/*
* Copyright (C) 2009 The Guava Authors
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
* in compliance with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software distributed under the License
* is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
* or implied. See the License for the specific language governing permissions and limitations under
* the License.
*/
package com.google.common.primitives;
import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.VisibleForTesting;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.nio.ByteOrder;
import java.util.Comparator;
import sun.misc.Unsafe;
/**
* Static utility methods pertaining to {@code byte} primitives that interpret values as
* <i>unsigned</i> (that is, any negative value {@code b} is treated as the positive value
* {@code 256 + b}). The corresponding methods that treat the values as signed are found in
* {@link SignedBytes}, and the methods for which signedness is not an issue are in {@link Bytes}.
*
* <p>See the Guava User Guide article on
* <a href="https://github.com/google/guava/wiki/PrimitivesExplained">primitive utilities</a>.
*
* @author Kevin Bourrillion
* @author Martin Buchholz
* @author Hiroshi Yamauchi
* @author Louis Wasserman
* @since 1.0
*/
@GwtIncompatible
public final class UnsignedBytes {
private UnsignedBytes() {}
/**
* The largest power of two that can be represented as an unsigned {@code
* byte}.
*
* @since 10.0
*/
public static final byte MAX_POWER_OF_TWO = (byte) 0x80;
/**
* The largest value that fits into an unsigned byte.
*
* @since 13.0
*/
public static final byte MAX_VALUE = (byte) 0xFF;
private static final int UNSIGNED_MASK = 0xFF;
/**
* Returns the value of the given byte as an integer, when treated as unsigned. That is, returns
* {@code value + 256} if {@code value} is negative; {@code value} itself otherwise.
*
* @since 6.0
*/
public static int toInt(byte value) {
return value & UNSIGNED_MASK;
}
/**
* Returns the {@code byte} value that, when treated as unsigned, is equal to {@code value}, if
* possible.
*
* @param value a value between 0 and 255 inclusive
* @return the {@code byte} value that, when treated as unsigned, equals {@code value}
* @throws IllegalArgumentException if {@code value} is negative or greater than 255
*/
@CanIgnoreReturnValue
public static byte checkedCast(long value) {
checkArgument(value >> Byte.SIZE == 0, "out of range: %s", value);
return (byte) value;
}
/**
* Returns the {@code byte} value that, when treated as unsigned, is nearest in value to
* {@code value}.
*
* @param value any {@code long} value
* @return {@code (byte) 255} if {@code value >= 255}, {@code (byte) 0} if {@code value <= 0}, and
* {@code value} cast to {@code byte} otherwise
*/
public static byte saturatedCast(long value) {
if (value > toInt(MAX_VALUE)) {
return MAX_VALUE; // -1
}
if (value < 0) {
return (byte) 0;
}
return (byte) value;
}
/**
* Compares the two specified {@code byte} values, treating them as unsigned values between 0 and
* 255 inclusive. For example, {@code (byte) -127} is considered greater than {@code (byte) 127}
* because it is seen as having the value of positive {@code 129}.
*
* @param a the first {@code byte} to compare
* @param b the second {@code byte} to compare
* @return a negative value if {@code a} is less than {@code b}; a positive value if {@code a} is
* greater than {@code b}; or zero if they are equal
*/
public static int compare(byte a, byte b) {
return toInt(a) - toInt(b);
}
/**
* Returns the least value present in {@code array}.
*
* @param array a <i>nonempty</i> array of {@code byte} values
* @return the value present in {@code array} that is less than or equal to every other value in
* the array
* @throws IllegalArgumentException if {@code array} is empty
*/
public static byte min(byte... array) {
checkArgument(array.length > 0);
int min = toInt(array[0]);
for (int i = 1; i < array.length; i++) {
int next = toInt(array[i]);
if (next < min) {
min = next;
}
}
return (byte) min;
}
/**
* Returns the greatest value present in {@code array}.
*
* @param array a <i>nonempty</i> array of {@code byte} values
* @return the value present in {@code array} that is greater than or equal to every other value
* in the array
* @throws IllegalArgumentException if {@code array} is empty
*/
public static byte max(byte... array) {
checkArgument(array.length > 0);
int max = toInt(array[0]);
for (int i = 1; i < array.length; i++) {
int next = toInt(array[i]);
if (next > max) {
max = next;
}
}
return (byte) max;
}
/**
* Returns a string representation of x, where x is treated as unsigned.
*
* @since 13.0
*/
@Beta
public static String toString(byte x) {
return toString(x, 10);
}
/**
* Returns a string representation of {@code x} for the given radix, where {@code x} is treated as
* unsigned.
*
* @param x the value to convert to a string.
* @param radix the radix to use while working with {@code x}
* @throws IllegalArgumentException if {@code radix} is not between {@link Character#MIN_RADIX}
* and {@link Character#MAX_RADIX}.
