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    
017    package com.google.common.primitives;
018    
019    import static com.google.common.base.Preconditions.checkArgument;
020    import static com.google.common.base.Preconditions.checkNotNull;
021    
022    import com.google.common.annotations.GwtCompatible;
023    
024    import 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     * @author Kevin Bourrillion
033     * @since 1.0
034     */
035    // TODO(kevinb): how to prevent warning on UnsignedBytes when building GWT
036    // javadoc?
037    @GwtCompatible
038    public final class SignedBytes {
039      private SignedBytes() {}
040    
041      /**
042       * The largest power of two that can be represented as a signed {@code byte}. 
043       *
044       * @since 10.0
045       */
046      public static final byte MAX_POWER_OF_TWO = 1 << 6;
047      
048      /**
049       * Returns the {@code byte} value that is equal to {@code value}, if possible.
050       *
051       * @param value any value in the range of the {@code byte} type
052       * @return the {@code byte} value that equals {@code value}
053       * @throws IllegalArgumentException if {@code value} is greater than {@link
054       *     Byte#MAX_VALUE} or less than {@link Byte#MIN_VALUE}
055       */
056      public static byte checkedCast(long value) {
057        byte result = (byte) value;
058        checkArgument(result == value, "Out of range: %s", value);
059        return result;
060      }
061    
062      /**
063       * Returns the {@code byte} nearest in value to {@code value}.
064       *
065       * @param value any {@code long} value
066       * @return the same value cast to {@code byte} if it is in the range of the
067       *     {@code byte} type, {@link Byte#MAX_VALUE} if it is too large,
068       *     or {@link Byte#MIN_VALUE} if it is too small
069       */
070      public static byte saturatedCast(long value) {
071        if (value > Byte.MAX_VALUE) {
072          return Byte.MAX_VALUE;
073        }
074        if (value < Byte.MIN_VALUE) {
075          return Byte.MIN_VALUE;
076        }
077        return (byte) value;
078      }
079    
080      /**
081       * Compares the two specified {@code byte} values. The sign of the value
082       * returned is the same as that of {@code ((Byte) a).compareTo(b)}.
083       *
084       * @param a the first {@code byte} to compare
085       * @param b the second {@code byte} to compare
086       * @return a negative value if {@code a} is less than {@code b}; a positive
087       *     value if {@code a} is greater than {@code b}; or zero if they are equal
088       */
089      public static int compare(byte a, byte b) {
090        return a - b; // safe due to restricted range
091      }
092    
093      /**
094       * Returns the least value present in {@code array}.
095       *
096       * @param array a <i>nonempty</i> array of {@code byte} values
097       * @return the value present in {@code array} that is less than or equal to
098       *     every other value in the array
099       * @throws IllegalArgumentException if {@code array} is empty
100       */
101      public static byte min(byte... array) {
102        checkArgument(array.length > 0);
103        byte min = array[0];
104        for (int i = 1; i < array.length; i++) {
105          if (array[i] < min) {
106            min = array[i];
107          }
108        }
109        return min;
110      }
111    
112      /**
113       * Returns the greatest value present in {@code array}.
114       *
115       * @param array a <i>nonempty</i> array of {@code byte} values
116       * @return the value present in {@code array} that is greater than or equal to
117       *     every other value in the array
118       * @throws IllegalArgumentException if {@code array} is empty
119       */
120      public static byte max(byte... array) {
121        checkArgument(array.length > 0);
122        byte max = array[0];
123        for (int i = 1; i < array.length; i++) {
124          if (array[i] > max) {
125            max = array[i];
126          }
127        }
128        return max;
129      }
130    
131      /**
132       * Returns a string containing the supplied {@code byte} values separated
133       * by {@code separator}. For example, {@code join(":", 0x01, 0x02, -0x01)}
134       * returns the string {@code "1:2:-1"}.
135       *
136       * @param separator the text that should appear between consecutive values in
137       *     the resulting string (but not at the start or end)
138       * @param array an array of {@code byte} values, possibly empty
139       */
140      public static String join(String separator, byte... array) {
141        checkNotNull(separator);
142        if (array.length == 0) {
143          return "";
144        }
145    
146        // For pre-sizing a builder, just get the right order of magnitude
147        StringBuilder builder = new StringBuilder(array.length * 5);
148        builder.append(array[0]);
149        for (int i = 1; i < array.length; i++) {
150          builder.append(separator).append(array[i]);
151        }
152        return builder.toString();
153      }
154    
155      /**
156       * Returns a comparator that compares two {@code byte} arrays
157       * lexicographically. That is, it compares, using {@link
158       * #compare(byte, byte)}), the first pair of values that follow any common
159       * prefix, or when one array is a prefix of the other, treats the shorter
160       * array as the lesser. For example, {@code [] < [0x01] < [0x01, 0x80] <
161       * [0x01, 0x7F] < [0x02]}. Values are treated as signed.
162       *
163       * <p>The returned comparator is inconsistent with {@link
164       * Object#equals(Object)} (since arrays support only identity equality), but
165       * it is consistent with {@link java.util.Arrays#equals(byte[], byte[])}.
166       *
167       * @see <a href="http://en.wikipedia.org/wiki/Lexicographical_order">
168       *     Lexicographical order article at Wikipedia</a>
169       * @since 2.0
170       */
171      public static Comparator<byte[]> lexicographicalComparator() {
172        return LexicographicalComparator.INSTANCE;
173      }
174    
175      private enum LexicographicalComparator implements Comparator<byte[]> {
176        INSTANCE;
177    
178        @Override
179        public int compare(byte[] left, byte[] right) {
180          int minLength = Math.min(left.length, right.length);
181          for (int i = 0; i < minLength; i++) {
182            int result = SignedBytes.compare(left[i], right[i]);
183            if (result != 0) {
184              return result;
185            }
186          }
187          return left.length - right.length;
188        }
189      }
190    }