FFmpeg
hash.h
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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 */
name
it s the only field you need to keep assuming you have a context There is some magic you don t need to care about around this just let it vf default minimum maximum flags name is the option name
Definition: writing_filters.txt:88
av_hash_final_b64
void av_hash_final_b64(struct AVHashContext *ctx, uint8_t *dst, int size)
Finalize a hash context and store the Base64 representation of the actual hash value as a string.
Definition: hash.c:223
av_hash_get_name
const char * av_hash_get_name(const struct AVHashContext *ctx)
Get the name of the algorithm corresponding to the given hash context.
av_hash_final_bin
void av_hash_final_bin(struct AVHashContext *ctx, uint8_t *dst, int size)
Finalize a hash context and store the actual hash value in a buffer.
Definition: hash.c:202
av_hash_alloc
int av_hash_alloc(struct AVHashContext **ctx, const char *name)
Allocate a hash context for the algorithm specified by name.
Definition: hash.c:102
ctx
AVFormatContext * ctx
Definition: movenc.c:48
av_hash_names
const char * av_hash_names(int i)
Get the names of available hash algorithms.
Definition: hash.c:86
av_hash_init
void av_hash_init(struct AVHashContext *ctx)
Initialize or reset a hash context.
Definition: hash.c:139
src
#define src
Definition: vp8dsp.c:255
av_hash_get_size
int av_hash_get_size(const struct AVHashContext *ctx)
Get the size of the resulting hash value in bytes.
av_hash_update
void av_hash_update(struct AVHashContext *ctx, const uint8_t *src, size_t len)
Update a hash context with additional data.
Definition: hash.c:160
av_hash_freep
void av_hash_freep(struct AVHashContext **ctx)
Free hash context and set hash context pointer to NULL.
Definition: hash.c:236
size
int size
Definition: twinvq_data.h:10344
av_hash_final
void av_hash_final(struct AVHashContext *ctx, uint8_t *dst)
Finalize a hash context and compute the actual hash value.
Definition: hash.c:181
AVHashContext
Definition: hash.c:58
i
#define i(width, name, range_min, range_max)
Definition: cbs_h2645.c:271
len
int len
Definition: vorbis_enc_data.h:426
av_hash_final_hex
void av_hash_final_hex(struct AVHashContext *ctx, uint8_t *dst, int size)
Finalize a hash context and store the hexadecimal representation of the actual hash value as a string...
Definition: hash.c:213
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