001/*
002 * Copyright (C) 2009 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 License
010 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
011 * or implied. See the License for the specific language governing permissions and limitations under
012 * 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;
019import static com.google.common.base.Preconditions.checkPositionIndexes;
020import static java.util.Objects.requireNonNull;
021
022import com.google.common.annotations.Beta;
023import com.google.common.annotations.GwtIncompatible;
024import com.google.common.annotations.VisibleForTesting;
025import com.google.errorprone.annotations.CanIgnoreReturnValue;
026import java.nio.ByteOrder;
027import java.util.Arrays;
028import java.util.Comparator;
029import sun.misc.Unsafe;
030
031/**
032 * Static utility methods pertaining to {@code byte} primitives that interpret values as
033 * <i>unsigned</i> (that is, any negative value {@code b} is treated as the positive value {@code
034 * 256 + b}). The corresponding methods that treat the values as signed are found in {@link
035 * SignedBytes}, and the methods for which signedness is not an issue are in {@link Bytes}.
036 *
037 * <p>See the Guava User Guide article on <a
038 * href="https://github.com/google/guava/wiki/PrimitivesExplained">primitive utilities</a>.
039 *
040 * @author Kevin Bourrillion
041 * @author Martin Buchholz
042 * @author Hiroshi Yamauchi
043 * @author Louis Wasserman
044 * @since 1.0
045 */
046@GwtIncompatible
047@ElementTypesAreNonnullByDefault
048public final class UnsignedBytes {
049  private UnsignedBytes() {}
050
051  /**
052   * The largest power of two that can be represented as an unsigned {@code byte}.
053   *
054   * @since 10.0
055   */
056  public static final byte MAX_POWER_OF_TWO = (byte) 0x80;
057
058  /**
059   * The largest value that fits into an unsigned byte.
060   *
061   * @since 13.0
062   */
063  public static final byte MAX_VALUE = (byte) 0xFF;
064
065  private static final int UNSIGNED_MASK = 0xFF;
066
067  /**
068   * Returns the value of the given byte as an integer, when treated as unsigned. That is, returns
069   * {@code value + 256} if {@code value} is negative; {@code value} itself otherwise.
070   *
071   * <p><b>Java 8 users:</b> use {@link Byte#toUnsignedInt(byte)} instead.
072   *
073   * @since 6.0
074   */
075  public static int toInt(byte value) {
076    return value & UNSIGNED_MASK;
077  }
078
079  /**
080   * Returns the {@code byte} value that, when treated as unsigned, is equal to {@code value}, if
081   * possible.
082   *
083   * @param value a value between 0 and 255 inclusive
084   * @return the {@code byte} value that, when treated as unsigned, equals {@code value}
085   * @throws IllegalArgumentException if {@code value} is negative or greater than 255
086   */
087  @CanIgnoreReturnValue
088  public static byte checkedCast(long value) {
089    checkArgument(value >> Byte.SIZE == 0, "out of range: %s", value);
090    return (byte) value;
091  }
092
093  /**
094   * Returns the {@code byte} value that, when treated as unsigned, is nearest in value to {@code
095   * value}.
096   *
097   * @param value any {@code long} value
098   * @return {@code (byte) 255} if {@code value >= 255}, {@code (byte) 0} if {@code value <= 0}, and
099   *     {@code value} cast to {@code byte} otherwise
100   */
101  public static byte saturatedCast(long value) {
102    if (value > toInt(MAX_VALUE)) {
103      return MAX_VALUE; // -1
104    }
105    if (value < 0) {
106      return (byte) 0;
107    }
108    return (byte) value;
109  }
110
111  /**
112   * Compares the two specified {@code byte} values, treating them as unsigned values between 0 and
113   * 255 inclusive. For example, {@code (byte) -127} is considered greater than {@code (byte) 127}
114   * because it is seen as having the value of positive {@code 129}.
115   *
116   * @param a the first {@code byte} to compare
117   * @param b the second {@code byte} to compare
118   * @return a negative value if {@code a} is less than {@code b}; a positive value if {@code a} is
119   *     greater than {@code b}; or zero if they are equal
120   */
121  public static int compare(byte a, byte b) {
122    return toInt(a) - toInt(b);
123  }
124
125  /**
126   * Returns the least value present in {@code array}, treating values as unsigned.
127   *
128   * @param array a <i>nonempty</i> array of {@code byte} values
129   * @return the value present in {@code array} that is less than or equal to every other value in
130   *     the array according to {@link #compare}
131   * @throws IllegalArgumentException if {@code array} is empty
132   */
133  public static byte min(byte... array) {
134    checkArgument(array.length > 0);
135    int min = toInt(array[0]);
136    for (int i = 1; i < array.length; i++) {
137      int next = toInt(array[i]);
138      if (next < min) {
139        min = next;
140      }
141    }
142    return (byte) min;
143  }
144
145  /**
146   * Returns the greatest value present in {@code array}, treating values as unsigned.
