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      1 /*
      2  * Copyright (C) 2011 The Guava Authors
      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 package com.google.common.hash;
     18 
     19 import com.google.common.base.Preconditions;
     20 
     21 import java.io.ByteArrayOutputStream;
     22 import java.io.IOException;
     23 import java.nio.charset.Charset;
     24 
     25 /**
     26  * Skeleton implementation of {@link HashFunction}, appropriate for non-streaming algorithms.
     27  * All the hash computation done using {@linkplain #newHasher()} are delegated to the {@linkplain
     28  * #hashBytes(byte[], int, int)} method.
     29  *
     30  * @author Dimitris Andreou
     31  */
     32 abstract class AbstractNonStreamingHashFunction implements HashFunction {
     33   @Override
     34   public Hasher newHasher() {
     35     return new BufferingHasher(32);
     36   }
     37 
     38   @Override
     39   public Hasher newHasher(int expectedInputSize) {
     40     Preconditions.checkArgument(expectedInputSize >= 0);
     41     return new BufferingHasher(expectedInputSize);
     42   }
     43 
     44   @Override public <T> HashCode hashObject(T instance, Funnel<? super T> funnel) {
     45     return newHasher().putObject(instance, funnel).hash();
     46   }
     47 
     48   @Override public HashCode hashUnencodedChars(CharSequence input) {
     49     int len = input.length();
     50     Hasher hasher = newHasher(len * 2);
     51     for (int i = 0; i < len; i++) {
     52       hasher.putChar(input.charAt(i));
     53     }
     54     return hasher.hash();
     55   }
     56 
     57   @Override public HashCode hashString(CharSequence input, Charset charset) {
     58     return hashBytes(input.toString().getBytes(charset));
     59   }
     60 
     61   @Override public HashCode hashInt(int input) {
     62     return newHasher(4).putInt(input).hash();
     63   }
     64 
     65   @Override public HashCode hashLong(long input) {
     66     return newHasher(8).putLong(input).hash();
     67   }
     68 
     69   @Override public HashCode hashBytes(byte[] input) {
     70     return hashBytes(input, 0, input.length);
     71   }
     72 
     73   /**
     74    * In-memory stream-based implementation of Hasher.
     75    */
     76   private final class BufferingHasher extends AbstractHasher {
     77     final ExposedByteArrayOutputStream stream;
     78     static final int BOTTOM_BYTE = 0xFF;
     79 
     80     BufferingHasher(int expectedInputSize) {
     81       this.stream = new ExposedByteArrayOutputStream(expectedInputSize);
     82     }
     83 
     84     @Override
     85     public Hasher putByte(byte b) {
     86       stream.write(b);
     87       return this;
     88     }
     89 
     90     @Override
     91     public Hasher putBytes(byte[] bytes) {
     92       try {
     93         stream.write(bytes);
     94       } catch (IOException e) {
     95         throw new RuntimeException(e);
     96       }
     97       return this;
     98     }
     99 
    100     @Override
    101     public Hasher putBytes(byte[] bytes, int off, int len) {
    102       stream.write(bytes, off, len);
    103       return this;
    104     }
    105 
    106     @Override
    107     public Hasher putShort(short s) {
    108       stream.write(s & BOTTOM_BYTE);
    109       stream.write((s >>> 8)  & BOTTOM_BYTE);
    110       return this;
    111     }
    112 
    113     @Override
    114     public Hasher putInt(int i) {
    115       stream.write(i & BOTTOM_BYTE);
    116       stream.write((i >>> 8) & BOTTOM_BYTE);
    117       stream.write((i >>> 16) & BOTTOM_BYTE);
    118       stream.write((i >>> 24) & BOTTOM_BYTE);
    119       return this;
    120     }
    121 
    122     @Override
    123     public Hasher putLong(long l) {
    124       for (int i = 0; i < 64; i += 8) {
    125         stream.write((byte) ((l >>> i) & BOTTOM_BYTE));
    126       }
    127       return this;
    128     }
    129 
    130     @Override
    131     public Hasher putChar(char c) {
    132       stream.write(c & BOTTOM_BYTE);
    133       stream.write((c >>> 8) & BOTTOM_BYTE);
    134       return this;
    135     }
    136 
    137     @Override
    138     public <T> Hasher putObject(T instance, Funnel<? super T> funnel) {
    139       funnel.funnel(instance, this);
    140       return this;
    141     }
    142 
    143     @Override
    144     public HashCode hash() {
    145       return hashBytes(stream.byteArray(), 0, stream.length());
    146     }
    147   }
    148 
    149   // Just to access the byte[] without introducing an unnecessary copy
    150   private static final class ExposedByteArrayOutputStream extends ByteArrayOutputStream {
    151     ExposedByteArrayOutputStream(int expectedInputSize) {
    152       super(expectedInputSize);
    153     }
    154     byte[] byteArray() {
    155       return buf;
    156     }
    157     int length() {
    158       return count;
    159     }
    160   }
    161 }
    162