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
010 * License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
011 * express or implied. See the License for the specific language governing permissions and
012 * limitations under the License.
013 */
014
015 package com.google.common.primitives;
016
017 import static com.google.common.base.Preconditions.checkArgument;
018 import static com.google.common.base.Preconditions.checkNotNull;
019
020 import com.google.common.annotations.Beta;
021 import com.google.common.annotations.GwtCompatible;
022
023 import java.util.Arrays;
024 import java.util.Comparator;
025
026 /**
027 * Static utility methods pertaining to {@code int} primitives that interpret values as
028 * <i>unsigned</i> (that is, any negative value {@code x} is treated as the positive value
029 * {@code 2^32 + x}). The methods for which signedness is not an issue are in {@link Ints}, as well
030 * as signed versions of methods for which signedness is an issue.
031 *
032 * <p>In addition, this class provides several static methods for converting an {@code int} to a
033 * {@code String} and a {@code String} to an {@code int} that treat the {@code int} as an unsigned
034 * number.
035 *
036 * <p>Users of these utilities must be <i>extremely careful</i> not to mix up signed and unsigned
037 * {@code int} values. When possible, it is recommended that the {@link UnsignedInteger} wrapper
038 * class be used, at a small efficiency penalty, to enforce the distinction in the type system.
039 *
040 * <p>See the Guava User Guide article on <a href=
041 * "http://code.google.com/p/guava-libraries/wiki/PrimitivesExplained#Unsigned_support">
042 * unsigned primitive utilities</a>.
043 *
044 * @author Louis Wasserman
045 * @since 11.0
046 */
047 @Beta
048 @GwtCompatible
049 public final class UnsignedInts {
050 static final long INT_MASK = 0xffffffffL;
051
052 private UnsignedInts() {}
053
054 static int flip(int value) {
055 return value ^ Integer.MIN_VALUE;
056 }
057
058 /**
059 * Compares the two specified {@code int} values, treating them as unsigned values between
060 * {@code 0} and {@code 2^32 - 1} inclusive.
061 *
062 * @param a the first unsigned {@code int} to compare
063 * @param b the second unsigned {@code int} to compare
064 * @return a negative value if {@code a} is less than {@code b}; a positive value if {@code a} is
065 * greater than {@code b}; or zero if they are equal
066 */
067 public static int compare(int a, int b) {
068 return Ints.compare(flip(a), flip(b));
069 }
070
071 /**
072 * Returns the value of the given {@code int} as a {@code long}, when treated as unsigned.
073 */
074 public static long toLong(int value) {
075 return value & INT_MASK;
076 }
077
078 /**
079 * Returns the least value present in {@code array}, treating values as unsigned.
080 *
081 * @param array a <i>nonempty</i> array of unsigned {@code int} values
082 * @return the value present in {@code array} that is less than or equal to every other value in
083 * the array according to {@link #compare}
084 * @throws IllegalArgumentException if {@code array} is empty
085 */
086 public static int min(int... array) {
087 checkArgument(array.length > 0);
088 int min = flip(array[0]);
089 for (int i = 1; i < array.length; i++) {
090 int next = flip(array[i]);
091 if (next < min) {
092 min = next;
093 }
094 }
095 return flip(min);
096 }
097
098 /**
099 * Returns the greatest value present in {@code array}, treating values as unsigned.
100 *
101 * @param array a <i>nonempty</i> array of unsigned {@code int} values
102 * @return the value present in {@code array} that is greater than or equal to every other value
103 * in the array according to {@link #compare}
104 * @throws IllegalArgumentException if {@code array} is empty
105 */
106 public static int max(int... array) {
107 checkArgument(array.length > 0);
108 int max = flip(array[0]);
109 for (int i = 1; i < array.length; i++) {
110 int next = flip(array[i]);
111 if (next > max) {
112 max = next;
113 }
114 }
115 return flip(max);
116 }
117
118 /**
119 * Returns a string containing the supplied unsigned {@code int} values separated by
120 * {@code separator}. For example, {@code join("-", 1, 2, 3)} returns the string {@code "1-2-3"}.
