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
017 package com.google.common.primitives;
018
019 import static com.google.common.base.Preconditions.checkArgument;
020 import static com.google.common.base.Preconditions.checkNotNull;
021
022 import com.google.common.annotations.Beta;
023 import com.google.common.annotations.VisibleForTesting;
024
025 import sun.misc.Unsafe;
026
027 import java.lang.reflect.Field;
028 import java.nio.ByteOrder;
029 import java.security.AccessController;
030 import java.security.PrivilegedAction;
031 import 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 */
050 public 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 }