* @since 13.0
*/
@Beta
public static String toString(byte x, int radix) {
checkArgument(
radix >= Character.MIN_RADIX && radix <= Character.MAX_RADIX,
"radix (%s) must be between Character.MIN_RADIX and Character.MAX_RADIX",
radix);
// Benchmarks indicate this is probably not worth optimizing.
return Integer.toString(toInt(x), radix);
}
/**
* Returns the unsigned {@code byte} value represented by the given decimal string.
*
* @throws NumberFormatException if the string does not contain a valid unsigned {@code byte}
* value
* @throws NullPointerException if {@code string} is null (in contrast to
* {@link Byte#parseByte(String)})
* @since 13.0
*/
@Beta
@CanIgnoreReturnValue
public static byte parseUnsignedByte(String string) {
return parseUnsignedByte(string, 10);
}
/**
* Returns the unsigned {@code byte} value represented by a string with the given radix.
*
* @param string the string containing the unsigned {@code byte} representation to be parsed.
* @param radix the radix to use while parsing {@code string}
* @throws NumberFormatException if the string does not contain a valid unsigned {@code byte} with
* the given radix, or if {@code radix} is not between {@link Character#MIN_RADIX} and
* {@link Character#MAX_RADIX}.
* @throws NullPointerException if {@code string} is null (in contrast to
* {@link Byte#parseByte(String)})
* @since 13.0
*/
@Beta
@CanIgnoreReturnValue
public static byte parseUnsignedByte(String string, int radix) {
int parse = Integer.parseInt(checkNotNull(string), radix);
// We need to throw a NumberFormatException, so we have to duplicate checkedCast. =(
if (parse >> Byte.SIZE == 0) {
return (byte) parse;
} else {
throw new NumberFormatException("out of range: " + parse);
}
}
/**
* Returns a string containing the supplied {@code byte} values separated by {@code separator}.
* For example, {@code join(":", (byte) 1, (byte) 2,
* (byte) 255)} returns the string {@code "1:2:255"}.
*
* @param separator the text that should appear between consecutive values in the resulting string
* (but not at the start or end)
* @param array an array of {@code byte} values, possibly empty
*/
public static String join(String separator, byte... array) {
checkNotNull(separator);
if (array.length == 0) {
return "";
}
// For pre-sizing a builder, just get the right order of magnitude
StringBuilder builder = new StringBuilder(array.length * (3 + separator.length()));
builder.append(toInt(array[0]));
for (int i = 1; i < array.length; i++) {
builder.append(separator).append(toString(array[i]));
}
return builder.toString();
}
/**
* Returns a comparator that compares two {@code byte} arrays <a
* href="http://en.wikipedia.org/wiki/Lexicographical_order">lexicographically</a>. That is, it
* compares, using {@link #compare(byte, byte)}), the first pair of values that follow any common
* prefix, or when one array is a prefix of the other, treats the shorter array as the lesser. For
* example, {@code [] < [0x01] < [0x01, 0x7F] < [0x01, 0x80] < [0x02]}. Values are treated as
* unsigned.
*
* <p>The returned comparator is inconsistent with {@link Object#equals(Object)} (since arrays
* support only identity equality), but it is consistent with
* {@link java.util.Arrays#equals(byte[], byte[])}.
*
* @since 2.0
*/
public static Comparator<byte[]> lexicographicalComparator() {
return LexicographicalComparatorHolder.BEST_COMPARATOR;
}
@VisibleForTesting
static Comparator<byte[]> lexicographicalComparatorJavaImpl() {
return LexicographicalComparatorHolder.PureJavaComparator.INSTANCE;
}
/**
* Provides a lexicographical comparator implementation; either a Java implementation or a faster
* implementation based on {@link Unsafe}.
*
* <p>Uses reflection to gracefully fall back to the Java implementation if {@code Unsafe} isn't
* available.
*/
@VisibleForTesting
static class LexicographicalComparatorHolder {
static final String UNSAFE_COMPARATOR_NAME =
LexicographicalComparatorHolder.class.getName() + "$UnsafeComparator";
static final Comparator<byte[]> BEST_COMPARATOR = getBestComparator();
@VisibleForTesting
enum UnsafeComparator implements Comparator<byte[]> {
INSTANCE;
static final boolean BIG_ENDIAN = ByteOrder.nativeOrder().equals(ByteOrder.BIG_ENDIAN);
/*
* The following static final fields exist for performance reasons.
*
* In UnsignedBytesBenchmark, accessing the following objects via static final fields is the
* fastest (more than twice as fast as the Java implementation, vs ~1.5x with non-final static
* fields, on x86_32) under the Hotspot server compiler. The reason is obviously that the
* non-final fields need to be reloaded inside the loop.
