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hash API
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========
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The hash API is a collection of simple hash table functions. Users are expected
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to implement their own hashing.
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Data Structures
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---------------
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`struct hash_table`::
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The hash table structure. The `array` member points to the hash table
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entries. The `size` member counts the total number of valid and invalid
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entries in the table. The `nr` member keeps track of the number of
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valid entries.
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`struct hash_table_entry`::
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An opaque structure representing an entry in the hash table. The `hash`
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member is the entry's hash key and the `ptr` member is the entry's
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value.
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Functions
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---------
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`init_hash`::
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Initialize the hash table.
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`free_hash`::
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Release memory associated with the hash table.
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`insert_hash`::
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Insert a pointer into the hash table. If an entry with that hash
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already exists, a pointer to the existing entry's value is returned.
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Otherwise NULL is returned. This allows callers to implement
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chaining, etc.
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`lookup_hash`::
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Lookup an entry in the hash table. If an entry with that hash exists
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the entry's value is returned. Otherwise NULL is returned.
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`for_each_hash`::
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Call a function for each entry in the hash table. The function is
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expected to take the entry's value as its only argument and return an
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int. If the function returns a negative int the loop is aborted
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immediately. Otherwise, the return value is accumulated and the sum
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returned upon completion of the loop.
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