giteadmin/script-astra
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity
4380f00a78
script-astra/Android/Sdk/sources/android-35/jdk/internal/util/ArraysSupport.java

813 lines
33 KiB
Java
Raw Normal View History

init
2025-01-20 15:15:20 +00:00
/*
* Copyright (c) 2015, 2023, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package jdk.internal.util;
import java.util.Arrays;
import java.util.Collection;
import jdk.internal.misc.Unsafe;
import jdk.internal.vm.annotation.IntrinsicCandidate;
/**
* Utility methods to work with arrays. This includes a set of methods
* to find a mismatch between two primitive arrays. Also included is
* a method to calculate the new length of an array to be reallocated.
*
* <p>Array equality and lexicographical comparison can be built on top of
* array mismatch functionality.
*
* <p>The mismatch method implementation, {@link #vectorizedMismatch}, leverages
* vector-based techniques to access and compare the contents of two arrays.
* The Java implementation uses {@code Unsafe.getLongUnaligned} to access the
* content of an array, thus access is supported on platforms that do not
* support unaligned access. For a byte[] array, 8 bytes (64 bits) can be
* accessed and compared as a unit rather than individually, which increases
* the performance when the method is compiled by the HotSpot VM. On supported
* platforms the mismatch implementation is intrinsified to leverage SIMD
* instructions. So for a byte[] array, 16 bytes (128 bits), 32 bytes
* (256 bits), and perhaps in the future even 64 bytes (512 bits), platform
* permitting, can be accessed and compared as a unit, which further increases
* the performance over the Java implementation.
*
* <p>None of the mismatch methods perform array bounds checks. It is the
* responsibility of the caller (direct or otherwise) to perform such checks
* before calling this method.
*/
public class ArraysSupport {
static final Unsafe U = Unsafe.getUnsafe();
// Android-changed: Android is little endian.
private static final boolean BIG_ENDIAN = false;
public static final int LOG2_ARRAY_BOOLEAN_INDEX_SCALE = exactLog2(Unsafe.ARRAY_BOOLEAN_INDEX_SCALE);
public static final int LOG2_ARRAY_BYTE_INDEX_SCALE = exactLog2(Unsafe.ARRAY_BYTE_INDEX_SCALE);
public static final int LOG2_ARRAY_CHAR_INDEX_SCALE = exactLog2(Unsafe.ARRAY_CHAR_INDEX_SCALE);
public static final int LOG2_ARRAY_SHORT_INDEX_SCALE = exactLog2(Unsafe.ARRAY_SHORT_INDEX_SCALE);
public static final int LOG2_ARRAY_INT_INDEX_SCALE = exactLog2(Unsafe.ARRAY_INT_INDEX_SCALE);
public static final int LOG2_ARRAY_LONG_INDEX_SCALE = exactLog2(Unsafe.ARRAY_LONG_INDEX_SCALE);
public static final int LOG2_ARRAY_FLOAT_INDEX_SCALE = exactLog2(Unsafe.ARRAY_FLOAT_INDEX_SCALE);
public static final int LOG2_ARRAY_DOUBLE_INDEX_SCALE = exactLog2(Unsafe.ARRAY_DOUBLE_INDEX_SCALE);
private static final int LOG2_BYTE_BIT_SIZE = exactLog2(Byte.SIZE);
private static int exactLog2(int scale) {
if ((scale & (scale - 1)) != 0)
throw new Error("data type scale not a power of two");
return Integer.numberOfTrailingZeros(scale);
}
private ArraysSupport() {}
/**
* Find the relative index of the first mismatching pair of elements in two
* primitive arrays of the same component type. Pairs of elements will be
* tested in order relative to given offsets into both arrays.
*
* <p>This method does not perform type checks or bounds checks. It is the
* responsibility of the caller to perform such checks before calling this
* method.
*
* <p>The given offsets, in bytes, need not be aligned according to the
* given log<sub>2</sub> size the array elements. More specifically, an
* offset modulus the size need not be zero.
*
* @param a the first array to be tested for mismatch, or {@code null} for
* direct memory access
* @param aOffset the relative offset, in bytes, from the base address of
* the first array to test from, otherwise if the first array is
* {@code null}, an absolute address pointing to the first element to test.
* @param b the second array to be tested for mismatch, or {@code null} for
* direct memory access
* @param bOffset the relative offset, in bytes, from the base address of
* the second array to test from, otherwise if the second array is
* {@code null}, an absolute address pointing to the first element to test.
