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 "config.h"
  22 #include "bswap.h"
  23 #include "crc.h"
  24
  25 #if CONFIG_HARDCODED_TABLES
  26 #include "crc_data.h"
  27 #else
  28 static struct {
  29     uint8_t  le;
  30     uint8_t  bits;
  31     uint32_t poly;
  32 } av_crc_table_params[AV_CRC_MAX] = {
  33     [AV_CRC_8_ATM]      = { 0,  8,       0x07 },
  34     [AV_CRC_16_ANSI]    = { 0, 16,     0x8005 },
  35     [AV_CRC_16_CCITT]   = { 0, 16,     0x1021 },
  36     [AV_CRC_32_IEEE]    = { 0, 32, 0x04C11DB7 },
  37     [AV_CRC_32_IEEE_LE] = { 1, 32, 0xEDB88320 },
  38 };
  39 static AVCRC av_crc_table[AV_CRC_MAX][257];
  40 #endif
  41
  42 /**
  43  * Initializes a CRC table.
  44  * @param ctx must be an array of size sizeof(AVCRC)*257 or sizeof(AVCRC)*1024
  45  * @param cts_size size of ctx in bytes
  46  * @param le If 1, the lowest bit represents the coefficient for the highest
  47  *           exponent of the corresponding polynomial (both for poly and
  48  *           actual CRC).
  49  *           If 0, you must swap the CRC parameter and the result of av_crc
  50  *           if you need the standard representation (can be simplified in
  51  *           most cases to e.g. bswap16):
  52  *           bswap_32(crc << (32-bits))
  53  * @param bits number of bits for the CRC
  54  * @param poly generator polynomial without the x**bits coefficient, in the
  55  *             representation as specified by le
  56  * @return <0 on failure
  57  */
  58 int av_crc_init(AVCRC *ctx, int le, int bits, uint32_t poly, int ctx_size){
  59     int i, j;
  60     uint32_t c;
  61
  62     if (bits < 8 || bits > 32 || poly >= (1LL<<bits))
  63         return -1;
  64     if (ctx_size != sizeof(AVCRC)*257 && ctx_size != sizeof(AVCRC)*1024)
  65         return -1;
  66
  67     for (i = 0; i < 256; i++) {
  68         if (le) {
  69             for (c = i, j = 0; j < 8; j++)
  70                 c = (c>>1)^(poly & (-(c&1)));
  71             ctx[i] = c;
  72         } else {
  73             for (c = i << 24, j = 0; j < 8; j++)
  74                 c = (c<<1) ^ ((poly<<(32-bits)) & (((int32_t)c)>>31) );
  75             ctx[i] = bswap_32(c);
  76         }
  77     }
  78     ctx[256]=1;
  79 #if !CONFIG_SMALL
  80     if(ctx_size >= sizeof(AVCRC)*1024)
  81         for (i = 0; i < 256; i++)
  82             for(j=0; j<3; j++)
  83                 ctx[256*(j+1) + i]= (ctx[256*j + i]>>8) ^ ctx[ ctx[256*j + i]&0xFF ];
  84 #endif
  85
  86     return 0;
  87 }
  88
  89 /**
  90  * Gets an initialized standard CRC table.
  91  * @param crc_id ID of a standard CRC
  92  * @return a pointer to the CRC table or NULL on failure
  93  */
  94 const AVCRC *av_crc_get_table(AVCRCId crc_id){
  95 #if !CONFIG_HARDCODED_TABLES
  96     if (!av_crc_table[crc_id][FF_ARRAY_ELEMS(av_crc_table[crc_id])-1])
  97         if (av_crc_init(av_crc_table[crc_id],
  98                         av_crc_table_params[crc_id].le,
  99                         av_crc_table_params[crc_id].bits,
 100                         av_crc_table_params[crc_id].poly,
 101                         sizeof(av_crc_table[crc_id])) < 0)
 102             return NULL;
 103 #endif
 104     return av_crc_table[crc_id];
 105 }
 106
 107 /**
 108  * Calculates the CRC of a block.
 109  * @param crc CRC of previous blocks if any or initial value for CRC
 110  * @return CRC updated with the data from the given block
 111  *
 112  * @see av_crc_init() "le" parameter
 113  */
 114 uint32_t av_crc(const AVCRC *ctx, uint32_t crc, const uint8_t *buffer, size_t length){
 115     const uint8_t *end= buffer+length;
 116
 117 #if !CONFIG_SMALL
 118     if(!ctx[256])
 119         while(buffer<end-3){
 120             crc ^= le2me_32(*(const uint32_t*)buffer); buffer+=4;
 121             crc =  ctx[3*256 + ( crc     &0xFF)]
 122                   ^ctx[2*256 + ((crc>>8 )&0xFF)]
 123                   ^ctx[1*256 + ((crc>>16)&0xFF)]
 124                   ^ctx[0*256 + ((crc>>24)     )];
 125         }
 126 #endif
 127     while(buffer<end)
 128         crc = ctx[((uint8_t)crc) ^ *buffer++] ^ (crc >> 8);
 129
 130     return crc;
 131 }
 132
 133 #ifdef TEST
 134 #undef printf
 135 int main(void){
 136     uint8_t buf[1999];
 137     int i;
 138     int p[4][3]={{AV_CRC_32_IEEE_LE, 0xEDB88320, 0x3D5CDD04},
 139                  {AV_CRC_32_IEEE   , 0x04C11DB7, 0xC0F5BAE0},
 140                  {AV_CRC_16_ANSI   , 0x8005,     0x1FBB    },
 141                  {AV_CRC_8_ATM     , 0x07,       0xE3      },};
 142     const AVCRC *ctx;
 143
 144     for(i=0; i<sizeof(buf); i++)
 145         buf[i]= i+i*i;
 146
 147     for(i=0; i<4; i++){
 148         ctx = av_crc_get_table(p[i][0]);
 149         printf("crc %08X =%X\n", p[i][1], av_crc(ctx, 0, buf, sizeof(buf)));
 150     }
 151     return 0;
 152 }
 153 #endif