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.Beta;
023import com.google.common.annotations.VisibleForTesting;
024
025import sun.misc.Unsafe;
026
027import java.lang.reflect.Field;
028import java.nio.ByteOrder;
029import java.security.AccessController;
030import java.security.PrivilegedAction;
031import java.util.Comparator;
032
033/**
034 * Static utility methods pertaining to {@code byte} primitives that interpret
035 * values as <i>unsigned</i> (that is, any negative value {@code b} is treated
036 * as the positive value {@code 256 + b}). The corresponding methods that treat
037 * the values as signed are found in {@link SignedBytes}, and the methods for
038 * which signedness is not an issue are in {@link Bytes}.
039 *
040 * <p>See the Guava User Guide article on <a href=
041 * "http://code.google.com/p/guava-libraries/wiki/PrimitivesExplained">
042 * primitive utilities</a>.
043 *
044 * @author Kevin Bourrillion
045 * @author Martin Buchholz
046 * @author Hiroshi Yamauchi
047 * @author Louis Wasserman
048 * @since 1.0
049 */
050public final class UnsignedBytes {
051  private UnsignedBytes() {}
052
053  /**
054   * The largest power of two that can be represented as an unsigned {@code
055   * byte}.
056   *
057   * @since 10.0
058   */
059  public static final byte MAX_POWER_OF_TWO = (byte) 0x80;
060
061  /**
062   * The largest value that fits into an unsigned byte.
063   *
064   * @since 13.0
065   */
066  public static final byte MAX_VALUE = (byte) 0xFF;
067
068  private static final int UNSIGNED_MASK = 0xFF;
069
070  /**
071   * Returns the value of the given byte as an integer, when treated as
072   * unsigned. That is, returns {@code value + 256} if {@code value} is
073   * negative; {@code value} itself otherwise.
074   *
075   * @since 6.0
076   */
077  public static int toInt(byte value) {
078    return value & UNSIGNED_MASK;
079  }
080
081  /**
082   * Returns the {@code byte} value that, when treated as unsigned, is equal to
083   * {@code value}, if possible.
084   *
085   * @param value a value between 0 and 255 inclusive
086   * @return the {@code byte} value that, when treated as unsigned, equals
087   *     {@code value}
088   * @throws IllegalArgumentException if {@code value} is negative or greater
089   *     than 255
090   */
091  public static byte checkedCast(long value) {
092    checkArgument(value >> Byte.SIZE == 0, "out of range: %s", value);
093    return (byte) value;
094  }
095
096  /**
097   * Returns the {@code byte} value that, when treated as unsigned, is nearest
098   * in value to {@code value}.
099   *
100   * @param value any {@code long} value
101   * @return {@code (byte) 255} if {@code value >= 255}, {@code (byte) 0} if
102   *     {@code value <= 0}, and {@code value} cast to {@code byte} otherwise
103   */
104  public static byte saturatedCast(long value) {
105    if (value > toInt(MAX_VALUE)) {
106      return MAX_VALUE; // -1
107    }
108    if (value < 0) {
109      return (byte) 0;
110    }
111    return (byte) value;
112  }
113
114  /**
115   * Compares the two specified {@code byte} values, treating them as unsigned
116   * values between 0 and 255 inclusive. For example, {@code (byte) -127} is
117   * considered greater than {@code (byte) 127} because it is seen as having
118   * the value of positive {@code 129}.
119   *
120   * @param a the first {@code byte} to compare
121   * @param b the second {@code byte} to compare
122   * @return a negative value if {@code a} is less than {@code b}; a positive
123   *     value if {@code a} is greater than {@code b}; or zero if they are equal
124   */
125  public static int compare(byte a, byte b) {
126    return toInt(a) - toInt(b);
127  }
128
129  /**
130   * Returns the least value present in {@code array}.
131   *
132   * @param array a <i>nonempty</i> array of {@code byte} values
133   * @return the value present in {@code array} that is less than or equal to
134   *     every other value in the array
135   * @throws IllegalArgumentException if {@code array} is empty
136   */
137  public static byte min(byte... array) {
138    checkArgument(array.length > 0);
139    int min = toInt(array[0]);
140    for (int i = 1; i < array.length; i++) {
141      int next = toInt(array[i]);
142      if (next < min) {
143        min = next;
144      }
145    }
146    return (byte) min;
147  }
148
149  /**
150   * Returns the greatest value present in {@code array}.
151   *
152   * @param array a <i>nonempty</i> array of {@code byte} values
153   * @return the value present in {@code array} that is greater than or equal
154   *     to every other value in the array
155   * @throws IllegalArgumentException if {@code array} is empty
156   */
157  public static byte max(byte... array) {
158    checkArgument(array.length > 0);
159    int max = toInt(array[0]);
160    for (int i = 1; i < array.length; i++) {
161      int next = toInt(array[i]);
162      if (next > max) {
163        max = next;
164      }
165    }
166    return (byte) max;
167  }
168
169  /**
170   * Returns a string representation of x, where x is treated as unsigned.
