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 30static 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 45static 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 71void ff_mqc_initdec(MqcState *mqc, uint8_t *bp) 72{ 73 ff_mqc_init_contexts(mqc); 74 mqc->bp = bp; 75 mqc->c = (*mqc->bp ^ 0xff) << 16; 76 bytein(mqc); 77 mqc->c = mqc->c << 7; 78 mqc->a = 0x8000; 79} 80 81int ff_mqc_decode(MqcState *mqc, uint8_t *cxstate) 82{ 83 mqc->a -= ff_mqc_qe[*cxstate]; 84 if ((mqc->c >> 16) < mqc->a) { 85 if (mqc->a & 0x8000) 86 return *cxstate & 1; 87 else 88 return exchange(mqc, cxstate, 0); 89 } else { 90 mqc->c -= mqc->a << 16; 91 return exchange(mqc, cxstate, 1); 92 } 93} 94