* @param length the number of array elements to test
* @param log2ArrayIndexScale log<sub>2</sub> of the array index scale, that
* corresponds to the size, in bytes, of an array element.
* @return if a mismatch is found a relative index, between 0 (inclusive)
* and {@code length} (exclusive), of the first mismatching pair of elements
* in the two arrays. Otherwise, if a mismatch is not found the bitwise
* compliment of the number of remaining pairs of elements to be checked in
* the tail of the two arrays.
*/
@IntrinsicCandidate
public static int vectorizedMismatch(Object a, long aOffset,
Object b, long bOffset,
int length,
int log2ArrayIndexScale) {
// assert a.getClass().isArray();
// assert b.getClass().isArray();
// assert 0 <= length <= sizeOf(a)
// assert 0 <= length <= sizeOf(b)
// assert 0 <= log2ArrayIndexScale <= 3
int log2ValuesPerWidth = LOG2_ARRAY_LONG_INDEX_SCALE - log2ArrayIndexScale;
int wi = 0;
for (; wi < length >> log2ValuesPerWidth; wi++) {
long bi = ((long) wi) << LOG2_ARRAY_LONG_INDEX_SCALE;
long av = U.getLongUnaligned(a, aOffset + bi);
long bv = U.getLongUnaligned(b, bOffset + bi);
if (av != bv) {
long x = av ^ bv;
int o = BIG_ENDIAN
? Long.numberOfLeadingZeros(x) >> (LOG2_BYTE_BIT_SIZE + log2ArrayIndexScale)
: Long.numberOfTrailingZeros(x) >> (LOG2_BYTE_BIT_SIZE + log2ArrayIndexScale);
return (wi << log2ValuesPerWidth) + o;
}
}
// Calculate the tail of remaining elements to check
int tail = length - (wi << log2ValuesPerWidth);
if (log2ArrayIndexScale < LOG2_ARRAY_INT_INDEX_SCALE) {
int wordTail = 1 << (LOG2_ARRAY_INT_INDEX_SCALE - log2ArrayIndexScale);
// Handle 4 bytes or 2 chars in the tail using int width
if (tail >= wordTail) {
long bi = ((long) wi) << LOG2_ARRAY_LONG_INDEX_SCALE;
int av = U.getIntUnaligned(a, aOffset + bi);
int bv = U.getIntUnaligned(b, bOffset + bi);
if (av != bv) {
int x = av ^ bv;
int o = BIG_ENDIAN
? Integer.numberOfLeadingZeros(x) >> (LOG2_BYTE_BIT_SIZE + log2ArrayIndexScale)
: Integer.numberOfTrailingZeros(x) >> (LOG2_BYTE_BIT_SIZE + log2ArrayIndexScale);
return (wi << log2ValuesPerWidth) + o;
}
tail -= wordTail;
}
return ~tail;
}
else {
return ~tail;
}
}
// Possible values for the type operand of the NEWARRAY instruction.
// See https://docs.oracle.com/javase/specs/jvms/se9/html/jvms-6.html#jvms-6.5.newarray.
public static final int T_BOOLEAN = 4;
public static final int T_CHAR = 5;
public static final int T_FLOAT = 6;
public static final int T_DOUBLE = 7;
public static final int T_BYTE = 8;
public static final int T_SHORT = 9;
public static final int T_INT = 10;
public static final int T_LONG = 11;
/**
* Calculate the hash code for an array in a way that enables efficient
* vectorization.
*
* <p>This method does not perform type checks or bounds checks. It is the
* responsibility of the caller to perform such checks before calling this
* method.
*
* @param array for which to calculate hash code
* @param fromIndex start index, scaled to basicType
* @param length number of elements to include in the hash
* @param initialValue the initial value for the hash (typically constant 0 or 1)
* @param basicType type constant denoting how to interpret the array content.
* T_BOOLEAN is used to signify unsigned bytes, and T_CHAR might be used
* even if array is a byte[].
* @implNote currently basicType must be constant at the call site for this method
* to be intrinsified.