147   *
148   * @param array a <i>nonempty</i> array of {@code byte} values
149   * @return the value present in {@code array} that is greater than or equal to every other value
150   *     in the array according to {@link #compare}
151   * @throws IllegalArgumentException if {@code array} is empty
152   */
153  public static byte max(byte... array) {
154    checkArgument(array.length > 0);
155    int max = toInt(array[0]);
156    for (int i = 1; i < array.length; i++) {
157      int next = toInt(array[i]);
158      if (next > max) {
159        max = next;
160      }
161    }
162    return (byte) max;
163  }
164
165  /**
166   * Returns a string representation of x, where x is treated as unsigned.
167   *
168   * @since 13.0
169   */
170  @Beta
171  public static String toString(byte x) {
172    return toString(x, 10);
173  }
174
175  /**
176   * Returns a string representation of {@code x} for the given radix, where {@code x} is treated as
177   * unsigned.
178   *
179   * @param x the value to convert to a string.
180   * @param radix the radix to use while working with {@code x}
181   * @throws IllegalArgumentException if {@code radix} is not between {@link Character#MIN_RADIX}
182   *     and {@link Character#MAX_RADIX}.
183   * @since 13.0
184   */
185  @Beta
186  public static String toString(byte x, int radix) {
187    checkArgument(
188        radix >= Character.MIN_RADIX && radix <= Character.MAX_RADIX,
189        "radix (%s) must be between Character.MIN_RADIX and Character.MAX_RADIX",
190        radix);
191    // Benchmarks indicate this is probably not worth optimizing.
192    return Integer.toString(toInt(x), radix);
193  }
194
195  /**
196   * Returns the unsigned {@code byte} value represented by the given decimal string.
197   *
198   * @throws NumberFormatException if the string does not contain a valid unsigned {@code byte}
199   *     value
200   * @throws NullPointerException if {@code string} is null (in contrast to {@link
201   *     Byte#parseByte(String)})
202   * @since 13.0
203   */
204  @Beta
205  @CanIgnoreReturnValue
206  public static byte parseUnsignedByte(String string) {
207    return parseUnsignedByte(string, 10);
208  }
209
210  /**
211   * Returns the unsigned {@code byte} value represented by a string with the given radix.
212   *
213   * @param string the string containing the unsigned {@code byte} representation to be parsed.
214   * @param radix the radix to use while parsing {@code string}
215   * @throws NumberFormatException if the string does not contain a valid unsigned {@code byte} with
216   *     the given radix, or if {@code radix} is not between {@link Character#MIN_RADIX} and {@link
217   *     Character#MAX_RADIX}.
218   * @throws NullPointerException if {@code string} is null (in contrast to {@link
219   *     Byte#parseByte(String)})
220   * @since 13.0
221   */
222  @Beta
223  @CanIgnoreReturnValue
224  public static byte parseUnsignedByte(String string, int radix) {
225    int parse = Integer.parseInt(checkNotNull(string), radix);
226    // We need to throw a NumberFormatException, so we have to duplicate checkedCast. =(
227    if (parse >> Byte.SIZE == 0) {
228      return (byte) parse;
229    } else {
230      throw new NumberFormatException("out of range: " + parse);
231    }
232  }
233
234  /**
235   * Returns a string containing the supplied {@code byte} values separated by {@code separator}.
236   * For example, {@code join(":", (byte) 1, (byte) 2, (byte) 255)} returns the string {@code
237   * "1:2:255"}.
238   *
239   * @param separator the text that should appear between consecutive values in the resulting string
240   *     (but not at the start or end)
241   * @param array an array of {@code byte} values, possibly empty
242   */
243  public static String join(String separator, byte... array) {
244    checkNotNull(separator);
245    if (array.length == 0) {
246      return "";
247    }
248
249    // For pre-sizing a builder, just get the right order of magnitude
250    StringBuilder builder = new StringBuilder(array.length * (3 + separator.length()));
251    builder.append(toInt(array[0]));
252    for (int i = 1; i < array.length; i++) {
253      builder.append(separator).append(toString(array[i]));
254    }
255    return builder.toString();
256  }
257
258  /**
259   * Returns a comparator that compares two {@code byte} arrays <a
260   * href="http://en.wikipedia.org/wiki/Lexicographical_order">lexicographically</a>. That is, it
261   * compares, using {@link #compare(byte, byte)}), the first pair of values that follow any common
262   * prefix, or when one array is a prefix of the other, treats the shorter array as the lesser. For
263   * example, {@code [] < [0x01] < [0x01, 0x7F] < [0x01, 0x80] < [0x02]}. Values are treated as
264   * unsigned.
