src/hash_key.c

/*
 * 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.
 */

#include "cx/hash_key.h"
#include <string.h>

void cx_hash_murmur(CxHashKey *key) {
    unsigned char const *data = key->data.cbytes;
    if (data == NULL) {
        // extension: special value for NULL
        key->hash = 1574210520u;
        return;
    }
    size_t len = key->len;

    unsigned m = 0x5bd1e995;
    unsigned r = 24;
    unsigned h = 25 ^ len;
    unsigned i = 0;
    while (len >= 4) {
        unsigned k = data[i + 0] & 0xFF;
        k |= (data[i + 1] & 0xFF) << 8;
        k |= (data[i + 2] & 0xFF) << 16;
        k |= (data[i + 3] & 0xFF) << 24;

        k *= m;
        k ^= k >> r;
        k *= m;

        h *= m;
        h ^= k;

        i += 4;
        len -= 4;
    }

    switch (len) {
        case 3:
            h ^= (data[i + 2] & 0xFF) << 16;
                    __attribute__((__fallthrough__));
        case 2:
            h ^= (data[i + 1] & 0xFF) << 8;
                    __attribute__((__fallthrough__));
        case 1:
            h ^= (data[i + 0] & 0xFF);
            h *= m;
                    __attribute__((__fallthrough__));
        default: // do nothing
        ;
    }

    h ^= h >> 13;
    h *= m;
    h ^= h >> 15;

    key->hash = h;
}

CxHashKey cx_hash_key_str(char const *str) {
    CxHashKey key;
    key.data.cstr = str;
    key.len = str == NULL ? 0 : strlen(str);
    cx_hash_murmur(&key);
    return key;
}

CxHashKey cx_hash_key_bytes(
        unsigned char const *bytes,
        size_t len
) {
    CxHashKey key;
    key.data.cbytes = bytes;
    key.len = len;
    cx_hash_murmur(&key);
    return key;
}

CxHashKey cx_hash_key(
        void const *obj,
        size_t len
) {
    CxHashKey key;
    key.data.cobj = obj;
    key.len = len;
    cx_hash_murmur(&key);
    return key;
}