*
* @return the calculated hash value
*/
@IntrinsicCandidate
public static int vectorizedHashCode(Object array, int fromIndex, int length, int initialValue,
int basicType) {
return switch (basicType) {
case T_BOOLEAN -> signedHashCode(initialValue, (byte[]) array, fromIndex, length);
case T_CHAR -> array instanceof byte[]
? utf16hashCode(initialValue, (byte[]) array, fromIndex, length)
: hashCode(initialValue, (char[]) array, fromIndex, length);
case T_BYTE -> hashCode(initialValue, (byte[]) array, fromIndex, length);
case T_SHORT -> hashCode(initialValue, (short[]) array, fromIndex, length);
case T_INT -> hashCode(initialValue, (int[]) array, fromIndex, length);
default -> throw new IllegalArgumentException("unrecognized basic type: " + basicType);
};
}
private static int signedHashCode(int result, byte[] a, int fromIndex, int length) {
int end = fromIndex + length;
for (int i = fromIndex; i < end; i++) {
result = 31 * result + (a[i] & 0xff);
}
return result;
}
private static int hashCode(int result, byte[] a, int fromIndex, int length) {
int end = fromIndex + length;
for (int i = fromIndex; i < end; i++) {
result = 31 * result + a[i];
}
return result;
}
private static int hashCode(int result, char[] a, int fromIndex, int length) {
int end = fromIndex + length;
for (int i = fromIndex; i < end; i++) {
result = 31 * result + a[i];
}
return result;
}
private static int hashCode(int result, short[] a, int fromIndex, int length) {
int end = fromIndex + length;
for (int i = fromIndex; i < end; i++) {
result = 31 * result + a[i];
}
return result;
}
private static int hashCode(int result, int[] a, int fromIndex, int length) {
int end = fromIndex + length;
for (int i = fromIndex; i < end; i++) {
result = 31 * result + a[i];
}
return result;
}
// Android-removed: Make the StringUTF16 public on Android, and avoid JavaLangAccess.
// private static final JavaLangAccess JLA = SharedSecrets.getJavaLangAccess();
/*
* fromIndex and length must be scaled to char indexes.
*/
public static int utf16hashCode(int result, byte[] value, int fromIndex, int length) {
int end = fromIndex + length;
for (int i = fromIndex; i < end; i++) {
// Android-removed: Make the StringUTF16 public on Android, and avoid JavaLangAccess.
// result = 31 * result + JLA.getUTF16Char(value, i);
result = 31 * result + StringUTF16.getChar(value, i);
}
return result;
}
// Booleans
// Each boolean element takes up one byte
public static int mismatch(boolean[] a,
boolean[] b,
int length) {
int i = 0;
if (length > 7) {
if (a[0] != b[0])
return 0;
i = vectorizedMismatch(
a, Unsafe.ARRAY_BOOLEAN_BASE_OFFSET,
b, Unsafe.ARRAY_BOOLEAN_BASE_OFFSET,
length, LOG2_ARRAY_BOOLEAN_INDEX_SCALE);
if (i >= 0)
return i;
i = length - ~i;
}
for (; i < length; i++) {
if (a[i] != b[i])
return i;
}
return -1;
}
public static int mismatch(boolean[] a, int aFromIndex,
boolean[] b, int bFromIndex,
int length) {
int i = 0;
if (length > 7) {
if (a[aFromIndex] != b[bFromIndex])
return 0;
int aOffset = Unsafe.ARRAY_BOOLEAN_BASE_OFFSET + aFromIndex;
int bOffset = Unsafe.ARRAY_BOOLEAN_BASE_OFFSET + bFromIndex;
i = vectorizedMismatch(
a, aOffset,
b, bOffset,
length, LOG2_ARRAY_BOOLEAN_INDEX_SCALE);
if (i >= 0)
return i;
i = length - ~i;
}
for (; i < length; i++) {
if (a[aFromIndex + i] != b[bFromIndex + i])
return i;
}
return -1;
}
// Bytes
/**
* Find the index of a mismatch between two arrays.
*
* <p>This method does not perform bounds checks. It is the responsibility
* of the caller to perform such bounds checks before calling this method.
*
* @param a the first array to be tested for a mismatch
* @param b the second array to be tested for a mismatch
* @param length the number of bytes from each array to check
* @return the index of a mismatch between the two arrays, otherwise -1 if
* no mismatch. The index will be within the range of (inclusive) 0 to
* (exclusive) the smaller of the two array lengths.
*/
public static int mismatch(byte[] a,
byte[] b,
int length) {
// ISSUE: defer to index receiving methods if performance is good
// assert length <= a.length
// assert length <= b.length
int i = 0;
if (length > 7) {
if (a[0] != b[0])
return 0;
i = vectorizedMismatch(
a, Unsafe.ARRAY_BYTE_BASE_OFFSET,
b, Unsafe.ARRAY_BYTE_BASE_OFFSET,
length, LOG2_ARRAY_BYTE_INDEX_SCALE);
if (i >= 0)
return i;
// Align to tail
i = length - ~i;
// assert i >= 0 && i <= 7;
}
// Tail < 8 bytes
for (; i < length; i++) {
if (a[i] != b[i])
return i;
}
return -1;
}
/**
* Find the relative index of a mismatch between two arrays starting from
* given indexes.
