001/*
002 * Copyright (C) 2009 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package com.google.common.primitives;
018
019import static com.google.common.base.Preconditions.checkArgument;
020import static com.google.common.base.Preconditions.checkNotNull;
021
022import com.google.common.annotations.GwtCompatible;
023
024import java.util.Comparator;
025
026/**
027 * Static utility methods pertaining to {@code byte} primitives that
028 * interpret values as signed. The corresponding methods that treat the values
029 * as unsigned are found in {@link UnsignedBytes}, and the methods for which
030 * signedness is not an issue are in {@link Bytes}.
031 * 
032 * <p>See the Guava User Guide article on <a href=
033 * "http://code.google.com/p/guava-libraries/wiki/PrimitivesExplained">
034 * primitive utilities</a>.
035 *
036 * @author Kevin Bourrillion
037 * @since 1.0
038 */
039// TODO(kevinb): how to prevent warning on UnsignedBytes when building GWT
040// javadoc?
041@GwtCompatible
042public final class SignedBytes {
043  private SignedBytes() {}
044
045  /**
046   * The largest power of two that can be represented as a signed {@code byte}. 
047   *
048   * @since 10.0
049   */
050  public static final byte MAX_POWER_OF_TWO = 1 << 6;
051  
052  /**
053   * Returns the {@code byte} value that is equal to {@code value}, if possible.
054   *
055   * @param value any value in the range of the {@code byte} type
056   * @return the {@code byte} value that equals {@code value}
057   * @throws IllegalArgumentException if {@code value} is greater than {@link
058   *     Byte#MAX_VALUE} or less than {@link Byte#MIN_VALUE}
059   */
060  public static byte checkedCast(long value) {
061    byte result = (byte) value;
062    if (result != value) {
063      // don't use checkArgument here, to avoid boxing
064      throw new IllegalArgumentException("Out of range: " + value);
065    }
066    return result;
067  }
068
069  /**
070   * Returns the {@code byte} nearest in value to {@code value}.
071   *
072   * @param value any {@code long} value
073   * @return the same value cast to {@code byte} if it is in the range of the
074   *     {@code byte} type, {@link Byte#MAX_VALUE} if it is too large,
075   *     or {@link Byte#MIN_VALUE} if it is too small
076   */
077  public static byte saturatedCast(long value) {
078    if (value > Byte.MAX_VALUE) {
079      return Byte.MAX_VALUE;
080    }
081    if (value < Byte.MIN_VALUE) {
082      return Byte.MIN_VALUE;
083    }
084    return (byte) value;
085  }
086
087  /**
088   * Compares the two specified {@code byte} values. The sign of the value
089   * returned is the same as that of {@code ((Byte) a).compareTo(b)}.
090   *
091   * <p><b>Note:</b> this method behaves identically to the JDK 7 method {@link
092   * Byte#compare}.
093   *
094   * @param a the first {@code byte} to compare
095   * @param b the second {@code byte} to compare
096   * @return a negative value if {@code a} is less than {@code b}; a positive
097   *     value if {@code a} is greater than {@code b}; or zero if they are equal
098   */
099  // TODO(kevinb): if Ints.compare etc. are ever removed, *maybe* remove this
100  // one too, which would leave compare methods only on the Unsigned* classes.
101  public static int compare(byte a, byte b) {
102    return a - b; // safe due to restricted range
103  }
104
105  /**
106   * Returns the least value present in {@code array}.
107   *
108   * @param array a <i>nonempty</i> array of {@code byte} values
109   * @return the value present in {@code array} that is less than or equal to
110   *     every other value in the array
111   * @throws IllegalArgumentException if {@code array} is empty
112   */
113  public static byte min(byte... array) {
114    checkArgument(array.length > 0);
115    byte min = array[0];
116    for (int i = 1; i < array.length; i++) {
117      if (array[i] < min) {
118        min = array[i];
119      }
120    }
121    return min;
122  }
123
124  /**
125   * Returns the greatest value present in {@code array}.
126   *
127   * @param array a <i>nonempty</i> array of {@code byte} values
128   * @return the value present in {@code array} that is greater than or equal to
129   *     every other value in the array
130   * @throws IllegalArgumentException if {@code array} is empty
131   */
132  public static byte max(byte... array) {
133    checkArgument(array.length > 0);
134    byte max = array[0];
135    for (int i = 1; i < array.length; i++) {
136      if (array[i] > max) {
137        max = array[i];
138      }
139    }
140    return max;
141  }
142
143  /**
144   * Returns a string containing the supplied {@code byte} values separated
145   * by {@code separator}. For example, {@code join(":", 0x01, 0x02, -0x01)}
146   * returns the string {@code "1:2:-1"}.
147   *
148   * @param separator the text that should appear between consecutive values in
149   *     the resulting string (but not at the start or end)
150   * @param array an array of {@code byte} values, possibly empty
151   */
152  public static String join(String separator, byte... array) {
153    checkNotNull(separator);
154    if (array.length == 0) {
155      return "";
156    }
157
158    // For pre-sizing a builder, just get the right order of magnitude
159    StringBuilder builder = new StringBuilder(array.length * 5);
160    builder.append(array[0]);
161    for (int i = 1; i < array.length; i++) {
162      builder.append(separator).append(array[i]);
163    }
164    return builder.toString();
165  }
166
167  /**
168   * Returns a comparator that compares two {@code byte} arrays
169   * lexicographically. That is, it compares, using {@link
170   * #compare(byte, byte)}), the first pair of values that follow any common
171   * prefix, or when one array is a prefix of the other, treats the shorter
172   * array as the lesser. For example, {@code [] < [0x01] < [0x01, 0x80] <
173   * [0x01, 0x7F] < [0x02]}. Values are treated as signed.
174   *
175   * <p>The returned comparator is inconsistent with {@link
176   * Object#equals(Object)} (since arrays support only identity equality), but
177   * it is consistent with {@link java.util.Arrays#equals(byte[], byte[])}.
178   *
179   * @see <a href="http://en.wikipedia.org/wiki/Lexicographical_order">
180   *     Lexicographical order article at Wikipedia</a>
181   * @since 2.0
182   */
183  public static Comparator<byte[]> lexicographicalComparator() {
184    return LexicographicalComparator.INSTANCE;
185  }
186
187  private enum LexicographicalComparator implements Comparator<byte[]> {
188    INSTANCE;
189
190    @Override
191    public int compare(byte[] left, byte[] right) {
192      int minLength = Math.min(left.length, right.length);
193      for (int i = 0; i < minLength; i++) {
194        int result = SignedBytes.compare(left[i], right[i]);
195        if (result != 0) {
196          return result;
197        }
198      }
199      return left.length - right.length;
200    }
201  }
202}