blob: 97221dffebcc43e97b326c3817171d651dfe5e25
| 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 "bswap.h" |
| 22 | #include "crc.h" |
| 23 | |
| 24 | #if 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 | * Initializes a CRC table. |
| 43 | * @param ctx must be an array of size sizeof(AVCRC)*257 or sizeof(AVCRC)*1024 |
| 44 | * @param cts_size size of ctx in bytes |
| 45 | * @param le If 1, the lowest bit represents the coefficient for the highest |
| 46 | * exponent of the corresponding polynomial (both for poly and |
| 47 | * actual CRC). |
| 48 | * If 0, you must swap the CRC parameter and the result of av_crc |
| 49 | * if you need the standard representation (can be simplified in |
| 50 | * most cases to e.g. bswap16): |
| 51 | * bswap_32(crc << (32-bits)) |
| 52 | * @param bits number of bits for the CRC |
| 53 | * @param poly generator polynomial without the x**bits coefficient, in the |
| 54 | * representation as specified by le |
| 55 | * @return <0 on failure |
| 56 | */ |
| 57 | int av_crc_init(AVCRC *ctx, int le, int bits, uint32_t poly, int ctx_size) |
| 58 | { |
| 59 | int i, j; |
| 60 | uint32_t c; |
| 61 | |
| 62 | if (bits < 8 || bits > 32 || poly >= (1LL << bits)) { |
| 63 | return -1; |
| 64 | } |
| 65 | if (ctx_size != sizeof(AVCRC) * 257 && ctx_size != sizeof(AVCRC) * 1024) { |
| 66 | return -1; |
| 67 | } |
| 68 | |
| 69 | for (i = 0; i < 256; i++) { |
| 70 | if (le) { |
| 71 | for (c = i, j = 0; j < 8; j++) { |
| 72 | c = (c >> 1) ^(poly & (-(c & 1))); |
| 73 | } |
| 74 | ctx[i] = c; |
| 75 | } else { |
| 76 | for (c = i << 24, j = 0; j < 8; j++) { |
| 77 | c = (c << 1) ^((poly << (32 - bits)) & (((int32_t)c) >> 31)); |
| 78 | } |
| 79 | ctx[i] = bswap_32(c); |
| 80 | } |
| 81 | } |
| 82 | ctx[256] = 1; |
| 83 | //#if !CONFIG_SMALL |
| 84 | if (ctx_size >= sizeof(AVCRC) * 1024) |
| 85 | for (i = 0; i < 256; i++) |
| 86 | for (j = 0; j < 3; j++) { |
| 87 | ctx[256 * (j + 1) + i] = (ctx[256 * j + i] >> 8) ^ ctx[ ctx[256 * j + i] & 0xFF ]; |
| 88 | } |
| 89 | //#endif |
| 90 | |
| 91 | return 0; |
| 92 | } |
| 93 | |
| 94 | /** |
| 95 | * Gets an initialized standard CRC table. |
| 96 | * @param crc_id ID of a standard CRC |
| 97 | * @return a pointer to the CRC table or NULL on failure |
| 98 | */ |
| 99 | const AVCRC *av_crc_get_table(AVCRCId crc_id) |
| 100 | { |
| 101 | //#if !CONFIG_HARDCODED_TABLES |
| 102 | if (!av_crc_table[crc_id][FF_ARRAY_ELEMS(av_crc_table[crc_id]) - 1]) |
| 103 | if (av_crc_init(av_crc_table[crc_id], |
| 104 | av_crc_table_params[crc_id].le, |
| 105 | av_crc_table_params[crc_id].bits, |
| 106 | av_crc_table_params[crc_id].poly, |
| 107 | sizeof(av_crc_table[crc_id])) < 0) { |
| 108 | return NULL; |
| 109 | } |
| 110 | //#endif |
| 111 | return av_crc_table[crc_id]; |
| 112 | } |
| 113 | |
| 114 | /** |
| 115 | * Calculates the CRC of a block. |
| 116 | * @param crc CRC of previous blocks if any or initial value for CRC |
| 117 | * @return CRC updated with the data from the given block |
| 118 | * |
| 119 | * @see av_crc_init() "le" parameter |
| 120 | */ |
| 121 | uint32_t av_crc(const AVCRC *ctx, uint32_t crc, const uint8_t *buffer, size_t length) |
| 122 | { |
| 123 | const uint8_t *end = buffer + length; |
| 124 | |
| 125 | //#if !CONFIG_SMALL |
| 126 | if (!ctx[256]) { |
| 127 | while (((intptr_t) buffer & 3) && buffer < end) { |
| 128 | crc = ctx[((uint8_t)crc) ^ *buffer++] ^(crc >> 8); |
| 129 | } |
| 130 | |
| 131 | while (buffer < end - 3) { |
| 132 | crc ^= le2me_32(*(const uint32_t*)buffer); |
| 133 | buffer += 4; |
| 134 | crc = ctx[3 * 256 + (crc & 0xFF)] |
| 135 | ^ ctx[2 * 256 + ((crc >> 8) & 0xFF)] |
| 136 | ^ ctx[1 * 256 + ((crc >> 16) & 0xFF)] |
| 137 | ^ ctx[0 * 256 + ((crc >> 24))]; |
| 138 | } |
| 139 | } |
| 140 | //#endif |
| 141 | while (buffer < end) { |
| 142 | crc = ctx[((uint8_t)crc) ^ *buffer++] ^(crc >> 8); |
| 143 | } |
| 144 | |
| 145 | return crc; |
| 146 | } |
| 147 |