/*
 * Copyright (C) 2018 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef TNT_UTILS_HASH_H
#define TNT_UTILS_HASH_H

#include <stdint.h>
#include <stddef.h>

namespace utils {
namespace hash {

inline uint32_t murmur3(const uint32_t* key, size_t wordCount, uint32_t seed) {
    uint32_t h = seed;
    size_t i = wordCount;
    do {
        uint32_t k = *key++;
        k *= 0xcc9e2d51;
        k = (k << 15) | (k >> 17);
        k *= 0x1b873593;
        h ^= k;
        h = (h << 13) | (h >> 19);
        h = (h * 5) + 0xe6546b64;
    } while (--i);
    h ^= wordCount;
    h ^= h >> 16;
    h *= 0x85ebca6b;
    h ^= h >> 13;
    h *= 0xc2b2ae35;
    h ^= h >> 16;
    return h;
}

template<typename T>
struct MurmurHashFn {
    uint32_t operator()(const T& key) const {
        static_assert(0 == (sizeof(key) & 3), "Hashing requires a size that is a multiple of 4.");
        return murmur3((const uint32_t*) &key, sizeof(key) / 4, 0);
    }
};

} // namespace hash
} // namespace utils

#endif // TNT_UTILS_HASH_H