121 *
122 * @param separator the text that should appear between consecutive values in the resulting
123 * string (but not at the start or end)
124 * @param array an array of unsigned {@code int} values, possibly empty
125 */
126 public static String join(String separator, int... array) {
127 checkNotNull(separator);
128 if (array.length == 0) {
129 return "";
130 }
131
132 // For pre-sizing a builder, just get the right order of magnitude
133 StringBuilder builder = new StringBuilder(array.length * 5);
134 builder.append(toString(array[0]));
135 for (int i = 1; i < array.length; i++) {
136 builder.append(separator).append(toString(array[i]));
137 }
138 return builder.toString();
139 }
140
141 /**
142 * Returns a comparator that compares two arrays of unsigned {@code int} values lexicographically.
143 * That is, it compares, using {@link #compare(int, int)}), the first pair of values that follow
144 * any common prefix, or when one array is a prefix of the other, treats the shorter array as the
145 * lesser. For example, {@code [] < [1] < [1, 2] < [2] < [1 << 31]}.
146 *
147 * <p>The returned comparator is inconsistent with {@link Object#equals(Object)} (since arrays
148 * support only identity equality), but it is consistent with {@link Arrays#equals(int[], int[])}.
149 *
150 * @see <a href="http://en.wikipedia.org/wiki/Lexicographical_order"> Lexicographical order
151 * article at Wikipedia</a>
152 */
153 public static Comparator<int[]> lexicographicalComparator() {
154 return LexicographicalComparator.INSTANCE;
155 }
156
157 enum LexicographicalComparator implements Comparator<int[]> {
158 INSTANCE;
159
160 @Override
161 public int compare(int[] left, int[] right) {
162 int minLength = Math.min(left.length, right.length);
163 for (int i = 0; i < minLength; i++) {
164 if (left[i] != right[i]) {
165 return UnsignedInts.compare(left[i], right[i]);
166 }
167 }
168 return left.length - right.length;
169 }
170 }
171
172 /**
173 * Returns dividend / divisor, where the dividend and divisor are treated as unsigned 32-bit
174 * quantities.
175 *
176 * @param dividend the dividend (numerator)
177 * @param divisor the divisor (denominator)
178 * @throws ArithmeticException if divisor is 0
179 */
180 public static int divide(int dividend, int divisor) {
181 return (int) (toLong(dividend) / toLong(divisor));
182 }
183
184 /**
185 * Returns dividend % divisor, where the dividend and divisor are treated as unsigned 32-bit
186 * quantities.
187 *
188 * @param dividend the dividend (numerator)
189 * @param divisor the divisor (denominator)
190 * @throws ArithmeticException if divisor is 0
191 */
192 public static int remainder(int dividend, int divisor) {
193 return (int) (toLong(dividend) % toLong(divisor));
194 }
195
196 /**
197 * Returns the unsigned {@code int} value represented by the given decimal string.
198 *
199 * @throws NumberFormatException if the string does not contain a valid unsigned integer, or if
200 * the value represented is too large to fit in an unsigned {@code int}.
201 * @throws NullPointerException if {@code s} is null
202 */
203 public static int parseUnsignedInt(String s) {
204 return parseUnsignedInt(s, 10);
205 }
206
207 /**
208 * Returns the unsigned {@code int} value represented by a string with the given radix.
209 *
210 * @param string the string containing the unsigned integer representation to be parsed.
211 * @param radix the radix to use while parsing {@code s}; must be between
212 * {@link Character#MIN_RADIX} and {@link Character#MAX_RADIX}.
213 * @throws NumberFormatException if the string does not contain a valid unsigned {@code int}, or
214 * if supplied radix is invalid.
215 */
216 public static int parseUnsignedInt(String string, int radix) {
217 checkNotNull(string);
218 long result = Long.parseLong(string, radix);
219 if ((result & INT_MASK) != result) {
220 throw new NumberFormatException("Input " + string + " in base " + radix
221 + " is not in the range of an unsigned integer");
222 }
223 return (int) result;
224 }
225
226 /**
227 * Returns a string representation of x, where x is treated as unsigned.
228 */
229 public static String toString(int x) {
230 return toString(x, 10);
231 }
232
233 /**
234 * Returns a string representation of {@code x} for the given radix, where {@code x} is treated
235 * as unsigned.
236 *
237 * @param x the value to convert to a string.
238 * @param radix the radix to use while working with {@code x}
239 * @throws IllegalArgumentException if {@code radix} is not between {@link Character#MIN_RADIX}
240 * and {@link Character#MAX_RADIX}.
241 */
242 public static String toString(int x, int radix) {
243 long asLong = x & INT_MASK;
244 return Long.toString(asLong, radix);
245 }
246 }