171   *
172   * @since 13.0
173   */
174  @Beta
175  public static String toString(byte x) {
176    return toString(x, 10);
177  }
178
179  /**
180   * Returns a string representation of {@code x} for the given radix, where {@code x} is treated
181   * as unsigned.
182   *
183   * @param x the value to convert to a string.
184   * @param radix the radix to use while working with {@code x}
185   * @throws IllegalArgumentException if {@code radix} is not between {@link Character#MIN_RADIX}
186   *         and {@link Character#MAX_RADIX}.
187   * @since 13.0
188   */
189  @Beta
190  public static String toString(byte x, int radix) {
191    checkArgument(radix >= Character.MIN_RADIX && radix <= Character.MAX_RADIX,
192        "radix (%s) must be between Character.MIN_RADIX and Character.MAX_RADIX", radix);
193    // Benchmarks indicate this is probably not worth optimizing.
194    return Integer.toString(toInt(x), radix);
195  }
196
197  /**
198   * Returns the unsigned {@code byte} value represented by the given decimal string.
199   *
200   * @throws NumberFormatException if the string does not contain a valid unsigned {@code long}
201   *         value
202   * @since 13.0
203   */
204  @Beta
205  public static byte parseUnsignedByte(String string) {
206    return parseUnsignedByte(string, 10);
207  }
208
209  /**
210   * Returns the unsigned {@code byte} value represented by a string with the given radix.
211   *
212   * @param string the string containing the unsigned {@code byte} representation to be parsed.
213   * @param radix the radix to use while parsing {@code string}
214   * @throws NumberFormatException if the string does not contain a valid unsigned {@code byte}
215   *         with the given radix, or if {@code radix} is not between {@link Character#MIN_RADIX}
216   *         and {@link Character#MAX_RADIX}.
217   * @since 13.0
218   */
219  @Beta
220  public static byte parseUnsignedByte(String string, int radix) {
221    int parse = Integer.parseInt(checkNotNull(string), radix);
222    // We need to throw a NumberFormatException, so we have to duplicate checkedCast. =(
223    if (parse >> Byte.SIZE == 0) {
224      return (byte) parse;
225    } else {
226      throw new NumberFormatException("out of range: " + parse);
227    }
228  }
229
230  /**
231   * Returns a string containing the supplied {@code byte} values separated by
232   * {@code separator}. For example, {@code join(":", (byte) 1, (byte) 2,
233   * (byte) 255)} returns the string {@code "1:2:255"}.
234   *
235   * @param separator the text that should appear between consecutive values in
236   *     the resulting string (but not at the start or end)
237   * @param array an array of {@code byte} values, possibly empty
238   */
239  public static String join(String separator, byte... array) {
240    checkNotNull(separator);
241    if (array.length == 0) {
242      return "";
243    }
244
245    // For pre-sizing a builder, just get the right order of magnitude
246    StringBuilder builder = new StringBuilder(array.length * (3 + separator.length()));
247    builder.append(toInt(array[0]));
248    for (int i = 1; i < array.length; i++) {
249      builder.append(separator).append(toString(array[i]));
250    }
251    return builder.toString();
252  }
253
254  /**
255   * Returns a comparator that compares two {@code byte} arrays
256   * lexicographically. That is, it compares, using {@link
257   * #compare(byte, byte)}), the first pair of values that follow any common
258   * prefix, or when one array is a prefix of the other, treats the shorter
259   * array as the lesser. For example, {@code [] < [0x01] < [0x01, 0x7F] <
260   * [0x01, 0x80] < [0x02]}. Values are treated as unsigned.
261   *
262   * <p>The returned comparator is inconsistent with {@link
263   * Object#equals(Object)} (since arrays support only identity equality), but
264   * it is consistent with {@link java.util.Arrays#equals(byte[], byte[])}.
265   *
266   * @see <a href="http://en.wikipedia.org/wiki/Lexicographical_order">
267   *     Lexicographical order article at Wikipedia</a>
268   * @since 2.0
269   */
270  public static Comparator<byte[]> lexicographicalComparator() {
271    return LexicographicalComparatorHolder.BEST_COMPARATOR;
272  }
273
274  @VisibleForTesting
275  static Comparator<byte[]> lexicographicalComparatorJavaImpl() {
276    return LexicographicalComparatorHolder.PureJavaComparator.INSTANCE;
277  }
278
279  /**
280   * Provides a lexicographical comparator implementation; either a Java
281   * implementation or a faster implementation based on {@link Unsafe}.
282   *
283   * <p>Uses reflection to gracefully fall back to the Java implementation if
284   * {@code Unsafe} isn't available.
285   */
286  @VisibleForTesting
287  static class LexicographicalComparatorHolder {
288    static final String UNSAFE_COMPARATOR_NAME =
289        LexicographicalComparatorHolder.class.getName() + "$UnsafeComparator";
290
291    static final Comparator<byte[]> BEST_COMPARATOR = getBestComparator();
292
293    @VisibleForTesting
294    enum UnsafeComparator implements Comparator<byte[]> {
295      INSTANCE;
296
297      static final boolean littleEndian =
298          ByteOrder.nativeOrder().equals(ByteOrder.LITTLE_ENDIAN);
299
300      /*
301       * The following static final fields exist for performance reasons.
