/*
* 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.VisibleForTesting;
// BEGIN android-changed
//import sun.misc.Unsafe;
// END android-changed
import java.lang.reflect.Field;
import java.nio.ByteOrder;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Comparator;
/**
* Static utility methods pertaining to {@code byte} primitives that interpret
* values as unsigned (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}.
*
* @author Kevin Bourrillion
* @author Martin Buchholz
* @author Hiroshi Yamauchi
* @since 1.0
*/
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) (1 << 7);
/**
* 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 & 0xFF;
}
/**
* 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
*/
public static byte checkedCast(long value) {
checkArgument(value >> 8 == 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 > 255) {
return (byte) 255; // -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 nonempty 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 nonempty 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 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 * 5);
builder.append(toInt(array[0]));
for (int i = 1; i < array.length; i++) {
builder.append(separator).append(toInt(array[i]));
}
return builder.toString();
}
/**
* Returns a comparator that compares two {@code byte} arrays
* lexicographically. 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.
*
*
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[])}.
*
* @see
* Lexicographical order article at Wikipedia
* @since 2.0
*/
public static Comparator lexicographicalComparator() {
return LexicographicalComparatorHolder.BEST_COMPARATOR;
}
@VisibleForTesting
static Comparator lexicographicalComparatorJavaImpl() {
return LexicographicalComparatorHolder.PureJavaComparator.INSTANCE;
}
/**
* Provides a lexicographical comparator implementation; either a Java
* implementation or a faster implementation based on {@link Unsafe}.
*
*
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";
// BEGIN android-changed
static final Comparator BEST_COMPARATOR = lexicographicalComparatorJavaImpl();
// @VisibleForTesting
// enum UnsafeComparator implements Comparator {
// INSTANCE;
// static final boolean littleEndian =
// ByteOrder.nativeOrder().equals(ByteOrder.LITTLE_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;
// /** The offset to the first element in a byte array. */
// static final int BYTE_ARRAY_BASE_OFFSET;
// static {
// theUnsafe = (Unsafe) AccessController.doPrivileged(
// new PrivilegedAction