/* * copyright (c) 2006 Michael Niedermayer <michaelni@gmx.at> * * This file is part of Libav. * * Libav 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. * * Libav 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 Libav; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */ #include "config.h" #include "common.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 /** * Initialize a CRC table. * @param ctx must be an array of size sizeof(AVCRC)*257 or sizeof(AVCRC)*1024 * @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): * av_bswap32(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 * @param ctx_size size of ctx in bytes * @return <0 on failure */ int av_crc_init(AVCRC *ctx, int le, int bits, uint32_t poly, int ctx_size) { unsigned 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] = av_bswap32(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; } /** * Get 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]; } /** * Calculate 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 (((intptr_t) buffer & 3) && buffer < end) crc = ctx[((uint8_t) crc) ^ *buffer++] ^ (crc >> 8); while (buffer < end - 3) { crc ^= av_le2ne32(*(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