avutil/hash: Add more detailed Doxygen documentation

doc/Doxyfile

@@ -822,7 +822,7 @@ EXCLUDE_SYMBOLS        =
 # that contain example code fragments that are included (see the \include
 # command).
 
-EXAMPLE_PATH           = doc/examples/
+EXAMPLE_PATH           = doc/examples/ tools/
 
 # If the value of the EXAMPLE_PATH tag contains directories, you can use the
 # EXAMPLE_PATTERNS tag to specify one or more wildcard pattern (like *.cpp and

libavutil/hash.h

@@ -32,21 +32,94 @@
 /**
  * @defgroup lavu_hash Hash Functions
  * @ingroup lavu_crypto
+ * Hash functions useful in multimedia.
+ *
+ * Hash functions are widely used in multimedia, from error checking and
+ * concealment to internal regression testing. libavutil has efficient
+ * implementations of a variety of hash functions that may be useful for
+ * FFmpeg and other multimedia applications.
  *
  * @{
  *
  * @defgroup lavu_hash_generic Generic Hashing API
+ * An abstraction layer for all hash functions supported by libavutil.
+ *
+ * If your application needs to support a wide range of different hash
+ * functions, then the Generic Hashing API is for you. It provides a generic,
+ * reusable API for @ref lavu_hash "all hash functions" implemented in libavutil.
+ * If you just need to use one particular hash function, use the @ref lavu_hash
+ * "individual hash" directly.
+ *
+ * @section Sample Code
+ *
+ * A basic template for using the Generic Hashing API follows:
+ *
+ * @code
+ * struct AVHashContext *ctx = NULL;
+ * const char *hash_name = NULL;
+ * uint8_t *output_buf = NULL;
+ *
+ * // Select from a string returned by av_hash_names()
+ * hash_name = ...;
+ *
+ * // Allocate a hash context
+ * ret = av_hash_alloc(&ctx, hash_name);
+ * if (ret < 0)
+ *     return ret;
+ *
+ * // Initialize the hash context
+ * av_hash_init(ctx);
+ *
+ * // Update the hash context with data
+ * while (data_left) {
+ *     av_hash_update(ctx, data, size);
+ * }
+ *
+ * // Now we have no more data, so it is time to finalize the hash and get the
+ * // output. But we need to first allocate an output buffer. Note that you can
+ * // use any memory allocation function, including malloc(), not just
+ * // av_malloc().
+ * output_buf = av_malloc(av_hash_get_size(ctx));
+ * if (!output_buf)
+ *     return AVERROR(ENOMEM);
+ *
+ * // Finalize the hash context.
+ * // You can use any of the av_hash_final*() functions provided, for other
+ * // output formats. If you do so, be sure to adjust the memory allocation
+ * // above. See the function documentation below for the exact amount of extra
+ * // memory needed.
+ * av_hash_final(ctx, output_buffer);
+ *
+ * // Free the context
+ * av_hash_freep(&ctx);
+ * @endcode
+ *
+ * @section Hash Function-Specific Information
+ * If the CRC32 hash is selected, the #AV_CRC_32_IEEE polynomial will be
+ * used.
+ *
+ * If the Murmur3 hash is selected, the default seed will be used. See @ref
+ * lavu_murmur3_seedinfo "Murmur3" for more information.
  *
  * @{
  */
 
+/**
+ * @example ffhash.c
+ * This example is a simple command line application that takes one or more
+ * arguments. It demonstrates a typical use of the hashing API with allocation,
+ * initialization, updating, and finalizing.
+ */
+
 struct AVHashContext;
 
 /**
  * Allocate a hash context for the algorithm specified by name.
  *
  * @return  >= 0 for success, a negative error code for failure
- * @note  The context is not initialized, you must call av_hash_init().
+ *
+ * @note The context is not initialized after a call to this function; you must
+ * call av_hash_init() to do so.
  */
 int av_hash_alloc(struct AVHashContext **ctx, const char *name);
 
@@ -55,8 +128,8 @@ int av_hash_alloc(struct AVHashContext **ctx, const char *name);
  *
  * This function can be used to enumerate the algorithms.
  *
- * @param i  index of the hash algorithm, starting from 0
+ * @param[in] i  Index of the hash algorithm, starting from 0
- * @return   a pointer to a static string or NULL if i is out of range
+ * @return       Pointer to a static string or `NULL` if `i` is out of range
  */
 const char *av_hash_names(int i);
 
@@ -66,63 +139,119 @@ const char *av_hash_names(int i);
 const char *av_hash_get_name(const struct AVHashContext *ctx);
 
