
| 12 | * |
| 13 | * FFmpeg is distributed in the hope that it will be useful, |
| 14 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 15 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| 16 | * Lesser General Public License for more details. |
| 17 | * |
| 18 | * You should have received a copy of the GNU Lesser General Public |
| 19 | * License along with FFmpeg; if not, write to the Free Software |
| 20 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA |
| 21 | */ |
| 22 | |
| 23 | /** |
| 24 | * @file |
| 25 | * Lagarith range decoder |
| 26 | * @author Nathan Caldwell |
| 27 | * @author David Conrad |
| 28 | */ |
| 29 | |
| 30 | #ifndef AVCODEC_LAGARITHRAC_H |
| 31 | #define AVCODEC_LAGARITHRAC_H |
| 32 | |
| 33 | #include <stdint.h> |
| 34 | #include "libavutil/common.h" |
| 35 | #include "libavutil/intreadwrite.h" |
| 36 | #include "avcodec.h" |
| 37 | #include "get_bits.h" |
| 38 | |
| 39 | typedef struct lag_rac { |
| 40 | AVCodecContext *avctx; |
| 41 | unsigned low; |
| 42 | unsigned range; |
| 43 | unsigned scale; /**< Number of bits of precision in range. */ |
| 44 | unsigned hash_shift; /**< Number of bits to shift to calculate hash for radix search. */ |
| 45 | |
| 46 | const uint8_t *bytestream_start; /**< Start of input bytestream. */ |
| 47 | const uint8_t *bytestream; /**< Current position in input bytestream. */ |
| 48 | const uint8_t *bytestream_end; /**< End position of input bytestream. */ |
| 49 | |
| 50 | uint32_t prob[258]; /**< Table of cumulative probability for each symbol. */ |
| 51 | uint8_t range_hash[1024]; /**< Hash table mapping upper byte to approximate symbol. */ |
| 52 | } lag_rac; |
| 53 | |
| 54 | void ff_lag_rac_init(lag_rac *l, GetBitContext *gb, int length); |
| 55 | |
| 56 | /* TODO: Optimize */ |
| 57 | static inline void lag_rac_refill(lag_rac *l) |
| 58 | { |
| 59 | while (l->range <= 0x800000) { |
| 60 | l->low <<= 8; |
| 61 | l->range <<= 8; |
| 62 | l->low |= 0xff & (AV_RB16(l->bytestream) >> 1); |
| 63 | if (l->bytestream < l->bytestream_end) |
| 64 | l->bytestream++; |
| 65 | } |
| 66 | } |
| 67 | |
| 68 | /** |
| 69 | * Decode a single byte from the compressed plane described by *l. |
| 70 | * @param l pointer to lag_rac for the current plane |
| 71 | * @return next byte of decoded data |
| 72 | */ |
| 73 | static inline uint8_t lag_get_rac(lag_rac *l) |
| 74 | { |
| 75 | unsigned range_scaled, low_scaled; |
| 76 | int val; |
| 77 | |
| 78 | lag_rac_refill(l); |
| 79 | |
| 80 | range_scaled = l->range >> l->scale; |
| 81 | |
| 82 | if (l->low < range_scaled * l->prob[255]) { |
| 83 | /* val = 0 is frequent enough to deserve a shortcut */ |
| 84 | if (l->low < range_scaled * l->prob[1]) { |
| 85 | val = 0; |
| 86 | } else { |
| 87 | low_scaled = l->low / (range_scaled<<(l->hash_shift)); |
| 88 | |
| 89 | val = l->range_hash[low_scaled]; |
| 90 | while (l->low >= range_scaled * l->prob[val + 1]) |
| 91 | val++; |
| 92 | } |
| 93 | |
| 94 | l->range = range_scaled * (l->prob[val + 1] - l->prob[val]); |
| 95 | } else { |
| 96 | val = 255; |
| 97 | l->range -= range_scaled * l->prob[255]; |
| 98 | } |
| 99 | |
| 100 | if (!l->range) |
| 101 | l->range = 0x80; |
| 102 | |
| 103 | l->low -= range_scaled * l->prob[val]; |
| 104 | |
| 105 | return val; |
| 106 | } |
| 107 | |
| 108 | |
| 109 | #endif /* AVCODEC_LAGARITHRAC_H */ |