liblzma: Improve documentation in index_hash.h.

All functions now explicitly specify parameter and return values.
Also reworded the description of lzma_index_hash_init() for readability.

src/liblzma/api/lzma/index_hash.h

@@ -29,13 +29,21 @@ typedef struct lzma_index_hash_s lzma_index_hash;
 /**
  * \brief       Allocate and initialize a new lzma_index_hash structure
  *
- * If index_hash is NULL, a new lzma_index_hash structure is allocated,
+ * If index_hash is NULL, this function allocates and initializes a new
- * initialized, and a pointer to it returned. If allocation fails, NULL
+ * lzma_index_hash structure and returns a pointer to it. If allocation
- * is returned.
+ * fails, NULL is returned.
  *
- * If index_hash is non-NULL, it is reinitialized and the same pointer
+ * If index_hash is non-NULL, this function reinitializes the lzma_index_hash
- * returned. In this case, return value cannot be NULL or a different
+ * structure and returns the same pointer. In this case, return value cannot
- * pointer than the index_hash that was given as an argument.
+ * be NULL or a different pointer than the index_hash that was given as
+ * an argument.
+ *
+ * \param       index_hash  Pointer to a lzma_index_hash structure or NULL.
+ * \param       allocator   lzma_allocator for custom allocator functions.
+ *                          Set to NULL to use malloc() and free().
+ *
+ * \return      Initialized lzma_index_hash structure on success or
+ *              NULL on failure.
  */
 extern LZMA_API(lzma_index_hash *) lzma_index_hash_init(
 		lzma_index_hash *index_hash, const lzma_allocator *allocator)
@@ -44,6 +52,10 @@ extern LZMA_API(lzma_index_hash *) lzma_index_hash_init(
 
 /**
  * \brief       Deallocate lzma_index_hash structure
+ *
+ * \param       index_hash  Pointer to a lzma_index_hash structure to free.
+ * \param       allocator   lzma_allocator for custom allocator functions.
+ *                          Set to NULL to use malloc() and free().
  */
 extern LZMA_API(void) lzma_index_hash_end(
 		lzma_index_hash *index_hash, const lzma_allocator *allocator)
@@ -57,7 +69,8 @@ extern LZMA_API(void) lzma_index_hash_end(
  * \param       unpadded_size     Unpadded Size of a Block
  * \param       uncompressed_size Uncompressed Size of a Block
  *
- * \return      - LZMA_OK
+ * \return      Possible lzma_ret values:
+ *              - LZMA_OK
  *              - LZMA_DATA_ERROR: Compressed or uncompressed size of the
  *                Stream or size of the Index field would grow too big.
  *              - LZMA_PROG_ERROR: Invalid arguments or this function is being
@@ -82,10 +95,11 @@ extern LZMA_API(lzma_ret) lzma_index_hash_append(lzma_index_hash *index_hash,
  *
  * \param       index_hash      Pointer to a lzma_index_hash structure
  * \param       in              Pointer to the beginning of the input buffer
- * \param       in_pos          in[*in_pos] is the next byte to process
+ * \param[out]  in_pos          in[*in_pos] is the next byte to process
  * \param       in_size         in[in_size] is the first byte not to process
  *
- * \return      - LZMA_OK: So far good, but more input is needed.
+ * \return      Possible lzma_ret values:
+ *              - LZMA_OK: So far good, but more input is needed.
  *              - LZMA_STREAM_END: Index decoded successfully and it matches
  *                the Records given with lzma_index_hash_append().
  *              - LZMA_DATA_ERROR: Index is corrupt or doesn't match the
@@ -102,6 +116,10 @@ extern LZMA_API(lzma_ret) lzma_index_hash_decode(lzma_index_hash *index_hash,
  * \brief       Get the size of the Index field as bytes
  *
  * This is needed to verify the Backward Size field in the Stream Footer.
+ *
+ * \param       index_hash      Pointer to a lzma_index_hash structure
+ * 
+ * \return      Size of the Index field in bytes.
  */
 extern LZMA_API(lzma_vli) lzma_index_hash_size(
 		const lzma_index_hash *index_hash)