libutils/JenkinsHash.cpp

/*
 * Copyright (C) 2012 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.
 */

/* Implementation of Jenkins one-at-a-time hash function. These choices are
 * optimized for code size and portability, rather than raw speed. But speed
 * should still be quite good.
 **/

#include <utils/JenkinsHash.h>

namespace android {

hash_t JenkinsHashWhiten(uint32_t hash) {
    hash += (hash << 3);
    hash ^= (hash >> 11);
    hash += (hash << 15);
    return hash;
}

uint32_t JenkinsHashMixBytes(uint32_t hash, const uint8_t* bytes, size_t size) {
    hash = JenkinsHashMix(hash, (uint32_t)size);
    size_t i;
    for (i = 0; i < (size & -4); i += 4) {
        uint32_t data = bytes[i] | (bytes[i+1] << 8) | (bytes[i+2] << 16) | (bytes[i+3] << 24);
        hash = JenkinsHashMix(hash, data);
    }
    if (size & 3) {
        uint32_t data = bytes[i];
        data |= ((size & 3) > 1) ? (bytes[i+1] << 8) : 0;
        data |= ((size & 3) > 2) ? (bytes[i+2] << 16) : 0;
        hash = JenkinsHashMix(hash, data);
    }
    return hash;
}

uint32_t JenkinsHashMixShorts(uint32_t hash, const uint16_t* shorts, size_t size) {
    hash = JenkinsHashMix(hash, (uint32_t)size);
    size_t i;
    for (i = 0; i < (size & -2); i += 2) {
        uint32_t data = shorts[i] | (shorts[i+1] << 16);
        hash = JenkinsHashMix(hash, data);
    }
    if (size & 1) {
        uint32_t data = shorts[i];
        hash = JenkinsHashMix(hash, data);
    }
    return hash;
}

}