001/*
002 * Copyright (C) 2011 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
005 * in compliance with the License. You may obtain a copy of the License at
006 *
007 * http://www.apache.org/licenses/LICENSE-2.0
008 *
009 * Unless required by applicable law or agreed to in writing, software distributed under the License
010 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
011 * or implied. See the License for the specific language governing permissions and limitations under
012 * the License.
013 */
014
015package com.google.common.hash;
016
017import static com.google.common.base.Preconditions.checkArgument;
018import static com.google.common.base.Preconditions.checkNotNull;
019import static com.google.common.base.Preconditions.checkState;
020
021import com.google.common.annotations.Beta;
022import com.google.common.base.Preconditions;
023import com.google.common.primitives.Ints;
024import com.google.common.primitives.UnsignedInts;
025
026import java.io.Serializable;
027import java.security.MessageDigest;
028
029import javax.annotation.Nullable;
030
031/**
032 * An immutable hash code of arbitrary bit length.
033 *
034 * @author Dimitris Andreou
035 * @author Kurt Alfred Kluever
036 * @since 11.0
037 */
038@Beta
039public abstract class HashCode {
040  HashCode() {}
041
042  /**
043   * Returns the number of bits in this hash code; a positive multiple of 8.
044   */
045  public abstract int bits();
046
047  /**
048   * Returns the first four bytes of {@linkplain #asBytes() this hashcode's bytes}, converted to
049   * an {@code int} value in little-endian order.
050   *
051   * @throws IllegalStateException if {@code bits() < 32}
052   */
053  public abstract int asInt();
054
055  /**
056   * Returns the first eight bytes of {@linkplain #asBytes() this hashcode's bytes}, converted to
057   * a {@code long} value in little-endian order.
058   *
059   * @throws IllegalStateException if {@code bits() < 64}
060   */
061  public abstract long asLong();
062
063  /**
064   * If this hashcode has enough bits, returns {@code asLong()}, otherwise returns a {@code long}
065   * value with {@code asBytes()} as the least-significant bytes and {@code 0x00} as the remaining
066   * most-significant bytes.
067   *
068   * @since 14.0 (since 11.0 as {@code Hashing.padToLong(HashCode)})
069   */
070  public abstract long padToLong();
071
072  /**
073   * Returns the value of this hash code as a byte array. The caller may modify the byte array;
074   * changes to it will <i>not</i> be reflected in this {@code HashCode} object or any other arrays
075   * returned by this method.
076   */
077  // TODO(user): consider ByteString here, when that is available
078  public abstract byte[] asBytes();
079
080  /**
081   * Copies bytes from this hash code into {@code dest}.
082   *
083   * @param dest the byte array into which the hash code will be written
084   * @param offset the start offset in the data
085   * @param maxLength the maximum number of bytes to write
086   * @return the number of bytes written to {@code dest}
087   * @throws IndexOutOfBoundsException if there is not enough room in {@code dest}
088   */
089  public int writeBytesTo(byte[] dest, int offset, int maxLength) {
090    maxLength = Ints.min(maxLength, bits() / 8);
091    Preconditions.checkPositionIndexes(offset, offset + maxLength, dest.length);
092    writeBytesToImpl(dest, offset, maxLength);
093    return maxLength;
094  }
095
096  abstract void writeBytesToImpl(byte[] dest, int offset, int maxLength);
097
098  /**
099   * Returns a mutable view of the underlying bytes for the given {@code HashCode} if it is a
100   * byte-based hashcode. Otherwise it returns {@link HashCode#asBytes}. Do <i>not</i> mutate this
101   * array or else you will break the immutability contract of {@code HashCode}.
102   */
103  byte[] getBytesInternal() {
104    return asBytes();
105  }
106
107  /**
108   * Creates a 32-bit {@code HashCode} representation of the given int value. The underlying bytes
109   * are interpreted in little endian order.