*
* <p>This method does not perform bounds checks. It is the responsibility
* of the caller to perform such bounds checks before calling this method.
*
* @param a the first array to be tested for a mismatch
* @param aFromIndex the index of the first element (inclusive) in the first
* array to be compared
* @param b the second array to be tested for a mismatch
* @param bFromIndex the index of the first element (inclusive) in the
* second array to be compared
* @param length the number of bytes from each array to check
* @return the relative index of a mismatch between the two arrays,
* otherwise -1 if no mismatch. The index will be within the range of
* (inclusive) 0 to (exclusive) the smaller of the two array bounds.
*/
public static int mismatch(byte[] a, int aFromIndex,
byte[] b, int bFromIndex,
int length) {
// assert 0 <= aFromIndex < a.length
// assert 0 <= aFromIndex + length <= a.length
// assert 0 <= bFromIndex < b.length
// assert 0 <= bFromIndex + length <= b.length
// assert length >= 0
int i = 0;
if (length > 7) {
if (a[aFromIndex] != b[bFromIndex])
return 0;
int aOffset = Unsafe.ARRAY_BYTE_BASE_OFFSET + aFromIndex;
int bOffset = Unsafe.ARRAY_BYTE_BASE_OFFSET + bFromIndex;
i = vectorizedMismatch(
a, aOffset,
b, bOffset,
length, LOG2_ARRAY_BYTE_INDEX_SCALE);
if (i >= 0)
return i;
i = length - ~i;
}
for (; i < length; i++) {
if (a[aFromIndex + i] != b[bFromIndex + i])
return i;
}
return -1;
}
// Chars
public static int mismatch(char[] a,
char[] b,
int length) {
int i = 0;
if (length > 3) {
if (a[0] != b[0])
return 0;
i = vectorizedMismatch(
a, Unsafe.ARRAY_CHAR_BASE_OFFSET,
b, Unsafe.ARRAY_CHAR_BASE_OFFSET,
length, LOG2_ARRAY_CHAR_INDEX_SCALE);
if (i >= 0)
return i;
i = length - ~i;
}
for (; i < length; i++) {
if (a[i] != b[i])
return i;
}
return -1;
}
public static int mismatch(char[] a, int aFromIndex,
char[] b, int bFromIndex,
int length) {
int i = 0;
if (length > 3) {
if (a[aFromIndex] != b[bFromIndex])
return 0;
int aOffset = Unsafe.ARRAY_CHAR_BASE_OFFSET + (aFromIndex << LOG2_ARRAY_CHAR_INDEX_SCALE);
int bOffset = Unsafe.ARRAY_CHAR_BASE_OFFSET + (bFromIndex << LOG2_ARRAY_CHAR_INDEX_SCALE);
i = vectorizedMismatch(
a, aOffset,
b, bOffset,
length, LOG2_ARRAY_CHAR_INDEX_SCALE);
if (i >= 0)
return i;
i = length - ~i;
}
for (; i < length; i++) {
if (a[aFromIndex + i] != b[bFromIndex + i])
return i;
}
return -1;
}
// Shorts
public static int mismatch(short[] a,
short[] b,
int length) {
int i = 0;
if (length > 3) {
if (a[0] != b[0])
return 0;
i = vectorizedMismatch(
a, Unsafe.ARRAY_SHORT_BASE_OFFSET,
b, Unsafe.ARRAY_SHORT_BASE_OFFSET,
length, LOG2_ARRAY_SHORT_INDEX_SCALE);
if (i >= 0)
return i;
i = length - ~i;
}
for (; i < length; i++) {
if (a[i] != b[i])
return i;
}
return -1;
}
public static int mismatch(short[] a, int aFromIndex,
short[] b, int bFromIndex,
int length) {
int i = 0;
if (length > 3) {
if (a[aFromIndex] != b[bFromIndex])
return 0;
int aOffset = Unsafe.ARRAY_SHORT_BASE_OFFSET + (aFromIndex << LOG2_ARRAY_SHORT_INDEX_SCALE);
int bOffset = Unsafe.ARRAY_SHORT_BASE_OFFSET + (bFromIndex << LOG2_ARRAY_SHORT_INDEX_SCALE);
i = vectorizedMismatch(
a, aOffset,
b, bOffset,
length, LOG2_ARRAY_SHORT_INDEX_SCALE);
if (i >= 0)
return i;
i = length - ~i;
}
for (; i < length; i++) {
if (a[aFromIndex + i] != b[bFromIndex + i])
return i;
}
return -1;
}
// Ints
public static int mismatch(int[] a,
int[] b,
int length) {
int i = 0;
if (length > 1) {
if (a[0] != b[0])
return 0;
i = vectorizedMismatch(
a, Unsafe.ARRAY_INT_BASE_OFFSET,
b, Unsafe.ARRAY_INT_BASE_OFFSET,
