1 /*
2 * Copyright (C) 2009 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
5 * in compliance with the License. You may obtain a copy of the License at
6 *
7 * http://www.apache.org/licenses/LICENSE-2.0
8 *
9 * Unless required by applicable law or agreed to in writing, software distributed under the License
10 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
11 * or implied. See the License for the specific language governing permissions and limitations under
12 * the License.
13 */
14
15 package com.google.common.primitives;
16
17 import static com.google.common.base.Preconditions.checkArgument;
18 import static com.google.common.base.Preconditions.checkNotNull;
19 import static com.google.common.base.Preconditions.checkPositionIndexes;
20 import static java.util.Objects.requireNonNull;
21
22 import com.google.common.annotations.Beta;
23 import com.google.common.annotations.GwtIncompatible;
24 import com.google.common.annotations.VisibleForTesting;
25 import com.google.errorprone.annotations.CanIgnoreReturnValue;
26 import java.nio.ByteOrder;
27 import java.util.Arrays;
28 import java.util.Comparator;
29 import sun.misc.Unsafe;
30
31 /**
32 * Static utility methods pertaining to {@code byte} primitives that interpret values as
33 * <i>unsigned</i> (that is, any negative value {@code b} is treated as the positive value {@code
34 * 256 + b}). The corresponding methods that treat the values as signed are found in {@link
35 * SignedBytes}, and the methods for which signedness is not an issue are in {@link Bytes}.
36 *
37 * <p>See the Guava User Guide article on <a
38 * href="https://github.com/google/guava/wiki/PrimitivesExplained">primitive utilities</a>.
39 *
40 * @author Kevin Bourrillion
41 * @author Martin Buchholz
42 * @author Hiroshi Yamauchi
43 * @author Louis Wasserman
44 * @since 1.0
45 */
46 @GwtIncompatible
47 @ElementTypesAreNonnullByDefault
48 public final class UnsignedBytes {
49 private UnsignedBytes() {}
50
51 /**
52 * The largest power of two that can be represented as an unsigned {@code byte}.
53 *
54 * @since 10.0
55 */
56 public static final byte MAX_POWER_OF_TWO = (byte) 0x80;
57
58 /**
59 * The largest value that fits into an unsigned byte.
60 *
61 * @since 13.0
62 */
63 public static final byte MAX_VALUE = (byte) 0xFF;
64
65 private static final int UNSIGNED_MASK = 0xFF;
66
67 /**
68 * Returns the value of the given byte as an integer, when treated as unsigned. That is, returns
69 * {@code value + 256} if {@code value} is negative; {@code value} itself otherwise.
70 *
71 * <p><b>Java 8 users:</b> use {@link Byte#toUnsignedInt(byte)} instead.
72 *
73 * @since 6.0
74 */
75 public static int toInt(byte value) {
76 return value & UNSIGNED_MASK;
77 }
78
79 /**
80 * Returns the {@code byte} value that, when treated as unsigned, is equal to {@code value}, if
81 * possible.
82 *
83 * @param value a value between 0 and 255 inclusive
84 * @return the {@code byte} value that, when treated as unsigned, equals {@code value}
85 * @throws IllegalArgumentException if {@code value} is negative or greater than 255
86 */
87 @CanIgnoreReturnValue
88 public static byte checkedCast(long value) {
89 checkArgument(value >> Byte.SIZE == 0, "out of range: %s", value);
90 return (byte) value;
91 }
92
93 /**
94 * Returns the {@code byte} value that, when treated as unsigned, is nearest in value to {@code
95 * value}.
96 *
97 * @param value any {@code long} value
98 * @return {@code (byte) 255} if {@code value >= 255}, {@code (byte) 0} if {@code value <= 0}, and
99 * {@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 }