hash.h (8457B)
1 /* 2 * Copyright (C) 2013 Reimar Döffinger <Reimar.Doeffinger@gmx.de> 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 /** 22 * @file 23 * @ingroup lavu_hash_generic 24 * Generic hashing API 25 */ 26 27 #ifndef AVUTIL_HASH_H 28 #define AVUTIL_HASH_H 29 30 #include <stddef.h> 31 #include <stdint.h> 32 33 /** 34 * @defgroup lavu_hash Hash Functions 35 * @ingroup lavu_crypto 36 * Hash functions useful in multimedia. 37 * 38 * Hash functions are widely used in multimedia, from error checking and 39 * concealment to internal regression testing. libavutil has efficient 40 * implementations of a variety of hash functions that may be useful for 41 * FFmpeg and other multimedia applications. 42 * 43 * @{ 44 * 45 * @defgroup lavu_hash_generic Generic Hashing API 46 * An abstraction layer for all hash functions supported by libavutil. 47 * 48 * If your application needs to support a wide range of different hash 49 * functions, then the Generic Hashing API is for you. It provides a generic, 50 * reusable API for @ref lavu_hash "all hash functions" implemented in libavutil. 51 * If you just need to use one particular hash function, use the @ref lavu_hash 52 * "individual hash" directly. 53 * 54 * @section Sample Code 55 * 56 * A basic template for using the Generic Hashing API follows: 57 * 58 * @code 59 * struct AVHashContext *ctx = NULL; 60 * const char *hash_name = NULL; 61 * uint8_t *output_buf = NULL; 62 * 63 * // Select from a string returned by av_hash_names() 64 * hash_name = ...; 65 * 66 * // Allocate a hash context 67 * ret = av_hash_alloc(&ctx, hash_name); 68 * if (ret < 0) 69 * return ret; 70 * 71 * // Initialize the hash context 72 * av_hash_init(ctx); 73 * 74 * // Update the hash context with data 75 * while (data_left) { 76 * av_hash_update(ctx, data, size); 77 * } 78 * 79 * // Now we have no more data, so it is time to finalize the hash and get the 80 * // output. But we need to first allocate an output buffer. Note that you can 81 * // use any memory allocation function, including malloc(), not just 82 * // av_malloc(). 83 * output_buf = av_malloc(av_hash_get_size(ctx)); 84 * if (!output_buf) 85 * return AVERROR(ENOMEM); 86 * 87 * // Finalize the hash context. 88 * // You can use any of the av_hash_final*() functions provided, for other 89 * // output formats. If you do so, be sure to adjust the memory allocation 90 * // above. See the function documentation below for the exact amount of extra 91 * // memory needed. 92 * av_hash_final(ctx, output_buffer); 93 * 94 * // Free the context 95 * av_hash_freep(&ctx); 96 * @endcode 97 * 98 * @section Hash Function-Specific Information 99 * If the CRC32 hash is selected, the #AV_CRC_32_IEEE polynomial will be 100 * used. 101 * 102 * If the Murmur3 hash is selected, the default seed will be used. See @ref 103 * lavu_murmur3_seedinfo "Murmur3" for more information. 104 * 105 * @{ 106 */ 107 108 /** 109 * @example ffhash.c 110 * This example is a simple command line application that takes one or more 111 * arguments. It demonstrates a typical use of the hashing API with allocation, 112 * initialization, updating, and finalizing. 113 */ 114 115 struct AVHashContext; 116 117 /** 118 * Allocate a hash context for the algorithm specified by name. 119 * 120 * @return >= 0 for success, a negative error code for failure 121 * 122 * @note The context is not initialized after a call to this function; you must 123 * call av_hash_init() to do so. 124 */ 125 int av_hash_alloc(struct AVHashContext **ctx, const char *name); 126 127 /** 128 * Get the names of available hash algorithms. 129 * 130 * This function can be used to enumerate the algorithms. 131 * 132 * @param[in] i Index of the hash algorithm, starting from 0 133 * @return Pointer to a static string or `NULL` if `i` is out of range 134 */ 135 const char *av_hash_names(int i); 136 137 /** 138 * Get the name of the algorithm corresponding to the given hash context. 139 */ 140 const char *av_hash_get_name(const struct AVHashContext *ctx); 141 142 /** 143 * Maximum value that av_hash_get_size() will currently return. 