length, LOG2_ARRAY_INT_INDEX_SCALE);
if (i >= 0)
return i;
i = length - ~i;
}
for (; i < length; i++) {
if (a[i] != b[i])
return i;
}
return -1;
}
public static int mismatch(int[] a, int aFromIndex,
int[] b, int bFromIndex,
int length) {
int i = 0;
if (length > 1) {
if (a[aFromIndex] != b[bFromIndex])
return 0;
int aOffset = Unsafe.ARRAY_INT_BASE_OFFSET + (aFromIndex << LOG2_ARRAY_INT_INDEX_SCALE);
int bOffset = Unsafe.ARRAY_INT_BASE_OFFSET + (bFromIndex << LOG2_ARRAY_INT_INDEX_SCALE);
i = vectorizedMismatch(
a, aOffset,
b, bOffset,
length, LOG2_ARRAY_INT_INDEX_SCALE);
if (i >= 0)
return i;
i = length - ~i;
}
for (; i < length; i++) {
if (a[aFromIndex + i] != b[bFromIndex + i])
return i;
}
return -1;
}
// Floats
public static int mismatch(float[] a,
float[] b,
int length) {
return mismatch(a, 0, b, 0, length);
}
public static int mismatch(float[] a, int aFromIndex,
float[] b, int bFromIndex,
int length) {
int i = 0;
if (length > 1) {
if (Float.floatToRawIntBits(a[aFromIndex]) == Float.floatToRawIntBits(b[bFromIndex])) {
int aOffset = Unsafe.ARRAY_FLOAT_BASE_OFFSET + (aFromIndex << LOG2_ARRAY_FLOAT_INDEX_SCALE);
int bOffset = Unsafe.ARRAY_FLOAT_BASE_OFFSET + (bFromIndex << LOG2_ARRAY_FLOAT_INDEX_SCALE);
i = vectorizedMismatch(
a, aOffset,
b, bOffset,
length, LOG2_ARRAY_FLOAT_INDEX_SCALE);
}
// Mismatched
if (i >= 0) {
// Check if mismatch is not associated with two NaN values
if (!Float.isNaN(a[aFromIndex + i]) || !Float.isNaN(b[bFromIndex + i]))
return i;
// Mismatch on two different NaN values that are normalized to match
// Fall back to slow mechanism
// ISSUE: Consider looping over vectorizedMismatch adjusting ranges
// However, requires that returned value be relative to input ranges
i++;
}
// Matched
else {
i = length - ~i;
}
}
for (; i < length; i++) {
if (Float.floatToIntBits(a[aFromIndex + i]) != Float.floatToIntBits(b[bFromIndex + i]))
return i;
}
return -1;
}
// 64 bit sizes
// Long
public static int mismatch(long[] a,
long[] b,
int length) {
if (length == 0) {
return -1;
}
if (a[0] != b[0])
return 0;
int i = vectorizedMismatch(
a, Unsafe.ARRAY_LONG_BASE_OFFSET,
b, Unsafe.ARRAY_LONG_BASE_OFFSET,
length, LOG2_ARRAY_LONG_INDEX_SCALE);
return i >= 0 ? i : -1;
}
public static int mismatch(long[] a, int aFromIndex,
long[] b, int bFromIndex,
int length) {
if (length == 0) {
return -1;
}
if (a[aFromIndex] != b[bFromIndex])
return 0;
int aOffset = Unsafe.ARRAY_LONG_BASE_OFFSET + (aFromIndex << LOG2_ARRAY_LONG_INDEX_SCALE);
int bOffset = Unsafe.ARRAY_LONG_BASE_OFFSET + (bFromIndex << LOG2_ARRAY_LONG_INDEX_SCALE);
int i = vectorizedMismatch(
a, aOffset,
b, bOffset,
length, LOG2_ARRAY_LONG_INDEX_SCALE);
return i >= 0 ? i : -1;
}
// Double
public static int mismatch(double[] a,
double[] b,
int length) {
return mismatch(a, 0, b, 0, length);
}
public static int mismatch(double[] a, int aFromIndex,
double[] b, int bFromIndex,
int length) {
if (length == 0) {
return -1;
}
int i = 0;
if (Double.doubleToRawLongBits(a[aFromIndex]) == Double.doubleToRawLongBits(b[bFromIndex])) {
int aOffset = Unsafe.ARRAY_DOUBLE_BASE_OFFSET + (aFromIndex << LOG2_ARRAY_DOUBLE_INDEX_SCALE);
int bOffset = Unsafe.ARRAY_DOUBLE_BASE_OFFSET + (bFromIndex << LOG2_ARRAY_DOUBLE_INDEX_SCALE);
i = vectorizedMismatch(
a, aOffset,
b, bOffset,
length, LOG2_ARRAY_DOUBLE_INDEX_SCALE);
}
if (i >= 0) {
// Check if mismatch is not associated with two NaN values
if (!Double.isNaN(a[aFromIndex + i]) || !Double.isNaN(b[bFromIndex + i]))
return i;
// Mismatch on two different NaN values that are normalized to match
