libavutil/crc.c

   1 /*
   2  * copyright (c) 2006 Michael Niedermayer <michaelni@gmx.at>
   3  *
   4  * This file is part of FFmpeg.
   5  *
   6  * FFmpeg is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU Lesser General Public
   8  * License as published by the Free Software Foundation; either
   9  * version 2.1 of the License, or (at your option) any later version.
  10  *
  11  * FFmpeg is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14  * Lesser General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU Lesser General Public
  17  * License along with FFmpeg; if not, write to the Free Software
  18  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  19  */
  20
  21 #include "common.h"
  22 #include "crc.h"
  23
  24 #ifdef CONFIG_HARDCODED_TABLES
  25 #include "crc_data.h"
  26 #else
  27 static struct {
  28     uint8_t  le;
  29     uint8_t  bits;
  30     uint32_t poly;
  31 } av_crc_table_params[AV_CRC_MAX] = {
  32     [AV_CRC_8_ATM]      = { 0,  8,       0x07 },
  33     [AV_CRC_16_ANSI]    = { 0, 16,     0x8005 },
  34     [AV_CRC_16_CCITT]   = { 0, 16,     0x1021 },
  35     [AV_CRC_32_IEEE]    = { 0, 32, 0x04C11DB7 },
  36     [AV_CRC_32_IEEE_LE] = { 1, 32, 0xEDB88320 },
  37 };
  38 static AVCRC av_crc_table[AV_CRC_MAX][257];
  39 #endif
  40
  41 /**
  42  * Inits a crc table.
  43  * @param ctx must be an array of sizeof(AVCRC)*257 or sizeof(AVCRC)*1024
  44  * @param cts_size size of ctx in bytes
  45  * @param le if 1, lowest bit represents coefficient for highest exponent
  46  *           of corresponding polynomial (both for poly and actual CRC).
  47  *           If 0, you must swap the crc parameter and the result of av_crc
  48  *           if you need the standard representation (can be simplified in
  49  *           most cases to e.g. bswap16):
  50  *           bswap_32(crc << (32-bits))
  51  * @param bits number of bits for the CRC
  52  * @param poly generator polynomial without the x**bits coefficient, in the
  53  *             representation as specified by le
  54  * @return <0 on failure
  55  */
  56 int av_crc_init(AVCRC *ctx, int le, int bits, uint32_t poly, int ctx_size){
  57     int i, j;
  58     uint32_t c;
  59
  60     if (bits < 8 || bits > 32 || poly >= (1LL<<bits))
  61         return -1;
  62     if (ctx_size != sizeof(AVCRC)*257 && ctx_size != sizeof(AVCRC)*1024)
  63         return -1;
  64
  65     for (i = 0; i < 256; i++) {
  66         if (le) {
  67             for (c = i, j = 0; j < 8; j++)
  68                 c = (c>>1)^(poly & (-(c&1)));
  69             ctx[i] = c;
  70         } else {
  71             for (c = i << 24, j = 0; j < 8; j++)
  72                 c = (c<<1) ^ ((poly<<(32-bits)) & (((int32_t)c)>>31) );
  73             ctx[i] = bswap_32(c);
  74         }
  75     }
  76     ctx[256]=1;
  77 #ifndef CONFIG_SMALL
  78     if(ctx_size >= sizeof(AVCRC)*1024)
  79         for (i = 0; i < 256; i++)
  80             for(j=0; j<3; j++)
  81                 ctx[256*(j+1) + i]= (ctx[256*j + i]>>8) ^ ctx[ ctx[256*j + i]&0xFF ];
  82 #endif
  83
  84     return 0;
  85 }
  86
  87 /**
  88  * Get an initialized standard CRC table.
  89  * @param crc_id ID of a standard CRC
  90  * @return a pointer to the CRC table or NULL on failure
  91  */
  92 const AVCRC *av_crc_get_table(AVCRCId crc_id){
  93 #ifndef CONFIG_HARDCODED_TABLES
  94     if (!av_crc_table[crc_id][sizeof(av_crc_table[crc_id])/sizeof(av_crc_table[crc_id][0])-1])
  95         if (av_crc_init(av_crc_table[crc_id],
  96                         av_crc_table_params[crc_id].le,
  97                         av_crc_table_params[crc_id].bits,
  98                         av_crc_table_params[crc_id].poly,
  99                         sizeof(av_crc_table[crc_id])) < 0)
 100             return NULL;
 101 #endif
 102     return av_crc_table[crc_id];
 103 }
 104
 105 /**
 106  * Calculate the CRC of a block
 107  * @param crc CRC of previous blocks if any or initial value for CRC.
 108  * @return CRC updated with the data from the given block
 109  *
 110  * @see av_crc_init() "le" parameter
 111  */
 112 uint32_t av_crc(const AVCRC *ctx, uint32_t crc, const uint8_t *buffer, size_t length){
 113     const uint8_t *end= buffer+length;
 114
 115 #ifndef CONFIG_SMALL
 116     if(!ctx[256])
 117         while(buffer<end-3){
 118             crc ^= le2me_32(*(const uint32_t*)buffer); buffer+=4;
 119             crc =  ctx[3*256 + ( crc     &0xFF)]
 120                   ^ctx[2*256 + ((crc>>8 )&0xFF)]
 121                   ^ctx[1*256 + ((crc>>16)&0xFF)]
 122                   ^ctx[0*256 + ((crc>>24)     )];
 123         }
 124 #endif
 125     while(buffer<end)
 126         crc = ctx[((uint8_t)crc) ^ *buffer++] ^ (crc >> 8);
 127
 128     return crc;
 129 }
 130
 131 #ifdef TEST
 132 #undef printf
 133 int main(void){
 134     uint8_t buf[1999];
 135     int i;
 136     int p[4][3]={{AV_CRC_32_IEEE_LE, 0xEDB88320, 0x3D5CDD04},
 137                  {AV_CRC_32_IEEE   , 0x04C11DB7, 0xC0F5BAE0},
 138                  {AV_CRC_16_ANSI   , 0x8005,     0x1FBB    },
 139                  {AV_CRC_8_ATM     , 0x07,       0xE3      },};
 140     const AVCRC *ctx;
 141
 142     for(i=0; i<sizeof(buf); i++)
 143         buf[i]= i+i*i;
 144
 145     for(i=0; i<4; i++){
 146         ctx = av_crc_get_table(p[i][0]);
 147         printf("crc %08X =%X\n", p[i][1], av_crc(ctx, 0, buf, sizeof(buf)));
 148     }
 149     return 0;
 150 }
 151 #endif