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/*
 * Copyright (C) 2011 The Guava Authors
 *
 * 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.
 */

package com.google.common.hash;

import static com.google.common.primitives.UnsignedBytes.toInt;

import com.google.common.primitives.Chars;
import com.google.common.primitives.Ints;
import com.google.common.primitives.Longs;

import java.io.Serializable;
import java.nio.ByteBuffer;

/**
 * See http://smhasher.googlecode.com/svn/trunk/MurmurHash3.cpp
 * MurmurHash3_x86_32
 *
 * @author Austin Appleby
 * @author Dimitris Andreou
 * @author Kurt Alfred Kluever
 */
final class Murmur3_32HashFunction extends AbstractStreamingHashFunction implements Serializable {
  private static final int C1 = 0xcc9e2d51;
  private static final int C2 = 0x1b873593;

  private final int seed;

  Murmur3_32HashFunction(int seed) {
    this.seed = seed;
  }

  @Override public int bits() {
    return 32;
  }

  @Override public Hasher newHasher() {
    return new Murmur3_32Hasher(seed);
  }

  @Override public HashCode hashInt(int input) {
    int k1 = mixK1(input);
    int h1 = mixH1(seed, k1);

    return fmix(h1, Ints.BYTES);
  }

  @Override public HashCode hashLong(long input) {
    int low = (int) input;
    int high = (int) (input >>> 32);

    int k1 = mixK1(low);
    int h1 = mixH1(seed, k1);

    k1 = mixK1(high);
    h1 = mixH1(h1, k1);

    return fmix(h1, Longs.BYTES);
  }

  // TODO(user): Maybe implement #hashBytes instead?
  @Override public HashCode hashString(CharSequence input) {
    int h1 = seed;

    // step through the CharSequence 2 chars at a time
    for (int i = 1; i < input.length(); i += 2) {
      int k1 = input.charAt(i - 1) | (input.charAt(i) << 16);
      k1 = mixK1(k1);
      h1 = mixH1(h1, k1);
    }

    // deal with any remaining characters
    if ((input.length() & 1) == 1) {
      int k1 = input.charAt(input.length() - 1);
      k1 = mixK1(k1);
      h1 ^= k1;
    }

    return fmix(h1, Chars.BYTES * input.length());
  }

  private static int mixK1(int k1) {
    k1 *= C1;
    k1 = Integer.rotateLeft(k1, 15);
    k1 *= C2;
    return k1;
  }

  private static int mixH1(int h1, int k1) {
    h1 ^= k1;
    h1 = Integer.rotateLeft(h1, 13);
    h1 = h1 * 5 + 0xe6546b64;
    return h1;
  }

  // Finalization mix - force all bits of a hash block to avalanche
  private static HashCode fmix(int h1, int length) {
    h1 ^= length;
    h1 ^= h1 >>> 16;
    h1 *= 0x85ebca6b;
    h1 ^= h1 >>> 13;
    h1 *= 0xc2b2ae35;
    h1 ^= h1 >>> 16;
    return HashCodes.fromInt(h1);
  }

  private static final class Murmur3_32Hasher extends AbstractStreamingHasher {
    private static final int CHUNK_SIZE = 4;
    private int h1;
    private int length;

    Murmur3_32Hasher(int seed) {
      super(CHUNK_SIZE);
      this.h1 = seed;
      this.length = 0;
    }

    @Override protected void process(ByteBuffer bb) {
      int k1 = Murmur3_32HashFunction.mixK1(bb.getInt());
      h1 = Murmur3_32HashFunction.mixH1(h1, k1);
      length += CHUNK_SIZE;
    }

    @Override protected void processRemaining(ByteBuffer bb) {
      length += bb.remaining();
      int k1 = 0;
      switch (bb.remaining()) {
        case 3:
          k1 ^= toInt(bb.get(2)) << 16; // fall through
        case 2:
          k1 ^= toInt(bb.get(1)) << 8; // fall through
        case 1:
          k1 ^= toInt(bb.get(0));
          break;
        default:
          throw new AssertionError("Should never get here.");
      }
      h1 ^= Murmur3_32HashFunction.mixK1(k1);
    }

    @Override public HashCode makeHash() {
      return Murmur3_32HashFunction.fmix(h1, length);
    }
  }

  private static final long serialVersionUID = 0L;
}