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
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 */
/**
 * @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"

/** 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_EXTERN CX_NONNULL
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_INLINE
uint32_t cx_hash_u32(uint32_t x) {
    x = ((x >> 16) ^ x) * 0x45d9f3bu;
    x = ((x >> 16) ^ x) * 0x45d9f3bu;
    x = (x >> 16) ^ x;
    return 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_INLINE
uint64_t cx_hash_u64(uint64_t x){
    x = (x ^ (x >> 30)) * UINT64_C(0xbf58476d1ce4e5b9);
    x = (x ^ (x >> 27)) * UINT64_C(0x94d049bb133111eb);
    x = x ^ (x >> 31);
    return x;
}

/**
 * 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 the object in memory
 * @return the hash key
 */
CX_EXTERN CX_NODISCARD CX_ACCESS_R(1, 2)
CxHashKey cx_hash_key(const void *obj, size_t len);

/**
 * Computes a hash key from a 32-bit integer.
 *
 * @param x the integer
 * @return the hash key
 */
CX_NODISCARD CX_INLINE
CxHashKey cx_hash_key_u32(uint32_t x) {
    CxHashKey key;
    key.data = NULL;
    key.len = 0;
    key.hash = cx_hash_u32(x);
    return key;
}

/**
 * Computes a hash key from a 64-bit integer.
 *
 * @param x the integer
 * @return the hash key
 */
CX_NODISCARD CX_INLINE
CxHashKey cx_hash_key_u64(uint64_t x) {
    CxHashKey key;
    key.data = NULL;
    key.len = 0;
    key.hash = cx_hash_u64(x);
    return key;
}

/**
 * Computes a hash key from a string.
 *
 * The string needs to be zero-terminated.
 *
 * @param str the string
 * @return the hash key
 */
CX_NODISCARD CX_CSTR_ARG(1) CX_INLINE
CxHashKey cx_hash_key_str(const char *str) {
    return cx_hash_key((const void*)str, str == NULL ? 0 : strlen(str));
}

/**
 * Computes a hash key from a string.
 *
 * Use this function when the string is represented
 * as an unsigned char array.
 *
 * The string needs to be zero-terminated.
 *
 * @param str the string
 * @return the hash key
 */
CX_NODISCARD CX_CSTR_ARG(1) CX_INLINE
CxHashKey cx_hash_key_ustr(const unsigned char *str) {
    return cx_hash_key((const void*)str, str == NULL ? 0 : strlen((const char*)str));
}

/**
 * Computes a hash key from a byte array.
 *
 * @param bytes the array
 * @param len the length
 * @return the hash key
 */
CX_NODISCARD CX_ACCESS_R(1, 2) CX_INLINE
CxHashKey cx_hash_key_bytes(const unsigned char *bytes, size_t len) {
    return cx_hash_key((const void*)bytes, len);
}

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

/**
 * Computes a hash key from a UCX string.
 *
 * @param str the string
 * @return the hash key
 */
CX_NODISCARD CX_INLINE
CxHashKey cx_hash_key_mutstr(cxmutstr str) {
    return cx_hash_key((void*)str.ptr, str.length);
}

/**
 * The identity function for the CX_HASH_KEY() macro.
 * You should never need to use this manually.
 *
 * @param key the key
 * @return a copy of the key (not the data)
 */
CX_NODISCARD CX_INLINE
CxHashKey cx_hash_key_identity(CxHashKey key) {
    return key;
}

/**
 * The dereference function for the CX_HASH_KEY() macro.
 * You should never need to use this manually.
 *
 * @param key a pointer to a key
 * @return a copy of the key (not the data)
 */
CX_NODISCARD CX_INLINE
CxHashKey cx_hash_key_deref(const CxHashKey *key) {
    return *key;
}

#ifndef __cplusplus
/**
 * Creates a hash key from any of the supported types with implicit length.
 *
 * Does nothing when passing a CxHashKey and dereferences CxHashKey pointers.
 *
 * Supported types are UCX strings, zero-terminated C strings,
 * and 32-bit or 64-bit unsigned integers.
 *
 * @param key the key data
 * @returns the @c CxHashKey
 */
#define CX_HASH_KEY(key) _Generic((key), \
        CxHashKey*: cx_hash_key_deref, \
        const CxHashKey*: cx_hash_key_deref, \
        CxHashKey: cx_hash_key_identity, \
        cxstring: cx_hash_key_cxstr, \
        cxmutstr: cx_hash_key_mutstr, \
        char*: cx_hash_key_str, \
        const char*: cx_hash_key_str, \
        unsigned char*: cx_hash_key_ustr, \
        const unsigned char*: cx_hash_key_ustr, \
        uint32_t: cx_hash_key_u32, \
        uint64_t: cx_hash_key_u64) \
        (key)
#endif // __cplusplus

/**
 * Compare function for hash keys.
 *
 * The pointers are untyped to be compatible with the cx_compare_func signature.
 *
 * @param left (@c CxHashKey*) the first key
 * @param right (@c CxHashKey*) the second key
 * @return zero when the keys equal, non-zero when they differ
 */
CX_EXTERN CX_NODISCARD CX_NONNULL
int cx_hash_key_cmp(const void *left, const void *right);

/**
 * Interprets the key data as a string and returns it.
 *
 * @param key the key
 * @return the key data as a string
 */
CX_EXTERN
cxstring cx_hash_key_as_string(const CxHashKey *key);

#ifdef __cplusplus
// ----------------------------------------------------------
// Overloads of CX_HASH_KEY (the C++ version of a _Generic)
// ----------------------------------------------------------

CX_CPPDECL CxHashKey CX_HASH_KEY(CxHashKey key) {
    return key;
}

CX_CPPDECL CxHashKey CX_HASH_KEY(const CxHashKey *key) {
    return *key;
}

CX_CPPDECL CxHashKey CX_HASH_KEY(cxstring str) {
    return cx_hash_key_cxstr(str);
}

CX_CPPDECL CxHashKey CX_HASH_KEY(cxmutstr str) {
    return cx_hash_key_mutstr(str);
}

CX_CPPDECL CxHashKey CX_HASH_KEY(const char *str) {
    return cx_hash_key_str(str);
}

CX_CPPDECL CxHashKey CX_HASH_KEY(const unsigned char *str) {
    return cx_hash_key_ustr(str);
}

CX_CPPDECL CxHashKey CX_HASH_KEY(uint32_t key) {
    return cx_hash_key_u32(key);
}

CX_CPPDECL CxHashKey CX_HASH_KEY(uint64_t key) {
    return cx_hash_key_u64(key);
}
#endif

#endif // UCX_HASH_KEY_H