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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 Libav.
00005  *
00006  * Libav 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  * Libav 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 Libav; 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 {
00061     unsigned i, j;
00062     uint32_t c;
00063 
00064     if (bits < 8 || bits > 32 || poly >= (1LL << bits))
00065         return -1;
00066     if (ctx_size != sizeof(AVCRC) * 257 && ctx_size != sizeof(AVCRC) * 1024)
00067         return -1;
00068 
00069     for (i = 0; i < 256; i++) {
00070         if (le) {
00071             for (c = i, j = 0; j < 8; j++)
00072                 c = (c >> 1) ^ (poly & (-(c & 1)));
00073             ctx[i] = c;
00074         } else {
00075             for (c = i << 24, j = 0; j < 8; j++)
00076                 c = (c << 1) ^ ((poly << (32 - bits)) & (((int32_t) c) >> 31));
00077             ctx[i] = av_bswap32(c);
00078         }
00079     }
00080     ctx[256] = 1;
00081 #if !CONFIG_SMALL
00082     if (ctx_size >= sizeof(AVCRC) * 1024)
00083         for (i = 0; i < 256; i++)
00084             for (j = 0; j < 3; j++)
00085                 ctx[256 *(j + 1) + i] =
00086                     (ctx[256 * j + i] >> 8) ^ ctx[ctx[256 * j + i] & 0xFF];
00087 #endif
00088 
00089     return 0;
00090 }
00091 
00097 const AVCRC *av_crc_get_table(AVCRCId crc_id)
00098 {
00099 #if !CONFIG_HARDCODED_TABLES
00100     if (!av_crc_table[crc_id][FF_ARRAY_ELEMS(av_crc_table[crc_id]) - 1])
00101         if (av_crc_init(av_crc_table[crc_id],
00102                         av_crc_table_params[crc_id].le,
00103                         av_crc_table_params[crc_id].bits,
00104                         av_crc_table_params[crc_id].poly,
00105                         sizeof(av_crc_table[crc_id])) < 0)
00106             return NULL;
00107 #endif
00108     return av_crc_table[crc_id];
00109 }
00110 
00118 uint32_t av_crc(const AVCRC *ctx, uint32_t crc,
00119                 const uint8_t *buffer, size_t length)
00120 {
00121     const uint8_t *end = buffer + length;
00122 
00123 #if !CONFIG_SMALL
00124     if (!ctx[256]) {
00125         while (((intptr_t) buffer & 3) && buffer < end)
00126             crc = ctx[((uint8_t) crc) ^ *buffer++] ^ (crc >> 8);
00127 
00128         while (buffer < end - 3) {
00129             crc ^= av_le2ne32(*(const uint32_t *) buffer); buffer += 4;
00130             crc = ctx[3 * 256 + ( crc        & 0xFF)] ^
00131                   ctx[2 * 256 + ((crc >> 8 ) & 0xFF)] ^
00132                   ctx[1 * 256 + ((crc >> 16) & 0xFF)] ^
00133                   ctx[0 * 256 + ((crc >> 24)       )];
00134         }
00135     }
00136 #endif
00137     while (buffer < end)
00138         crc = ctx[((uint8_t) crc) ^ *buffer++] ^ (crc >> 8);
00139 
00140     return crc;
00141 }
00142 
00143 #ifdef TEST
00144 #undef printf
00145 int main(void)
00146 {
00147     uint8_t buf[1999];
00148     int i;
00149     int p[4][3] = { { AV_CRC_32_IEEE_LE, 0xEDB88320, 0x3D5CDD04 },
00150                     { AV_CRC_32_IEEE   , 0x04C11DB7, 0xC0F5BAE0 },
00151                     { AV_CRC_16_ANSI   , 0x8005    , 0x1FBB     },
00152                     { AV_CRC_8_ATM     , 0x07      , 0xE3       }
00153     };
00154     const AVCRC *ctx;
00155 
00156     for (i = 0; i < sizeof(buf); i++)
00157         buf[i] = i + i * i;
00158 
00159     for (i = 0; i < 4; i++) {
00160         ctx = av_crc_get_table(p[i][0]);
00161         printf("crc %08X = %X\n", p[i][1], av_crc(ctx, 0, buf, sizeof(buf)));
00162     }
00163     return 0;
00164 }
00165 #endif
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