 /**
- * Maximum value that av_hash_get_size will currently return.
+ * Maximum value that av_hash_get_size() will currently return.
  *
- * You can use this if you absolutely want or need to use static allocation
+ * You can use this if you absolutely want or need to use static allocation for
- * and are fine with not supporting hashes newly added to libavutil without
+ * the output buffer and are fine with not supporting hashes newly added to
- * recompilation.
+ * libavutil without recompilation.
- * Note that you still need to check against av_hash_get_size, adding new hashes
+ *
- * with larger sizes will not be considered an ABI change and should not cause
+ * @warning
- * your code to overflow a buffer.
+ * Adding new hashes with larger sizes, and increasing the macro while doing
+ * so, will not be considered an ABI change. To prevent your code from
+ * overflowing a buffer, either dynamically allocate the output buffer with
+ * av_hash_get_size(), or limit your use of the Hashing API to hashes that are
+ * already in FFmpeg during the time of compilation.
  */
 #define AV_HASH_MAX_SIZE 64
 
 /**
  * Get the size of the resulting hash value in bytes.
  *
- * The pointer passed to av_hash_final have space for at least this many bytes.
+ * The maximum value this function will currently return is available as macro
+ * #AV_HASH_MAX_SIZE.
+ *
+ * @param[in]     ctx Hash context
+ * @return            Size of the hash value in bytes
  */
 int av_hash_get_size(const struct AVHashContext *ctx);
 
 /**
  * Initialize or reset a hash context.
+ *
+ * @param[in,out] ctx Hash context
  */
 void av_hash_init(struct AVHashContext *ctx);
 
 /**
  * Update a hash context with additional data.
+ *
+ * @param[in,out] ctx Hash context
+ * @param[in]     src Data to be added to the hash context
+ * @param[in]     len Size of the additional data
  */
 void av_hash_update(struct AVHashContext *ctx, const uint8_t *src, int len);
 
 /**
  * Finalize a hash context and compute the actual hash value.
+ *
+ * The minimum size of `dst` buffer is given by av_hash_get_size() or
+ * #AV_HASH_MAX_SIZE. The use of the latter macro is discouraged.
+ *
+ * It is not safe to update or finalize a hash context again, if it has already
+ * been finalized.
+ *
+ * @param[in,out] ctx Hash context
+ * @param[out]    dst Where the final hash value will be stored
+ *
+ * @see av_hash_final_bin() provides an alternative API
  */
 void av_hash_final(struct AVHashContext *ctx, uint8_t *dst);
 
 /**
- * Finalize a hash context and compute the actual hash value.
+ * Finalize a hash context and store the actual hash value in a buffer.
- * If size is smaller than the hash size, the hash is truncated;
+ *
- * if size is larger, the buffer is padded with 0.
+ * It is not safe to update or finalize a hash context again, if it has already
+ * been finalized.
+ *
+ * If `size` is smaller than the hash size (given by av_hash_get_size()), the
+ * hash is truncated; if size is larger, the buffer is padded with 0.
+ *
+ * @param[in,out] ctx  Hash context
+ * @param[out]    dst  Where the final hash value will be stored
+ * @param[in]     size Number of bytes to write to `dst`
  */
 void av_hash_final_bin(struct AVHashContext *ctx, uint8_t *dst, int size);
 
 /**
- * Finalize a hash context and compute the actual hash value as a hex string.
+ * Finalize a hash context and store the hexadecimal representation of the
+ * actual hash value as a string.
+ *
+ * It is not safe to update or finalize a hash context again, if it has already
+ * been finalized.
+ *
  * The string is always 0-terminated.
- * If size is smaller than 2 * hash_size + 1, the hex string is truncated.
+ *
+ * If `size` is smaller than `2 * hash_size + 1`, where `hash_size` is the
+ * value returned by av_hash_get_size(), the string will be truncated.
+ *
+ * @param[in,out] ctx  Hash context
+ * @param[out]    dst  Where the string will be stored
+ * @param[in]     size Maximum number of bytes to write to `dst`
  */
 void av_hash_final_hex(struct AVHashContext *ctx, uint8_t *dst, int size);
 
 /**
- * Finalize a hash context and compute the actual hash value as a base64 string.
+ * Finalize a hash context and store the Base64 representation of the
+ * actual hash value as a string.
+ *
+ * It is not safe to update or finalize a hash context again, if it has already
+ * been finalized.
+ *
  * The string is always 0-terminated.
- * If size is smaller than AV_BASE64_SIZE(hash_size), the base64 string is
+ *
- * truncated.
+ * If `size` is smaller than AV_BASE64_SIZE(hash_size), where `hash_size` is
+ * the value returned by av_hash_get_size(), the string will be truncated.
+ *
+ * @param[in,out] ctx  Hash context
+ * @param[out]    dst  Where the final hash value will be stored
+ * @param[in]     size Maximum number of bytes to write to `dst`
  */
 void av_hash_final_b64(struct AVHashContext *ctx, uint8_t *dst, int size);
 
 /**
- * Free hash context.
+ * Free hash context and set hash context pointer to `NULL`.
+ *
+ * @param[in,out] ctx  Pointer to hash context
  */
 void av_hash_freep(struct AVHashContext **ctx);