blob: 34aa51951ebdcd2f8a4e702cda5a967af48d6dcf
| 1 | /* |
| 2 | * MQ-coder decoder |
| 3 | * Copyright (c) 2007 Kamil Nowosad |
| 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 | * MQ-coder decoder |
| 24 | * @file |
| 25 | * @author Kamil Nowosad |
| 26 | */ |
| 27 | |
| 28 | #include "mqc.h" |
| 29 | |
| 30 | static void bytein(MqcState *mqc) |
| 31 | { |
| 32 | if (*mqc->bp == 0xff) { |
| 33 | if (*(mqc->bp + 1) > 0x8f) |
| 34 | mqc->c++; |
| 35 | else { |
| 36 | mqc->bp++; |
| 37 | mqc->c += 2 + 0xfe00 - (*mqc->bp << 9); |
| 38 | } |
| 39 | } else { |
| 40 | mqc->bp++; |
| 41 | mqc->c += 1 + 0xff00 - (*mqc->bp << 8); |
| 42 | } |
| 43 | } |
| 44 | |
| 45 | static int exchange(MqcState *mqc, uint8_t *cxstate, int lps) |
| 46 | { |
| 47 | int d; |
| 48 | if ((mqc->a < ff_mqc_qe[*cxstate]) ^ (!lps)) { |
| 49 | if (lps) |
| 50 | mqc->a = ff_mqc_qe[*cxstate]; |
| 51 | d = *cxstate & 1; |
| 52 | *cxstate = ff_mqc_nmps[*cxstate]; |
| 53 | } else { |
| 54 | if (lps) |
| 55 | mqc->a = ff_mqc_qe[*cxstate]; |
| 56 | d = 1 - (*cxstate & 1); |
| 57 | *cxstate = ff_mqc_nlps[*cxstate]; |
| 58 | } |
| 59 | // do RENORMD: see ISO/IEC 15444-1:2002 §C.3.3 |
| 60 | do { |
| 61 | if (!(mqc->c & 0xff)) { |
| 62 | mqc->c -= 0x100; |
| 63 | bytein(mqc); |
| 64 | } |
| 65 | mqc->a += mqc->a; |
| 66 | mqc->c += mqc->c; |
| 67 | } while (!(mqc->a & 0x8000)); |
| 68 | return d; |
| 69 | } |
| 70 | |
| 71 | void ff_mqc_initdec(MqcState *mqc, uint8_t *bp, int raw, int reset) |
| 72 | { |
| 73 | mqc->raw = raw; |
| 74 | if (reset) |
| 75 | ff_mqc_init_contexts(mqc); |
| 76 | mqc->bp = bp; |
| 77 | mqc->c = (*mqc->bp ^ 0xff) << 16; |
| 78 | bytein(mqc); |
| 79 | mqc->c = mqc->c << 7; |
| 80 | mqc->a = 0x8000; |
| 81 | } |
| 82 | |
| 83 | static int mqc_decode_bypass(MqcState *mqc) { |
| 84 | int bit = !(mqc->c & 0x40000000); |
| 85 | if (!(mqc->c & 0xff)) { |
| 86 | mqc->c -= 0x100; |
| 87 | bytein(mqc); |
| 88 | } |
| 89 | mqc->c += mqc->c; |
| 90 | return bit; |
| 91 | } |
| 92 | |
| 93 | int ff_mqc_decode(MqcState *mqc, uint8_t *cxstate) |
| 94 | { |
| 95 | if (mqc->raw) |
| 96 | return mqc_decode_bypass(mqc); |
| 97 | mqc->a -= ff_mqc_qe[*cxstate]; |
| 98 | if ((mqc->c >> 16) < mqc->a) { |
| 99 | if (mqc->a & 0x8000) |
| 100 | return *cxstate & 1; |
| 101 | else |
| 102 | return exchange(mqc, cxstate, 0); |
| 103 | } else { |
| 104 | mqc->c -= mqc->a << 16; |
| 105 | return exchange(mqc, cxstate, 1); |
| 106 | } |
| 107 | } |
| 108 |