110   *
111   * @since 15.0 (since 12.0 in HashCodes)
112   */
113  public static HashCode fromInt(int hash) {
114    return new IntHashCode(hash);
115  }
116
117  private static final class IntHashCode extends HashCode implements Serializable {
118    final int hash;
119
120    IntHashCode(int hash) {
121      this.hash = hash;
122    }
123
124    @Override
125    public int bits() {
126      return 32;
127    }
128
129    @Override
130    public byte[] asBytes() {
131      return new byte[] {
132          (byte) hash,
133          (byte) (hash >> 8),
134          (byte) (hash >> 16),
135          (byte) (hash >> 24)};
136    }
137
138    @Override
139    public int asInt() {
140      return hash;
141    }
142
143    @Override
144    public long asLong() {
145      throw new IllegalStateException("this HashCode only has 32 bits; cannot create a long");
146    }
147
148    @Override
149    public long padToLong() {
150      return UnsignedInts.toLong(hash);
151    }
152
153    @Override
154    void writeBytesToImpl(byte[] dest, int offset, int maxLength) {
155      for (int i = 0; i < maxLength; i++) {
156        dest[offset + i] = (byte) (hash >> (i * 8));
157      }
158    }
159
160    private static final long serialVersionUID = 0;
161  }
162
163  /**
164   * Creates a 64-bit {@code HashCode} representation of the given long value. The underlying bytes
165   * are interpreted in little endian order.
166   *
167   * @since 15.0 (since 12.0 in HashCodes)
168   */
169  public static HashCode fromLong(long hash) {
170    return new LongHashCode(hash);
171  }
172
173  private static final class LongHashCode extends HashCode implements Serializable {
174    final long hash;
175
176    LongHashCode(long hash) {
177      this.hash = hash;
178    }
179
180    @Override
181    public int bits() {
182      return 64;
183    }
184
185    @Override
186    public byte[] asBytes() {
187      return new byte[] {
188          (byte) hash,
189          (byte) (hash >> 8),
190          (byte) (hash >> 16),
191          (byte) (hash >> 24),
192          (byte) (hash >> 32),
193          (byte) (hash >> 40),
194          (byte) (hash >> 48),
195          (byte) (hash >> 56)};
196    }
197
198    @Override
199    public int asInt() {
200      return (int) hash;
201    }
202
203    @Override
204    public long asLong() {
205      return hash;
206    }
207
208    @Override
209    public long padToLong() {
210      return hash;
211    }
212
213    @Override
214    void writeBytesToImpl(byte[] dest, int offset, int maxLength) {
215      for (int i = 0; i < maxLength; i++) {
216        dest[offset + i] = (byte) (hash >> (i * 8));
217      }
218    }
219
220    private static final long serialVersionUID = 0;
221  }
222
223  /**
224   * Creates a {@code HashCode} from a byte array. The array is defensively copied to preserve
225   * the immutability contract of {@code HashCode}. The array cannot be empty.
226   *
227   * @since 15.0 (since 12.0 in HashCodes)
228   */
229  public static HashCode fromBytes(byte[] bytes) {
230    checkArgument(bytes.length >= 1, "A HashCode must contain at least 1 byte.");
231    return fromBytesNoCopy(bytes.clone());
232  }
233
234  /**
235   * Creates a {@code HashCode} from a byte array. The array is <i>not</i> copied defensively,
236   * so it must be handed-off so as to preserve the immutability contract of {@code HashCode}.
237   */
238  static HashCode fromBytesNoCopy(byte[] bytes) {
239    return new BytesHashCode(bytes);
240  }
241
242  private static final class BytesHashCode extends HashCode implements Serializable {
243    final byte[] bytes;
244
245    BytesHashCode(byte[] bytes) {
246      this.bytes = checkNotNull(bytes);
247    }
248
249    @Override
250    public int bits() {
251      return bytes.length * 8;
252    }
253
254    @Override
255    public byte[] asBytes() {
256      return bytes.clone();
257    }
258
259    @Override
260    public int asInt() {
261      checkState(bytes.length >= 4,
262          "HashCode#asInt() requires >= 4 bytes (it only has %s bytes).", bytes.length);
263      return (bytes[0] & 0xFF)
264          | ((bytes[1] & 0xFF) << 8)
265          | ((bytes[2] & 0xFF) << 16)
266          | ((bytes[3] & 0xFF) << 24);
267    }
268
269    @Override
270    public long asLong() {
271      checkState(bytes.length >= 8,
272          "HashCode#asLong() requires >= 8 bytes (it only has %s bytes).", bytes.length);
273      return padToLong();
274    }
275
276    @Override
277    public long padToLong() {
278      long retVal = (bytes[0] & 0xFF);
279      for (int i = 1; i < Math.min(bytes.length, 8); i++) {
280        retVal |= (bytes[i] & 0xFFL) << (i * 8);
281      }
282      return retVal;
283    }
284
285    @Override
286    void writeBytesToImpl(byte[] dest, int offset, int maxLength) {
287      System.arraycopy(bytes, 0, dest, offset, maxLength);
288    }
289
290    @Override
291    byte[] getBytesInternal() {
292      return bytes;
293    }
294
295    private static final long serialVersionUID = 0;
296  }
297
298  /**
299   * Creates a {@code HashCode} from a hexadecimal ({@code base 16}) encoded string. The string must
300   * be at least 2 characters long, and contain only valid, lower-cased hexadecimal characters.
