src/cx/hash_key.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:
 *
 *   1. Redistributions of source code must retain the above copyright
 *      notice, this list of conditions and the following disclaimer.
 *
 *   2. Redistributions in binary form must reproduce the above copyright
 *      notice, this list of conditions and the following disclaimer in the
 *      documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */
/**
 * @file hash_key.h
 * @brief Interface for map implementations.
 * @author Mike Becker
 * @author Olaf Wintermann
 * @copyright 2-Clause BSD License
 */


#ifndef UCX_HASH_KEY_H
#define UCX_HASH_KEY_H

#include "common.h"
#include "string.h"

#ifdef __cplusplus
extern "C" {
#endif

/** Internal structure for a key within a hash map. */
struct cx_hash_key_s {
    /**
     * The key data.
     * May be NULL when the hash is collision-free.
     */
    const void *data;
    /**
     * The key data length.
     */
    size_t len;
    /** The hash value of the key data. */
    uint64_t hash;
};

/**
 * Type for a hash key.
 */
typedef struct cx_hash_key_s CxHashKey;

/**
 * Computes a murmur2 32-bit hash.
 *
 * You need to initialize @c data and @c len in the key struct.
 * The hash is then directly written to that struct.
 *
 * Usually you should not need this function.
 * Use cx_hash_key(), instead.
 *
 * @note If @c data is @c NULL, the hash is defined as 1574210520.
 *
 * @param key the key, the hash shall be computed for
 * @see cx_hash_key()
 */
cx_attr_nonnull
cx_attr_export
void cx_hash_murmur(CxHashKey *key);

/**
 * Mixes up a 32-bit integer to be used as a hash.
 *
 * This function produces no collisions and has a good statistical distribution.
 *
 * @param x the integer
 * @return the hash
 */
cx_attr_export
uint32_t cx_hash_u32(uint32_t x);

/**
 * Mixes up a 64-bit integer to be used as a hash.
 *
 * This function produces no collisions and has a good statistical distribution.
 *
 * @param x the integer
 * @return the hash
 */
cx_attr_export
uint64_t cx_hash_u64(uint64_t x);

/**
 * Computes a hash key from a 32-bit integer.
 *
 * @param x the integer
 * @return the hash key
 */
cx_attr_nodiscard
cx_attr_export
CxHashKey cx_hash_key_u32(uint32_t x);

/**
 * Computes a hash key from a 64-bit integer.
 *
 * @param x the integer
 * @return the hash key
 */
cx_attr_nodiscard
cx_attr_export
CxHashKey cx_hash_key_u64(uint64_t x);

/**
 * Computes a hash key from a string.
 *
 * The string needs to be zero-terminated.
 *
 * @param str the string
 * @return the hash key
 */
cx_attr_nodiscard
cx_attr_cstr_arg(1)
cx_attr_export
CxHashKey cx_hash_key_str(const char *str);

/**
 * Computes a hash key from a byte array.
 *
 * @param bytes the array
 * @param len the length
 * @return the hash key
 */
cx_attr_nodiscard
cx_attr_access_r(1, 2)
cx_attr_export
CxHashKey cx_hash_key_bytes(
        const unsigned char *bytes,
        size_t len
);

/**
 * Computes a hash key for an arbitrary object.
 *
 * The computation uses the in-memory representation that might not be
 * the same on different platforms. Therefore, this hash should not be
 * used for data exchange with different machines.
 *
 * @param obj a pointer to an arbitrary object
 * @param len the length of object in memory
 * @return the hash key
 */
cx_attr_nodiscard
cx_attr_access_r(1, 2)
cx_attr_export
CxHashKey cx_hash_key(
        const void *obj,
        size_t len
);

/**
 * Computes a hash key from a UCX string.
 *
 * @param str the string
 * @return the hash key
 */
cx_attr_nodiscard
static inline CxHashKey cx_hash_key_cxstr(cxstring str) {
    return cx_hash_key(str.ptr, str.length);
}

/**
 * Computes a hash key from a UCX string.
 *
 * @param str (@c cxstring or @c cxmutstr) the string
 * @return (@c CxHashKey) the hash key
 */
#define cx_hash_key_cxstr(str) cx_hash_key_cxstr(cx_strcast(str))

/**
 * Compare function for hash keys.
 *
 * @param left the first key
 * @param right the second key
 * @return zero when the keys equal, non-zero when they differ
 */
cx_attr_nodiscard
cx_attr_nonnull
cx_attr_export
int cx_hash_key_cmp(const CxHashKey *left, const CxHashKey *right);

#ifdef __cplusplus
} // extern "C"
#endif

#endif // UCX_HASH_KEY_H