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     * <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
042    public 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        checkArgument(result == value, "Out of range: %s", value);
063        return result;
064      }
065    
066      /**
067       * Returns the {@code byte} nearest in value to {@code value}.
068       *
069       * @param value any {@code long} value
070       * @return the same value cast to {@code byte} if it is in the range of the
071       *     {@code byte} type, {@link Byte#MAX_VALUE} if it is too large,
072       *     or {@link Byte#MIN_VALUE} if it is too small
073       */
074      public static byte saturatedCast(long value) {
075        if (value > Byte.MAX_VALUE) {
076          return Byte.MAX_VALUE;
077        }
078        if (value < Byte.MIN_VALUE) {
079          return Byte.MIN_VALUE;
080        }
081        return (byte) value;
082      }
083    
084      /**
085       * Compares the two specified {@code byte} values. The sign of the value
086       * returned is the same as that of {@code ((Byte) a).compareTo(b)}.
087       *
088       * @param a the first {@code byte} to compare
089       * @param b the second {@code byte} to compare
090       * @return a negative value if {@code a} is less than {@code b}; a positive
091       *     value if {@code a} is greater than {@code b}; or zero if they are equal
092       */
093      public static int compare(byte a, byte b) {
094        return a - b; // safe due to restricted range
095      }
096    
097      /**
098       * Returns the least value present in {@code array}.
099       *
100       * @param array a <i>nonempty</i> array of {@code byte} values
101       * @return the value present in {@code array} that is less than or equal to
102       *     every other value in the array
103       * @throws IllegalArgumentException if {@code array} is empty
104       */
105      public static byte min(byte... array) {
106        checkArgument(array.length > 0);
107        byte min = array[0];
108        for (int i = 1; i < array.length; i++) {
109          if (array[i] < min) {
110            min = array[i];
111          }
112        }
113        return min;
114      }
115    
116      /**
117       * Returns the greatest value present in {@code array}.
118       *
119       * @param array a <i>nonempty</i> array of {@code byte} values
120       * @return the value present in {@code array} that is greater than or equal to
121       *     every other value in the array
122       * @throws IllegalArgumentException if {@code array} is empty
123       */
124      public static byte max(byte... array) {
125        checkArgument(array.length > 0);
126        byte max = array[0];
127        for (int i = 1; i < array.length; i++) {
128          if (array[i] > max) {
129            max = array[i];
130          }
131        }
132        return max;
133      }
134    
135      /**
136       * Returns a string containing the supplied {@code byte} values separated
137       * by {@code separator}. For example, {@code join(":", 0x01, 0x02, -0x01)}
138       * returns the string {@code "1:2:-1"}.
139       *
140       * @param separator the text that should appear between consecutive values in
141       *     the resulting string (but not at the start or end)
142       * @param array an array of {@code byte} values, possibly empty
143       */
144      public static String join(String separator, byte... array) {
145        checkNotNull(separator);
146        if (array.length == 0) {
147          return "";
148        }
149    
150        // For pre-sizing a builder, just get the right order of magnitude
151        StringBuilder builder = new StringBuilder(array.length * 5);
152        builder.append(array[0]);
153        for (int i = 1; i < array.length; i++) {
154          builder.append(separator).append(array[i]);
155        }
156        return builder.toString();
157      }
158    
159      /**
160       * Returns a comparator that compares two {@code byte} arrays
161       * lexicographically. That is, it compares, using {@link
162       * #compare(byte, byte)}), the first pair of values that follow any common
163       * prefix, or when one array is a prefix of the other, treats the shorter
164       * array as the lesser. For example, {@code [] < [0x01] < [0x01, 0x80] <
165       * [0x01, 0x7F] < [0x02]}. Values are treated as signed.
166       *
167       * <p>The returned comparator is inconsistent with {@link
168       * Object#equals(Object)} (since arrays support only identity equality), but
169       * it is consistent with {@link java.util.Arrays#equals(byte[], byte[])}.
170       *
171       * @see <a href="http://en.wikipedia.org/wiki/Lexicographical_order">
172       *     Lexicographical order article at Wikipedia</a>
173       * @since 2.0
174       */
175      public static Comparator<byte[]> lexicographicalComparator() {
176        return LexicographicalComparator.INSTANCE;
177      }
178    
179      private enum LexicographicalComparator implements Comparator<byte[]> {
180        INSTANCE;
181    
182        @Override
183        public int compare(byte[] left, byte[] right) {
184          int minLength = Math.min(left.length, right.length);
185          for (int i = 0; i < minLength; i++) {
186            int result = SignedBytes.compare(left[i], right[i]);
187            if (result != 0) {
188              return result;
189            }
190          }
191          return left.length - right.length;
192        }
193      }
194    }