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
015package com.google.common.primitives;
016
017import static com.google.common.base.Preconditions.checkArgument;
018import static com.google.common.base.Preconditions.checkNotNull;
019
020import com.google.common.annotations.Beta;
021import com.google.common.annotations.GwtCompatible;
022
023import java.util.Arrays;
024import 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
049public 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 string.
198   *
199   * Accepts a decimal, hexadecimal, or octal number given by specifying the following prefix:
200   *
201   * <ul>
202   * <li>{@code 0x}<i>HexDigits</i>
203   * <li>{@code 0X}<i>HexDigits</i>
204   * <li>{@code #}<i>HexDigits</i>
205   * <li>{@code 0}<i>OctalDigits</i>
206   * </ul>
207   *
208   * @throws NumberFormatException if the string does not contain a valid unsigned {@code int} value
209   * @since 13.0
210   */
211  public static int decode(String stringValue) {
212    ParseRequest request = ParseRequest.fromString(stringValue);
213
214    try {
215      return parseUnsignedInt(request.rawValue, request.radix);
216    } catch (NumberFormatException e) {
217      NumberFormatException decodeException =
218          new NumberFormatException("Error parsing value: " + stringValue);
219      decodeException.initCause(e);
220      throw decodeException;
221    }
222  }
223
224  /**
225   * Returns the unsigned {@code int} value represented by the given decimal string.
226   *
227   * @throws NumberFormatException if the string does not contain a valid unsigned {@code int} value
228   * @throws NullPointerException if {@code s} is null 
229   *         (in contrast to {@link Integer#parseInt(String)})
230   */
231  public static int parseUnsignedInt(String s) {
232    return parseUnsignedInt(s, 10);
233  }
234
235  /**
236   * Returns the unsigned {@code int} value represented by a string with the given radix.
237   *
238   * @param string the string containing the unsigned integer representation to be parsed.
239   * @param radix the radix to use while parsing {@code s}; must be between
240   *        {@link Character#MIN_RADIX} and {@link Character#MAX_RADIX}.
241   * @throws NumberFormatException if the string does not contain a valid unsigned {@code int}, or
242   *         if supplied radix is invalid.
243   * @throws NullPointerException if {@code s} is null 
244   *         (in contrast to {@link Integer#parseInt(String)})
245   */
246  public static int parseUnsignedInt(String string, int radix) {
247    checkNotNull(string);
248    long result = Long.parseLong(string, radix);
249    if ((result & INT_MASK) != result) {
250      throw new NumberFormatException("Input " + string + " in base " + radix
251          + " is not in the range of an unsigned integer");
252    }
253    return (int) result;
254  }
255
256  /**
257   * Returns a string representation of x, where x is treated as unsigned.
258   */
259  public static String toString(int x) {
260    return toString(x, 10);
261  }
262
263  /**
264   * Returns a string representation of {@code x} for the given radix, where {@code x} is treated
265   * as unsigned.
266   *
267   * @param x the value to convert to a string.
268   * @param radix the radix to use while working with {@code x}
269   * @throws IllegalArgumentException if {@code radix} is not between {@link Character#MIN_RADIX}
270   *         and {@link Character#MAX_RADIX}.
271   */
272  public static String toString(int x, int radix) {
273    long asLong = x & INT_MASK;
274    return Long.toString(asLong, radix);
275  }
276}