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      1 /*
      2  * Copyright (C) 2012 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 /* Implementation of Jenkins one-at-a-time hash function. These choices are
     18  * optimized for code size and portability, rather than raw speed. But speed
     19  * should still be quite good.
     20  **/
     21 
     22 #include <utils/JenkinsHash.h>
     23 
     24 namespace android {
     25 
     26 hash_t JenkinsHashWhiten(uint32_t hash) {
     27     hash += (hash << 3);
     28     hash ^= (hash >> 11);
     29     hash += (hash << 15);
     30     return hash;
     31 }
     32 
     33 uint32_t JenkinsHashMixBytes(uint32_t hash, const uint8_t* bytes, size_t size) {
     34     hash = JenkinsHashMix(hash, (uint32_t)size);
     35     size_t i;
     36     for (i = 0; i < (size & -4); i += 4) {
     37         uint32_t data = bytes[i] | (bytes[i+1] << 8) | (bytes[i+2] << 16) | (bytes[i+3] << 24);
     38         hash = JenkinsHashMix(hash, data);
     39     }
     40     if (size & 3) {
     41         uint32_t data = bytes[i];
     42         data |= ((size & 3) > 1) ? (bytes[i+1] << 8) : 0;
     43         data |= ((size & 3) > 2) ? (bytes[i+2] << 16) : 0;
     44         hash = JenkinsHashMix(hash, data);
     45     }
     46     return hash;
     47 }
     48 
     49 uint32_t JenkinsHashMixShorts(uint32_t hash, const uint16_t* shorts, size_t size) {
     50     hash = JenkinsHashMix(hash, (uint32_t)size);
     51     size_t i;
     52     for (i = 0; i < (size & -2); i += 2) {
     53         uint32_t data = shorts[i] | (shorts[i+1] << 16);
     54         hash = JenkinsHashMix(hash, data);
     55     }
     56     if (size & 1) {
     57         uint32_t data = shorts[i];
     58         hash = JenkinsHashMix(hash, data);
     59     }
     60     return hash;
     61 }
     62 
     63 }
     64 
     65