/* * copyright (c) 2006 Michael Niedermayer <michaelni@gmx.at> * * This file is part of FFmpeg. * * FFmpeg is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 2.1 of the License, or (at your option) any later version. * * FFmpeg is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with FFmpeg; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */ #include "config.h" #include "bswap.h" #include "crc.h" #if CONFIG_HARDCODED_TABLES #include "crc_data.h" #else static struct { uint8_t le; uint8_t bits; uint32_t poly; } av_crc_table_params[AV_CRC_MAX] = { [AV_CRC_8_ATM] = { 0, 8, 0x07 }, [AV_CRC_16_ANSI] = { 0, 16, 0x8005 }, [AV_CRC_16_CCITT] = { 0, 16, 0x1021 }, [AV_CRC_32_IEEE] = { 0, 32, 0x04C11DB7 }, [AV_CRC_32_IEEE_LE] = { 1, 32, 0xEDB88320 }, }; static AVCRC av_crc_table[AV_CRC_MAX][257]; #endif /** * Initializes a CRC table. * @param ctx must be an array of size sizeof(AVCRC)*257 or sizeof(AVCRC)*1024 * @param cts_size size of ctx in bytes * @param le If 1, the lowest bit represents the coefficient for the highest * exponent of the corresponding polynomial (both for poly and * actual CRC). * If 0, you must swap the CRC parameter and the result of av_crc * if you need the standard representation (can be simplified in * most cases to e.g. bswap16): * bswap_32(crc << (32-bits)) * @param bits number of bits for the CRC * @param poly generator polynomial without the x**bits coefficient, in the * representation as specified by le * @return <0 on failure */ int av_crc_init(AVCRC *ctx, int le, int bits, uint32_t poly, int ctx_size){ int i, j; uint32_t c; if (bits < 8 || bits > 32 || poly >= (1LL<<bits)) return -1; if (ctx_size != sizeof(AVCRC)*257 && ctx_size != sizeof(AVCRC)*1024) return -1; for (i = 0; i < 256; i++) { if (le) { for (c = i, j = 0; j < 8; j++) c = (c>>1)^(poly & (-(c&1))); ctx[i] = c; } else { for (c = i << 24, j = 0; j < 8; j++) c = (c<<1) ^ ((poly<<(32-bits)) & (((int32_t)c)>>31) ); ctx[i] = bswap_32(c); } } ctx[256]=1; #if !CONFIG_SMALL if(ctx_size >= sizeof(AVCRC)*1024) for (i = 0; i < 256; i++) for(j=0; j<3; j++) ctx[256*(j+1) + i]= (ctx[256*j + i]>>8) ^ ctx[ ctx[256*j + i]&0xFF ]; #endif return 0; } /** * Gets an initialized standard CRC table. * @param crc_id ID of a standard CRC * @return a pointer to the CRC table or NULL on failure */ const AVCRC *av_crc_get_table(AVCRCId crc_id){ #if !CONFIG_HARDCODED_TABLES if (!av_crc_table[crc_id][FF_ARRAY_ELEMS(av_crc_table[crc_id])-1]) if (av_crc_init(av_crc_table[crc_id], av_crc_table_params[crc_id].le, av_crc_table_params[crc_id].bits, av_crc_table_params[crc_id].poly, sizeof(av_crc_table[crc_id])) < 0) return NULL; #endif return av_crc_table[crc_id]; } /** * Calculates the CRC of a block. * @param crc CRC of previous blocks if any or initial value for CRC * @return CRC updated with the data from the given block * * @see av_crc_init() "le" parameter */ uint32_t av_crc(const AVCRC *ctx, uint32_t crc, const uint8_t *buffer, size_t length){ const uint8_t *end= buffer+length; #if !CONFIG_SMALL if(!ctx[256]) while(buffer<end-3){ crc ^= le2me_32(*(const uint32_t*)buffer); buffer+=4; crc = ctx[3*256 + ( crc &0xFF)] ^ctx[2*256 + ((crc>>8 )&0xFF)] ^ctx[1*256 + ((crc>>16)&0xFF)] ^ctx[0*256 + ((crc>>24) )]; } #endif while(buffer<end) crc = ctx[((uint8_t)crc) ^ *buffer++] ^ (crc >> 8); return crc; } #ifdef TEST #undef printf int main(void){ uint8_t buf[1999]; int i; int p[4][3]={{AV_CRC_32_IEEE_LE, 0xEDB88320, 0x3D5CDD04}, {AV_CRC_32_IEEE , 0x04C11DB7, 0xC0F5BAE0}, {AV_CRC_16_ANSI , 0x8005, 0x1FBB }, {AV_CRC_8_ATM , 0x07, 0xE3 },}; const AVCRC *ctx; for(i=0; i<sizeof(buf); i++) buf[i]= i+i*i; for(i=0; i<4; i++){ ctx = av_crc_get_table(p[i][0]); printf("crc %08X =%X\n", p[i][1], av_crc(ctx, 0, buf, sizeof(buf))); } return 0; } #endif