*
* And, no, defining (final or not) local variables out of the loop still isn't as good
* because the null check on the theUnsafe object remains inside the loop and
* BYTE_ARRAY_BASE_OFFSET doesn't get constant-folded.
*
* The compiler can treat static final fields as compile-time constants and can constant-fold
* them while (final or not) local variables are run time values.
*/
static final Unsafe theUnsafe = getUnsafe();
/** The offset to the first element in a byte array. */
static final int BYTE_ARRAY_BASE_OFFSET = theUnsafe.arrayBaseOffset(byte[].class);
static {
// fall back to the safer pure java implementation unless we're in
// a 64-bit JVM with an 8-byte aligned field offset.
if (!("64".equals(System.getProperty("sun.arch.data.model"))
&& (BYTE_ARRAY_BASE_OFFSET % 8) == 0
// sanity check - this should never fail
&& theUnsafe.arrayIndexScale(byte[].class) == 1)) {
throw new Error(); // force fallback to PureJavaComparator
}
}
/**
* Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package. Replace with a simple
* call to Unsafe.getUnsafe when integrating into a jdk.
*
* @return a sun.misc.Unsafe
*/
private static sun.misc.Unsafe getUnsafe() {
try {
return sun.misc.Unsafe.getUnsafe();
} catch (SecurityException e) {
// that's okay; try reflection instead
}
try {
return java.security.AccessController.doPrivileged(
new java.security.PrivilegedExceptionAction<sun.misc.Unsafe>() {
@Override
public sun.misc.Unsafe run() throws Exception {
Class<sun.misc.Unsafe> k = sun.misc.Unsafe.class;
for (java.lang.reflect.Field f : k.getDeclaredFields()) {
f.setAccessible(true);
Object x = f.get(null);
if (k.isInstance(x)) {
return k.cast(x);
}
}
throw new NoSuchFieldError("the Unsafe");
}
});
} catch (java.security.PrivilegedActionException e) {
throw new RuntimeException("Could not initialize intrinsics", e.getCause());
}
}
@Override
public int compare(byte[] left, byte[] right) {
final int stride = 8;
int minLength = Math.min(left.length, right.length);
int strideLimit = minLength & ~(stride - 1);
int i;
/*
* Compare 8 bytes at a time. Benchmarking on x86 shows a stride of 8 bytes is no slower
* than 4 bytes even on 32-bit. On the other hand, it is substantially faster on 64-bit.
*/
for (i = 0; i < strideLimit; i += stride) {
long lw = theUnsafe.getLong(left, BYTE_ARRAY_BASE_OFFSET + (long) i);
long rw = theUnsafe.getLong(right, BYTE_ARRAY_BASE_OFFSET + (long) i);
if (lw != rw) {
if (BIG_ENDIAN) {
return UnsignedLongs.compare(lw, rw);
}
/*
* We want to compare only the first index where left[index] != right[index]. This
* corresponds to the least significant nonzero byte in lw ^ rw, since lw and rw are
* little-endian. Long.numberOfTrailingZeros(diff) tells us the least significant
* nonzero bit, and zeroing out the first three bits of L.nTZ gives us the shift to get
* that least significant nonzero byte.
*/
int n = Long.numberOfTrailingZeros(lw ^ rw) & ~0x7;
return ((int) ((lw >>> n) & UNSIGNED_MASK)) - ((int) ((rw >>> n) & UNSIGNED_MASK));
}
}
// The epilogue to cover the last (minLength % stride) elements.
for (; i < minLength; i++) {
int result = UnsignedBytes.compare(left[i], right[i]);
if (result != 0) {
return result;
}
}
return left.length - right.length;
}
@Override
public String toString() {
return "UnsignedBytes.lexicographicalComparator() (sun.misc.Unsafe version)";
}
}
enum PureJavaComparator implements Comparator<byte[]> {
INSTANCE;
@Override
public int compare(byte[] left, byte[] right) {
int minLength = Math.min(left.length, right.length);
for (int i = 0; i < minLength; i++) {
int result = UnsignedBytes.compare(left[i], right[i]);
if (result != 0) {
return result;
}
}
return left.length - right.length;
}
@Override
public String toString() {
return "UnsignedBytes.lexicographicalComparator() (pure Java version)";
}
}
/**
* Returns the Unsafe-using Comparator, or falls back to the pure-Java implementation if unable
* to do so.
*/
static Comparator<byte[]> getBestComparator() {
try {
Class<?> theClass = Class.forName(UNSAFE_COMPARATOR_NAME);
// yes, UnsafeComparator does implement Comparator<byte[]>
@SuppressWarnings("unchecked")
Comparator<byte[]> comparator = (Comparator<byte[]>) theClass.getEnumConstants()[0];
return comparator;
} catch (Throwable t) { // ensure we really catch *everything*
return lexicographicalComparatorJavaImpl();
}
}
}
}