2 * Copyright (C) 2013 Reimar Döffinger <Reimar.Doeffinger@gmx.de>
4 * This file is part of FFmpeg.
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.
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.
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
23 * @ingroup lavu_hash_generic
35 * @defgroup lavu_hash Hash Functions
36 * @ingroup lavu_crypto
37 * Hash functions useful in multimedia.
39 * Hash functions are widely used in multimedia, from error checking and
40 * concealment to internal regression testing. libavutil has efficient
41 * implementations of a variety of hash functions that may be useful for
42 * FFmpeg and other multimedia applications.
46 * @defgroup lavu_hash_generic Generic Hashing API
47 * An abstraction layer for all hash functions supported by libavutil.
49 * If your application needs to support a wide range of different hash
50 * functions, then the Generic Hashing API is for you. It provides a generic,
51 * reusable API for @ref lavu_hash "all hash functions" implemented in libavutil.
52 * If you just need to use one particular hash function, use the @ref lavu_hash
53 * "individual hash" directly.
55 * @section Sample Code
57 * A basic template for using the Generic Hashing API follows:
60 * struct AVHashContext *ctx = NULL;
61 * const char *hash_name = NULL;
62 * uint8_t *output_buf = NULL;
64 * // Select from a string returned by av_hash_names()
67 * // Allocate a hash context
68 * ret = av_hash_alloc(&ctx, hash_name);
72 * // Initialize the hash context
75 * // Update the hash context with data
77 * av_hash_update(ctx, data, size);
80 * // Now we have no more data, so it is time to finalize the hash and get the
81 * // output. But we need to first allocate an output buffer. Note that you can
82 * // use any memory allocation function, including malloc(), not just
84 * output_buf = av_malloc(av_hash_get_size(ctx));
86 * return AVERROR(ENOMEM);
88 * // Finalize the hash context.
89 * // You can use any of the av_hash_final*() functions provided, for other
90 * // output formats. If you do so, be sure to adjust the memory allocation
91 * // above. See the function documentation below for the exact amount of extra
93 * av_hash_final(ctx, output_buffer);
96 * av_hash_freep(&ctx);
99 * @section Hash Function-Specific Information
100 * If the CRC32 hash is selected, the #AV_CRC_32_IEEE polynomial will be
103 * If the Murmur3 hash is selected, the default seed will be used. See @ref
104 * lavu_murmur3_seedinfo "Murmur3" for more information.
111 * This example is a simple command line application that takes one or more
112 * arguments. It demonstrates a typical use of the hashing API with allocation,
113 * initialization, updating, and finalizing.
116 struct AVHashContext;
119 * Allocate a hash context for the algorithm specified by name.
121 * @return >= 0 for success, a negative error code for failure
123 * @note The context is not initialized after a call to this function; you must
124 * call av_hash_init() to do so.
126 int av_hash_alloc(struct AVHashContext **ctx, const char *name);
129 * Get the names of available hash algorithms.
131 * This function can be used to enumerate the algorithms.
133 * @param[in] i Index of the hash algorithm, starting from 0
134 * @return Pointer to a static string or `NULL` if `i` is out of range
136 const char *av_hash_names(int i);
139 * Get the name of the algorithm corresponding to the given hash context.
141 const char *av_hash_get_name(const struct AVHashContext *ctx);
144 * Maximum value that av_hash_get_size() will currently return.
146 * You can use this if you absolutely want or need to use static allocation for
147 * the output buffer and are fine with not supporting hashes newly added to
148 * libavutil without recompilation.
151 * Adding new hashes with larger sizes, and increasing the macro while doing
152 * so, will not be considered an ABI change. To prevent your code from
153 * overflowing a buffer, either dynamically allocate the output buffer with
154 * av_hash_get_size(), or limit your use of the Hashing API to hashes that are
155 * already in FFmpeg during the time of compilation.
157 #define AV_HASH_MAX_SIZE 64
160 * Get the size of the resulting hash value in bytes.
162 * The maximum value this function will currently return is available as macro
165 * @param[in] ctx Hash context
166 * @return Size of the hash value in bytes
168 int av_hash_get_size(const struct AVHashContext *ctx);
171 * Initialize or reset a hash context.
173 * @param[in,out] ctx Hash context
175 void av_hash_init(struct AVHashContext *ctx);
178 * Update a hash context with additional data.
180 * @param[in,out] ctx Hash context
181 * @param[in] src Data to be added to the hash context
182 * @param[in] len Size of the additional data
184 #if FF_API_CRYPTO_SIZE_T
185 void av_hash_update(struct AVHashContext *ctx, const uint8_t *src, int len);
187 void av_hash_update(struct AVHashContext *ctx, const uint8_t *src, size_t len);
191 * Finalize a hash context and compute the actual hash value.
193 * The minimum size of `dst` buffer is given by av_hash_get_size() or
194 * #AV_HASH_MAX_SIZE. The use of the latter macro is discouraged.
196 * It is not safe to update or finalize a hash context again, if it has already
199 * @param[in,out] ctx Hash context
200 * @param[out] dst Where the final hash value will be stored
202 * @see av_hash_final_bin() provides an alternative API
204 void av_hash_final(struct AVHashContext *ctx, uint8_t *dst);
207 * Finalize a hash context and store the actual hash value in a buffer.
209 * It is not safe to update or finalize a hash context again, if it has already
212 * If `size` is smaller than the hash size (given by av_hash_get_size()), the
213 * hash is truncated; if size is larger, the buffer is padded with 0.
215 * @param[in,out] ctx Hash context
216 * @param[out] dst Where the final hash value will be stored
217 * @param[in] size Number of bytes to write to `dst`
219 void av_hash_final_bin(struct AVHashContext *ctx, uint8_t *dst, int size);
222 * Finalize a hash context and store the hexadecimal representation of the
223 * actual hash value as a string.
225 * It is not safe to update or finalize a hash context again, if it has already
228 * The string is always 0-terminated.
230 * If `size` is smaller than `2 * hash_size + 1`, where `hash_size` is the
231 * value returned by av_hash_get_size(), the string will be truncated.
233 * @param[in,out] ctx Hash context
234 * @param[out] dst Where the string will be stored
235 * @param[in] size Maximum number of bytes to write to `dst`
237 void av_hash_final_hex(struct AVHashContext *ctx, uint8_t *dst, int size);
240 * Finalize a hash context and store the Base64 representation of the
241 * actual hash value as a string.
243 * It is not safe to update or finalize a hash context again, if it has already
246 * The string is always 0-terminated.
248 * If `size` is smaller than AV_BASE64_SIZE(hash_size), where `hash_size` is
249 * the value returned by av_hash_get_size(), the string will be truncated.
251 * @param[in,out] ctx Hash context
252 * @param[out] dst Where the final hash value will be stored
253 * @param[in] size Maximum number of bytes to write to `dst`
255 void av_hash_final_b64(struct AVHashContext *ctx, uint8_t *dst, int size);
258 * Free hash context and set hash context pointer to `NULL`.
260 * @param[in,out] ctx Pointer to hash context
262 void av_hash_freep(struct AVHashContext **ctx);
269 #endif /* AVUTIL_HASH_H */