/*      $NetBSD: murmurhash.c,v 1.10 2026/01/03 17:09:57 nia Exp $      */

/*
 * MurmurHash2 -- from the original code:
 *
 * "MurmurHash2 was written by Austin Appleby, and is placed in the public
 * domain. The author hereby disclaims copyright to this source code."
 *
 * References:
 *      http://code.google.com/p/smhasher/
 *      https://sites.google.com/site/murmurhash/
 */

#include <sys/cdefs.h>

#if defined(_KERNEL) || defined(_STANDALONE)
__KERNEL_RCSID(0, "$NetBSD: murmurhash.c,v 1.10 2026/01/03 17:09:57 nia Exp $");

#include <lib/libkern/libkern.h>

#else

#if defined(LIBC_SCCS) && !defined(lint)
__RCSID("$NetBSD: murmurhash.c,v 1.10 2026/01/03 17:09:57 nia Exp $");
#endif /* LIBC_SCCS and not lint */

#include "namespace.h"
#include <string.h>

#endif

#include <sys/types.h>
#include <sys/param.h>
#include <sys/endian.h>
#include <sys/hash.h>

#if !defined(_KERNEL) && !defined(_STANDALONE)
#ifdef __weak_alias
__weak_alias(murmurhash2,_murmurhash2)
#endif
#endif

uint32_t
murmurhash2(const void *key, size_t len, uint32_t seed)
{
        /*
         * Note: 'm' and 'r' are mixing constants generated offline.
         * They're not really 'magic', they just happen to work well.
         * Initialize the hash to a 'random' value.
         */
        const uint32_t m = 0x5bd1e995;
        const int r = 24;

        const uint8_t *data = key;
        uint32_t h = seed ^ (uint32_t)len;

        if (__predict_true(ALIGNED_POINTER(key, uint32_t))) {
                while (len >= sizeof(uint32_t)) {
                        uint32_t k;

                        ALIGNED_POINTER_LOAD(&k, data, uint32_t);
                        k = htole32(k);

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

                        h *= m;
                        h ^= k;

                        data += sizeof(uint32_t);
                        len -= sizeof(uint32_t);
                }
        } else {
                while (len >= sizeof(uint32_t)) {
                        uint32_t k;

                        k  = data[0];
                        k |= data[1] << 8;
                        k |= data[2] << 16;
                        k |= (uint32_t)data[3] << 24;

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

                        h *= m;
                        h ^= k;

                        data += sizeof(uint32_t);
                        len -= sizeof(uint32_t);
                }
        }

        /* Handle the last few bytes of the input array. */
        switch (len) {
        case 3:
                h ^= data[2] << 16;
                /* FALLTHROUGH */
        case 2:
                h ^= data[1] << 8;
                /* FALLTHROUGH */
        case 1:
                h ^= data[0];
                h *= m;
        }

        /*
         * Do a few final mixes of the hash to ensure the last few
         * bytes are well-incorporated.
         */
        h ^= h >> 13;
        h *= m;
        h ^= h >> 15;

        return h;
}