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libavcodec/mlp.c

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00001 /*
00002  * MLP codec common code
00003  * Copyright (c) 2007-2008 Ian Caulfield
00004  *
00005  * This file is part of FFmpeg.
00006  *
00007  * FFmpeg is free software; you can redistribute it and/or
00008  * modify it under the terms of the GNU Lesser General Public
00009  * License as published by the Free Software Foundation; either
00010  * version 2.1 of the License, or (at your option) any later version.
00011  *
00012  * FFmpeg is distributed in the hope that it will be useful,
00013  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00014  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00015  * Lesser General Public License for more details.
00016  *
00017  * You should have received a copy of the GNU Lesser General Public
00018  * License along with FFmpeg; if not, write to the Free Software
00019  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
00020  */
00021 
00022 #include <stdint.h>
00023 
00024 #include "libavutil/crc.h"
00025 #include "libavutil/intreadwrite.h"
00026 #include "mlp.h"
00027 
00028 const uint8_t ff_mlp_huffman_tables[3][18][2] = {
00029     {    /* Huffman table 0, -7 - +10 */
00030         {0x01, 9}, {0x01, 8}, {0x01, 7}, {0x01, 6}, {0x01, 5}, {0x01, 4}, {0x01, 3},
00031         {0x04, 3}, {0x05, 3}, {0x06, 3}, {0x07, 3},
00032         {0x03, 3}, {0x05, 4}, {0x09, 5}, {0x11, 6}, {0x21, 7}, {0x41, 8}, {0x81, 9},
00033     }, { /* Huffman table 1, -7 - +8 */
00034         {0x01, 9}, {0x01, 8}, {0x01, 7}, {0x01, 6}, {0x01, 5}, {0x01, 4}, {0x01, 3},
00035         {0x02, 2}, {0x03, 2},
00036         {0x03, 3}, {0x05, 4}, {0x09, 5}, {0x11, 6}, {0x21, 7}, {0x41, 8}, {0x81, 9},
00037     }, { /* Huffman table 2, -7 - +7 */
00038         {0x01, 9}, {0x01, 8}, {0x01, 7}, {0x01, 6}, {0x01, 5}, {0x01, 4}, {0x01, 3},
00039         {0x01, 1},
00040         {0x03, 3}, {0x05, 4}, {0x09, 5}, {0x11, 6}, {0x21, 7}, {0x41, 8}, {0x81, 9},
00041     }
00042 };
00043 
00044 static int crc_init = 0;
00045 static AVCRC crc_63[1024];
00046 static AVCRC crc_1D[1024];
00047 static AVCRC crc_2D[1024];
00048 
00049 av_cold void ff_mlp_init_crc(void)
00050 {
00051     if (!crc_init) {
00052         av_crc_init(crc_63, 0,  8,   0x63, sizeof(crc_63));
00053         av_crc_init(crc_1D, 0,  8,   0x1D, sizeof(crc_1D));
00054         av_crc_init(crc_2D, 0, 16, 0x002D, sizeof(crc_2D));
00055         crc_init = 1;
00056     }
00057 }
00058 
00059 uint16_t ff_mlp_checksum16(const uint8_t *buf, unsigned int buf_size)
00060 {
00061     uint16_t crc;
00062 
00063     crc = av_crc(crc_2D, 0, buf, buf_size - 2);
00064     crc ^= AV_RL16(buf + buf_size - 2);
00065     return crc;
00066 }
00067 
00068 uint8_t ff_mlp_checksum8(const uint8_t *buf, unsigned int buf_size)
00069 {
00070     uint8_t checksum = av_crc(crc_63, 0x3c, buf, buf_size - 1); // crc_63[0xa2] == 0x3c
00071     checksum ^= buf[buf_size-1];
00072     return checksum;
00073 }
00074 
00075 uint8_t ff_mlp_restart_checksum(const uint8_t *buf, unsigned int bit_size)
00076 {
00077     int i;
00078     int num_bytes = (bit_size + 2) / 8;
00079 
00080     int crc = crc_1D[buf[0] & 0x3f];
00081     crc = av_crc(crc_1D, crc, buf + 1, num_bytes - 2);
00082     crc ^= buf[num_bytes - 1];
00083 
00084     for (i = 0; i < ((bit_size + 2) & 7); i++) {
00085         crc <<= 1;
00086         if (crc & 0x100)
00087             crc ^= 0x11D;
00088         crc ^= (buf[num_bytes] >> (7 - i)) & 1;
00089     }
00090 
00091     return crc;
00092 }
00093 
00094 uint8_t ff_mlp_calculate_parity(const uint8_t *buf, unsigned int buf_size)
00095 {
00096     uint32_t scratch = 0;
00097     const uint8_t *buf_end = buf + buf_size;
00098 
00099     for (; buf < buf_end - 3; buf += 4)
00100         scratch ^= *((const uint32_t*)buf);
00101 
00102     scratch = xor_32_to_8(scratch);
00103 
00104     for (; buf < buf_end; buf++)
00105         scratch ^= *buf;
00106 
00107     return scratch;
00108 }

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