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libavutil/crc.c

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00001 /*
00002  * copyright (c) 2006 Michael Niedermayer <michaelni@gmx.at>
00003  *
00004  * This file is part of FFmpeg.
00005  *
00006  * FFmpeg is free software; you can redistribute it and/or
00007  * modify it under the terms of the GNU Lesser General Public
00008  * License as published by the Free Software Foundation; either
00009  * version 2.1 of the License, or (at your option) any later version.
00010  *
00011  * FFmpeg is distributed in the hope that it will be useful,
00012  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00013  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00014  * Lesser General Public License for more details.
00015  *
00016  * You should have received a copy of the GNU Lesser General Public
00017  * License along with FFmpeg; if not, write to the Free Software
00018  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
00019  */
00020 
00021 #include "config.h"
00022 #include "common.h"
00023 #include "bswap.h"
00024 #include "crc.h"
00025 
00026 #if CONFIG_HARDCODED_TABLES
00027 #include "crc_data.h"
00028 #else
00029 static struct {
00030     uint8_t  le;
00031     uint8_t  bits;
00032     uint32_t poly;
00033 } av_crc_table_params[AV_CRC_MAX] = {
00034     [AV_CRC_8_ATM]      = { 0,  8,       0x07 },
00035     [AV_CRC_16_ANSI]    = { 0, 16,     0x8005 },
00036     [AV_CRC_16_CCITT]   = { 0, 16,     0x1021 },
00037     [AV_CRC_32_IEEE]    = { 0, 32, 0x04C11DB7 },
00038     [AV_CRC_32_IEEE_LE] = { 1, 32, 0xEDB88320 },
00039 };
00040 static AVCRC av_crc_table[AV_CRC_MAX][257];
00041 #endif
00042 
00059 int av_crc_init(AVCRC *ctx, int le, int bits, uint32_t poly, int ctx_size){
00060     int i, j;
00061     uint32_t c;
00062 
00063     if (bits < 8 || bits > 32 || poly >= (1LL<<bits))
00064         return -1;
00065     if (ctx_size != sizeof(AVCRC)*257 && ctx_size != sizeof(AVCRC)*1024)
00066         return -1;
00067 
00068     for (i = 0; i < 256; i++) {
00069         if (le) {
00070             for (c = i, j = 0; j < 8; j++)
00071                 c = (c>>1)^(poly & (-(c&1)));
00072             ctx[i] = c;
00073         } else {
00074             for (c = i << 24, j = 0; j < 8; j++)
00075                 c = (c<<1) ^ ((poly<<(32-bits)) & (((int32_t)c)>>31) );
00076             ctx[i] = bswap_32(c);
00077         }
00078     }
00079     ctx[256]=1;
00080 #if !CONFIG_SMALL
00081     if(ctx_size >= sizeof(AVCRC)*1024)
00082         for (i = 0; i < 256; i++)
00083             for(j=0; j<3; j++)
00084                 ctx[256*(j+1) + i]= (ctx[256*j + i]>>8) ^ ctx[ ctx[256*j + i]&0xFF ];
00085 #endif
00086 
00087     return 0;
00088 }
00089 
00095 const AVCRC *av_crc_get_table(AVCRCId crc_id){
00096 #if !CONFIG_HARDCODED_TABLES
00097     if (!av_crc_table[crc_id][FF_ARRAY_ELEMS(av_crc_table[crc_id])-1])
00098         if (av_crc_init(av_crc_table[crc_id],
00099                         av_crc_table_params[crc_id].le,
00100                         av_crc_table_params[crc_id].bits,
00101                         av_crc_table_params[crc_id].poly,
00102                         sizeof(av_crc_table[crc_id])) < 0)
00103             return NULL;
00104 #endif
00105     return av_crc_table[crc_id];
00106 }
00107 
00115 uint32_t av_crc(const AVCRC *ctx, uint32_t crc, const uint8_t *buffer, size_t length){
00116     const uint8_t *end= buffer+length;
00117 
00118 #if !CONFIG_SMALL
00119     if(!ctx[256]) {
00120         while(((intptr_t) buffer & 3) && buffer < end)
00121             crc = ctx[((uint8_t)crc) ^ *buffer++] ^ (crc >> 8);
00122 
00123         while(buffer<end-3){
00124             crc ^= le2me_32(*(const uint32_t*)buffer); buffer+=4;
00125             crc =  ctx[3*256 + ( crc     &0xFF)]
00126                   ^ctx[2*256 + ((crc>>8 )&0xFF)]
00127                   ^ctx[1*256 + ((crc>>16)&0xFF)]
00128                   ^ctx[0*256 + ((crc>>24)     )];
00129         }
00130     }
00131 #endif
00132     while(buffer<end)
00133         crc = ctx[((uint8_t)crc) ^ *buffer++] ^ (crc >> 8);
00134 
00135     return crc;
00136 }
00137 
00138 #ifdef TEST
00139 #undef printf
00140 int main(void){
00141     uint8_t buf[1999];
00142     int i;
00143     int p[4][3]={{AV_CRC_32_IEEE_LE, 0xEDB88320, 0x3D5CDD04},
00144                  {AV_CRC_32_IEEE   , 0x04C11DB7, 0xC0F5BAE0},
00145                  {AV_CRC_16_ANSI   , 0x8005,     0x1FBB    },
00146                  {AV_CRC_8_ATM     , 0x07,       0xE3      },};
00147     const AVCRC *ctx;
00148 
00149     for(i=0; i<sizeof(buf); i++)
00150         buf[i]= i+i*i;
00151 
00152     for(i=0; i<4; i++){
00153         ctx = av_crc_get_table(p[i][0]);
00154         printf("crc %08X =%X\n", p[i][1], av_crc(ctx, 0, buf, sizeof(buf)));
00155     }
00156     return 0;
00157 }
00158 #endif

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