301   *
302   * <p>This method accepts the exact format generated by {@link #toString}. If you require more
303   * lenient {@code base 16} decoding, please use
304   * {@link com.google.common.io.BaseEncoding#decode} (and pass the result to {@link #fromBytes}).
305   *
306   * @since 15.0
307   */
308  public static HashCode fromString(String string) {
309    checkArgument(string.length() >= 2,
310        "input string (%s) must have at least 2 characters", string);
311    checkArgument(string.length() % 2 == 0,
312        "input string (%s) must have an even number of characters", string);
313
314    byte[] bytes = new byte[string.length() / 2];
315    for (int i = 0; i < string.length(); i += 2) {
316      int ch1 = decode(string.charAt(i)) << 4;
317      int ch2 = decode(string.charAt(i + 1));
318      bytes[i / 2] = (byte) (ch1 + ch2);
319    }
320    return fromBytesNoCopy(bytes);
321  }
322
323  private static int decode(char ch) {
324    if (ch >= '0' && ch <= '9') {
325      return ch - '0';
326    }
327    if (ch >= 'a' && ch <= 'f') {
328      return ch - 'a' + 10;
329    }
330    throw new IllegalArgumentException("Illegal hexadecimal character: " + ch);
331  }
332
333  @Override
334  public final boolean equals(@Nullable Object object) {
335    if (object instanceof HashCode) {
336      HashCode that = (HashCode) object;
337      // Undocumented: this is a non-short-circuiting equals(), in case this is a cryptographic
338      // hash code, in which case we don't want to leak timing information
339      return MessageDigest.isEqual(this.asBytes(), that.asBytes());
340    }
341    return false;
342  }
343
344  /**
345   * Returns a "Java hash code" for this {@code HashCode} instance; this is well-defined
346   * (so, for example, you can safely put {@code HashCode} instances into a {@code
347   * HashSet}) but is otherwise probably not what you want to use.
348   */
349  @Override
350  public final int hashCode() {
351    // If we have at least 4 bytes (32 bits), just take the first 4 bytes. Since this is
352    // already a (presumably) high-quality hash code, any four bytes of it will do.
353    if (bits() >= 32) {
354      return asInt();
355    }
356    // If we have less than 4 bytes, use them all.
357    byte[] bytes = asBytes();
358    int val = (bytes[0] & 0xFF);
359    for (int i = 1; i < bytes.length; i++) {
360      val |= ((bytes[i] & 0xFF) << (i * 8));
361    }
362    return val;
363  }
364
365  /**
366   * Returns a string containing each byte of {@link #asBytes}, in order, as a two-digit unsigned
367   * hexadecimal number in lower case.
368   *
369   * <p>Note that if the output is considered to be a single hexadecimal number, this hash code's
370   * bytes are the <i>big-endian</i> representation of that number. This may be surprising since
371   * everything else in the hashing API uniformly treats multibyte values as little-endian. But
372   * this format conveniently matches that of utilities such as the UNIX {@code md5sum} command.
373   *
374   * <p>To create a {@code HashCode} from its string representation, see {@link #fromString}.
375   */
376  @Override
377  public final String toString() {
378    byte[] bytes = asBytes();
379    StringBuilder sb = new StringBuilder(2 * bytes.length);
380    for (byte b : bytes) {
381      sb.append(hexDigits[(b >> 4) & 0xf]).append(hexDigits[b & 0xf]);
382    }
383    return sb.toString();
384  }
385
386  private static final char[] hexDigits = "0123456789abcdef".toCharArray();
387}