302       *
303       * In UnsignedBytesBenchmark, accessing the following objects via static
304       * final fields is the fastest (more than twice as fast as the Java
305       * implementation, vs ~1.5x with non-final static fields, on x86_32)
306       * under the Hotspot server compiler. The reason is obviously that the
307       * non-final fields need to be reloaded inside the loop.
308       *
309       * And, no, defining (final or not) local variables out of the loop still
310       * isn't as good because the null check on the theUnsafe object remains
311       * inside the loop and BYTE_ARRAY_BASE_OFFSET doesn't get
312       * constant-folded.
313       *
314       * The compiler can treat static final fields as compile-time constants
315       * and can constant-fold them while (final or not) local variables are
316       * run time values.
317       */
318
319      static final Unsafe theUnsafe;
320
321      /** The offset to the first element in a byte array. */
322      static final int BYTE_ARRAY_BASE_OFFSET;
323
324      static {
325        theUnsafe = (Unsafe) AccessController.doPrivileged(
326            new PrivilegedAction<Object>() {
327              @Override
328              public Object run() {
329                try {
330                  Field f = Unsafe.class.getDeclaredField("theUnsafe");
331                  f.setAccessible(true);
332                  return f.get(null);
333                } catch (NoSuchFieldException e) {
334                  // It doesn't matter what we throw;
335                  // it's swallowed in getBestComparator().
336                  throw new Error();
337                } catch (IllegalAccessException e) {
338                  throw new Error();
339                }
340              }
341            });
342
343        BYTE_ARRAY_BASE_OFFSET = theUnsafe.arrayBaseOffset(byte[].class);
344
345        // sanity check - this should never fail
346        if (theUnsafe.arrayIndexScale(byte[].class) != 1) {
347          throw new AssertionError();
348        }
349      }
350
351      @Override public int compare(byte[] left, byte[] right) {
352        int minLength = Math.min(left.length, right.length);
353        int minWords = minLength / Longs.BYTES;
354
355        /*
356         * Compare 8 bytes at a time. Benchmarking shows comparing 8 bytes at a
357         * time is no slower than comparing 4 bytes at a time even on 32-bit.
358         * On the other hand, it is substantially faster on 64-bit.
359         */
360        for (int i = 0; i < minWords * Longs.BYTES; i += Longs.BYTES) {
361          long lw = theUnsafe.getLong(left, BYTE_ARRAY_BASE_OFFSET + (long) i);
362          long rw = theUnsafe.getLong(right, BYTE_ARRAY_BASE_OFFSET + (long) i);
363          long diff = lw ^ rw;
364
365          if (diff != 0) {
366            if (!littleEndian) {
367              return UnsignedLongs.compare(lw, rw);
368            }
369
370            // Use binary search
371            int n = 0;
372            int y;
373            int x = (int) diff;
374            if (x == 0) {
375              x = (int) (diff >>> 32);
376              n = 32;
377            }
378
379            y = x << 16;
380            if (y == 0) {
381              n += 16;
382            } else {
383              x = y;
384            }
385
386            y = x << 8;
387            if (y == 0) {
388              n += 8;
389            }
390            return (int) (((lw >>> n) & UNSIGNED_MASK) - ((rw >>> n) & UNSIGNED_MASK));
391          }
392        }
393
394        // The epilogue to cover the last (minLength % 8) elements.
395        for (int i = minWords * Longs.BYTES; i < minLength; i++) {
396          int result = UnsignedBytes.compare(left[i], right[i]);
397          if (result != 0) {
398            return result;
399          }
400        }
401        return left.length - right.length;
402      }
403    }
404
405    enum PureJavaComparator implements Comparator<byte[]> {
406      INSTANCE;
407
408      @Override public int compare(byte[] left, byte[] right) {
409        int minLength = Math.min(left.length, right.length);
410        for (int i = 0; i < minLength; i++) {
411          int result = UnsignedBytes.compare(left[i], right[i]);
412          if (result != 0) {
413            return result;
414          }
415        }
416        return left.length - right.length;
417      }
418    }
419
420    /**
421     * Returns the Unsafe-using Comparator, or falls back to the pure-Java
422     * implementation if unable to do so.
423     */
424    static Comparator<byte[]> getBestComparator() {
425      try {
426        Class<?> theClass = Class.forName(UNSAFE_COMPARATOR_NAME);
427
428        // yes, UnsafeComparator does implement Comparator<byte[]>
429        @SuppressWarnings("unchecked")
430        Comparator<byte[]> comparator =
431            (Comparator<byte[]>) theClass.getEnumConstants()[0];
432        return comparator;
433      } catch (Throwable t) { // ensure we really catch *everything*
434        return lexicographicalComparatorJavaImpl();
435      }
436    }
437  }
438}