265   *
266   * <p>The returned comparator is inconsistent with {@link Object#equals(Object)} (since arrays
267   * support only identity equality), but it is consistent with {@link
268   * java.util.Arrays#equals(byte[], byte[])}.
269   *
270   * @since 2.0
271   */
272  public static Comparator<byte[]> lexicographicalComparator() {
273    return LexicographicalComparatorHolder.BEST_COMPARATOR;
274  }
275
276  @VisibleForTesting
277  static Comparator<byte[]> lexicographicalComparatorJavaImpl() {
278    return LexicographicalComparatorHolder.PureJavaComparator.INSTANCE;
279  }
280
281  /**
282   * Provides a lexicographical comparator implementation; either a Java implementation or a faster
283   * implementation based on {@link Unsafe}.
284   *
285   * <p>Uses reflection to gracefully fall back to the Java implementation if {@code Unsafe} isn't
286   * available.
287   */
288  @VisibleForTesting
289  static class LexicographicalComparatorHolder {
290    static final String UNSAFE_COMPARATOR_NAME =
291        LexicographicalComparatorHolder.class.getName() + "$UnsafeComparator";
292
293    static final Comparator<byte[]> BEST_COMPARATOR = getBestComparator();
294
295    @VisibleForTesting
296    enum UnsafeComparator implements Comparator<byte[]> {
297      INSTANCE;
298
299      static final boolean BIG_ENDIAN = ByteOrder.nativeOrder().equals(ByteOrder.BIG_ENDIAN);
300
301      /*
302       * The following static final fields exist for performance reasons.
303       *
304       * In UnsignedBytesBenchmark, accessing the following objects via static final fields is the
305       * fastest (more than twice as fast as the Java implementation, vs ~1.5x with non-final static
306       * fields, on x86_32) 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 isn't as good
310       * because the null check on the theUnsafe object remains inside the loop and
311       * BYTE_ARRAY_BASE_OFFSET doesn't get constant-folded.
312       *
313       * The compiler can treat static final fields as compile-time constants and can constant-fold
314       * them while (final or not) local variables are run time values.
315       */
316
317      static final Unsafe theUnsafe = getUnsafe();
318
319      /** The offset to the first element in a byte array. */
320      static final int BYTE_ARRAY_BASE_OFFSET = theUnsafe.arrayBaseOffset(byte[].class);
321
322      static {
323        // fall back to the safer pure java implementation unless we're in
324        // a 64-bit JVM with an 8-byte aligned field offset.
325        if (!("64".equals(System.getProperty("sun.arch.data.model"))
326            && (BYTE_ARRAY_BASE_OFFSET % 8) == 0
327            // sanity check - this should never fail
328            && theUnsafe.arrayIndexScale(byte[].class) == 1)) {
329          throw new Error(); // force fallback to PureJavaComparator
330        }
331      }
332
333      /**
334       * Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package. Replace with a simple
335       * call to Unsafe.getUnsafe when integrating into a jdk.
336       *
337       * @return a sun.misc.Unsafe
338       */
339      private static sun.misc.Unsafe getUnsafe() {
340        try {
341          return sun.misc.Unsafe.getUnsafe();
342        } catch (SecurityException e) {
343          // that's okay; try reflection instead
344        }
345        try {
346          return java.security.AccessController.doPrivileged(
347              new java.security.PrivilegedExceptionAction<sun.misc.Unsafe>() {
348                @Override
349                public sun.misc.Unsafe run() throws Exception {
350                  Class<sun.misc.Unsafe> k = sun.misc.Unsafe.class;
351                  for (java.lang.reflect.Field f : k.getDeclaredFields()) {
352                    f.setAccessible(true);
353                    Object x = f.get(null);
354                    if (k.isInstance(x)) {
355                      return k.cast(x);
356                    }
357                  }
358                  throw new NoSuchFieldError("the Unsafe");
359                }
360              });
361        } catch (java.security.PrivilegedActionException e) {
362          throw new RuntimeException("Could not initialize intrinsics", e.getCause());
363        }
364      }
365
366      @Override
367      public int compare(byte[] left, byte[] right) {
368        final int stride = 8;
369        int minLength = Math.min(left.length, right.length);
370        int strideLimit = minLength & ~(stride - 1);
371        int i;
372
373        /*
374         * Compare 8 bytes at a time. Benchmarking on x86 shows a stride of 8 bytes is no slower
375         * than 4 bytes even on 32-bit. On the other hand, it is substantially faster on 64-bit.