144 * 145 * You can use this if you absolutely want or need to use static allocation for 146 * the output buffer and are fine with not supporting hashes newly added to 147 * libavutil without recompilation. 148 * 149 * @warning 150 * Adding new hashes with larger sizes, and increasing the macro while doing 151 * so, will not be considered an ABI change. To prevent your code from 152 * overflowing a buffer, either dynamically allocate the output buffer with 153 * av_hash_get_size(), or limit your use of the Hashing API to hashes that are 154 * already in FFmpeg during the time of compilation. 155 */ 156 #define AV_HASH_MAX_SIZE 64 157 158 /** 159 * Get the size of the resulting hash value in bytes. 160 * 161 * The maximum value this function will currently return is available as macro 162 * #AV_HASH_MAX_SIZE. 163 * 164 * @param[in] ctx Hash context 165 * @return Size of the hash value in bytes 166 */ 167 int av_hash_get_size(const struct AVHashContext *ctx); 168 169 /** 170 * Initialize or reset a hash context. 171 * 172 * @param[in,out] ctx Hash context 173 */ 174 void av_hash_init(struct AVHashContext *ctx); 175 176 /** 177 * Update a hash context with additional data. 178 * 179 * @param[in,out] ctx Hash context 180 * @param[in] src Data to be added to the hash context 181 * @param[in] len Size of the additional data 182 */ 183 void av_hash_update(struct AVHashContext *ctx, const uint8_t *src, size_t len); 184 185 /** 186 * Finalize a hash context and compute the actual hash value. 187 * 188 * The minimum size of `dst` buffer is given by av_hash_get_size() or 189 * #AV_HASH_MAX_SIZE. The use of the latter macro is discouraged. 190 * 191 * It is not safe to update or finalize a hash context again, if it has already 192 * been finalized. 193 * 194 * @param[in,out] ctx Hash context 195 * @param[out] dst Where the final hash value will be stored 196 * 197 * @see av_hash_final_bin() provides an alternative API 198 */ 199 void av_hash_final(struct AVHashContext *ctx, uint8_t *dst); 200 201 /** 202 * Finalize a hash context and store the actual hash value in a buffer. 203 * 204 * It is not safe to update or finalize a hash context again, if it has already 205 * been finalized. 206 * 207 * If `size` is smaller than the hash size (given by av_hash_get_size()), the 208 * hash is truncated; if size is larger, the buffer is padded with 0. 209 * 210 * @param[in,out] ctx Hash context 211 * @param[out] dst Where the final hash value will be stored 212 * @param[in] size Number of bytes to write to `dst` 213 */ 214 void av_hash_final_bin(struct AVHashContext *ctx, uint8_t *dst, int size); 215 216 /** 217 * Finalize a hash context and store the hexadecimal representation of the 218 * actual hash value as a string. 219 * 220 * It is not safe to update or finalize a hash context again, if it has already 221 * been finalized. 222 * 223 * The string is always 0-terminated. 224 * 225 * If `size` is smaller than `2 * hash_size + 1`, where `hash_size` is the 226 * value returned by av_hash_get_size(), the string will be truncated. 227 * 228 * @param[in,out] ctx Hash context 229 * @param[out] dst Where the string will be stored 230 * @param[in] size Maximum number of bytes to write to `dst` 231 */ 232 void av_hash_final_hex(struct AVHashContext *ctx, uint8_t *dst, int size); 233 234 /** 235 * Finalize a hash context and store the Base64 representation of the 236 * actual hash value as a string. 237 * 238 * It is not safe to update or finalize a hash context again, if it has already 239 * been finalized. 240 * 241 * The string is always 0-terminated. 242 * 243 * If `size` is smaller than AV_BASE64_SIZE(hash_size), where `hash_size` is 244 * the value returned by av_hash_get_size(), the string will be truncated. 245 * 246 * @param[in,out] ctx Hash context 247 * @param[out] dst Where the final hash value will be stored 248 * @param[in] size Maximum number of bytes to write to `dst` 249 */ 250 void av_hash_final_b64(struct AVHashContext *ctx, uint8_t *dst, int size); 251 252 /** 253 * Free hash context and set hash context pointer to `NULL`. 254 * 255 * @param[in,out] ctx Pointer to hash context 256 */ 257 void av_hash_freep(struct AVHashContext **ctx); 258 259 /** 260 * @} 261 * @} 262 */ 263 264 #endif /* AVUTIL_HASH_H */