ucx/cx/hash_map.h

/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright 2021 Mike Becker, Olaf Wintermann All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
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 *      notice, this list of conditions and the following disclaimer.
 *
 *   2. Redistributions in binary form must reproduce the above copyright
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/**
 * @file hash_map.h
 * @brief Hash map implementation.
 * @author Mike Becker
 * @author Olaf Wintermann
 * @copyright 2-Clause BSD License
 */

#ifndef UCX_HASH_MAP_H
#define UCX_HASH_MAP_H

#include "map.h"

/** Internal structure for an element of a hash map. */
struct cx_hash_map_element_s;

/**
 * Internal structure for a hash map.
 */
struct cx_hash_map_s {
    /**
     * Base structure for maps.
     */
    struct cx_map_s base;
    /**
     * The buckets of this map, each containing a linked list of elements.
     */
    struct cx_hash_map_element_s **buckets;
    /**
     * The number of buckets.
     */
    size_t bucket_count;
};


/**
 * Creates a new hash map with the specified number of buckets.
 *
 * If @p buckets is zero, an implementation defined default will be used.
 *
 * If @p elem_size is #CX_STORE_POINTERS, the created map stores pointers instead of
 * copies of the added elements.
 *
 * @note Iterators provided by this hash map implementation provide the remove operation.
 * The index value of an iterator is incremented when the iterator advanced without
 * removing an entry.
 * In other words, when the iterator is finished, @c index==size .
 *
 * @param allocator the allocator to use
 * (if @c NULL, the cxDefaultAllocator will be used)
 * @param itemsize the size of one element
 * @param buckets the initial number of buckets in this hash map
 * @return a pointer to the new hash map
 */
CX_EXTERN CX_NODISCARD CX_MALLOC CX_DEALLOC(cxMapFree, 1)
CxMap *cxHashMapCreate(const CxAllocator *allocator,
        size_t itemsize, size_t buckets);

/**
 * Increases the number of buckets, if necessary.
 *
 * The load threshold is @c 0.75*buckets. If the element count exceeds the load
 * threshold, the map will be rehashed. Otherwise, no action is performed, and
 * this function simply returns 0.
 *
 * The rehashing process ensures that the number of buckets is at least
 * 2.5 times the element count. So there is enough room for additional
 * elements without the need of another soon rehashing.
 *
 * You can use this function after filling a map to increase access performance.
 *
 * @note If the specified map is not a hash map, the behavior is undefined.
 *
 * @param map the map to rehash
 * @retval zero success
 * @retval non-zero if a memory allocation error occurred
 */
CX_EXTERN CX_NONNULL
int cxMapRehash(CxMap *map);

#endif // UCX_HASH_MAP_H