376         */
377        for (i = 0; i < strideLimit; i += stride) {
378          long lw = theUnsafe.getLong(left, BYTE_ARRAY_BASE_OFFSET + (long) i);
379          long rw = theUnsafe.getLong(right, BYTE_ARRAY_BASE_OFFSET + (long) i);
380          if (lw != rw) {
381            if (BIG_ENDIAN) {
382              return UnsignedLongs.compare(lw, rw);
383            }
384
385            /*
386             * We want to compare only the first index where left[index] != right[index]. This
387             * corresponds to the least significant nonzero byte in lw ^ rw, since lw and rw are
388             * little-endian. Long.numberOfTrailingZeros(diff) tells us the least significant
389             * nonzero bit, and zeroing out the first three bits of L.nTZ gives us the shift to get
390             * that least significant nonzero byte.
391             */
392            int n = Long.numberOfTrailingZeros(lw ^ rw) & ~0x7;
393            return ((int) ((lw >>> n) & UNSIGNED_MASK)) - ((int) ((rw >>> n) & UNSIGNED_MASK));
394          }
395        }
396
397        // The epilogue to cover the last (minLength % stride) elements.
398        for (; i < minLength; i++) {
399          int result = UnsignedBytes.compare(left[i], right[i]);
400          if (result != 0) {
401            return result;
402          }
403        }
404        return left.length - right.length;
405      }
406
407      @Override
408      public String toString() {
409        return "UnsignedBytes.lexicographicalComparator() (sun.misc.Unsafe version)";
410      }
411    }
412
413    enum PureJavaComparator implements Comparator<byte[]> {
414      INSTANCE;
415
416      @Override
417      public int compare(byte[] left, byte[] right) {
418        int minLength = Math.min(left.length, right.length);
419        for (int i = 0; i < minLength; i++) {
420          int result = UnsignedBytes.compare(left[i], right[i]);
421          if (result != 0) {
422            return result;
423          }
424        }
425        return left.length - right.length;
426      }
427
428      @Override
429      public String toString() {
430        return "UnsignedBytes.lexicographicalComparator() (pure Java version)";
431      }
432    }
433
434    /**
435     * Returns the Unsafe-using Comparator, or falls back to the pure-Java implementation if unable
436     * to do so.
437     */
438    static Comparator<byte[]> getBestComparator() {
439      try {
440        Class<?> theClass = Class.forName(UNSAFE_COMPARATOR_NAME);
441
442        // requireNonNull is safe because the class is an enum.
443        Object[] constants = requireNonNull(theClass.getEnumConstants());
444
445        // yes, UnsafeComparator does implement Comparator<byte[]>
446        @SuppressWarnings("unchecked")
447        Comparator<byte[]> comparator = (Comparator<byte[]>) constants[0];
448        return comparator;
449      } catch (Throwable t) { // ensure we really catch *everything*
450        return lexicographicalComparatorJavaImpl();
451      }
452    }
453  }
454
455  private static byte flip(byte b) {
456    return (byte) (b ^ 0x80);
457  }
458
459  /**
460   * Sorts the array, treating its elements as unsigned bytes.
461   *
462   * @since 23.1
463   */
464  public static void sort(byte[] array) {
465    checkNotNull(array);
466    sort(array, 0, array.length);
467  }
468
469  /**
470   * Sorts the array between {@code fromIndex} inclusive and {@code toIndex} exclusive, treating its
471   * elements as unsigned bytes.
472   *
473   * @since 23.1
474   */
475  public static void sort(byte[] array, int fromIndex, int toIndex) {
476    checkNotNull(array);
477    checkPositionIndexes(fromIndex, toIndex, array.length);
478    for (int i = fromIndex; i < toIndex; i++) {
479      array[i] = flip(array[i]);
480    }
481    Arrays.sort(array, fromIndex, toIndex);
482    for (int i = fromIndex; i < toIndex; i++) {
483      array[i] = flip(array[i]);
484    }
485  }
486
487  /**
488   * Sorts the elements of {@code array} in descending order, interpreting them as unsigned 8-bit
489   * integers.
490   *
491   * @since 23.1
492   */
493  public static void sortDescending(byte[] array) {
494    checkNotNull(array);
495    sortDescending(array, 0, array.length);
496  }
497
498  /**
499   * Sorts the elements of {@code array} between {@code fromIndex} inclusive and {@code toIndex}
500   * exclusive in descending order, interpreting them as unsigned 8-bit integers.
501   *
502   * @since 23.1
503   */
504  public static void sortDescending(byte[] array, int fromIndex, int toIndex) {
505    checkNotNull(array);
506    checkPositionIndexes(fromIndex, toIndex, array.length);
507    for (int i = fromIndex; i < toIndex; i++) {
508      array[i] ^= Byte.MAX_VALUE;
509    }
510    Arrays.sort(array, fromIndex, toIndex);
511    for (int i = fromIndex; i < toIndex; i++) {
512      array[i] ^= Byte.MAX_VALUE;
513    }
514  }
515}