// Fall back to slow mechanism
// ISSUE: Consider looping over vectorizedMismatch adjusting ranges
// However, requires that returned value be relative to input ranges
i++;
for (; i < length; i++) {
if (Double.doubleToLongBits(a[aFromIndex + i]) != Double.doubleToLongBits(b[bFromIndex + i]))
return i;
}
}
return -1;
}
/**
* A soft maximum array length imposed by array growth computations.
* Some JVMs (such as HotSpot) have an implementation limit that will cause
*
* OutOfMemoryError("Requested array size exceeds VM limit")
*
* to be thrown if a request is made to allocate an array of some length near
* Integer.MAX_VALUE, even if there is sufficient heap available. The actual
* limit might depend on some JVM implementation-specific characteristics such
* as the object header size. The soft maximum value is chosen conservatively so
* as to be smaller than any implementation limit that is likely to be encountered.
*/
public static final int SOFT_MAX_ARRAY_LENGTH = Integer.MAX_VALUE - 8;
/**
* Computes a new array length given an array's current length, a minimum growth
* amount, and a preferred growth amount. The computation is done in an overflow-safe
* fashion.
*
* This method is used by objects that contain an array that might need to be grown
* in order to fulfill some immediate need (the minimum growth amount) but would also
* like to request more space (the preferred growth amount) in order to accommodate
* potential future needs. The returned length is usually clamped at the soft maximum
* length in order to avoid hitting the JVM implementation limit. However, the soft
* maximum will be exceeded if the minimum growth amount requires it.
*
* If the preferred growth amount is less than the minimum growth amount, the
* minimum growth amount is used as the preferred growth amount.
*
* The preferred length is determined by adding the preferred growth amount to the
* current length. If the preferred length does not exceed the soft maximum length
* (SOFT_MAX_ARRAY_LENGTH) then the preferred length is returned.
*
* If the preferred length exceeds the soft maximum, we use the minimum growth
* amount. The minimum required length is determined by adding the minimum growth
* amount to the current length. If the minimum required length exceeds Integer.MAX_VALUE,
* then this method throws OutOfMemoryError. Otherwise, this method returns the greater of
* the soft maximum or the minimum required length.
*
* Note that this method does not do any array allocation itself; it only does array
* length growth computations. However, it will throw OutOfMemoryError as noted above.
*
* Note also that this method cannot detect the JVM's implementation limit, and it
* may compute and return a length value up to and including Integer.MAX_VALUE that
* might exceed the JVM's implementation limit. In that case, the caller will likely
* attempt an array allocation with that length and encounter an OutOfMemoryError.
* Of course, regardless of the length value returned from this method, the caller
* may encounter OutOfMemoryError if there is insufficient heap to fulfill the request.
*
* @param oldLength current length of the array (must be nonnegative)
* @param minGrowth minimum required growth amount (must be positive)
* @param prefGrowth preferred growth amount
* @return the new array length
* @throws OutOfMemoryError if the new length would exceed Integer.MAX_VALUE
*/
public static int newLength(int oldLength, int minGrowth, int prefGrowth) {
// preconditions not checked because of inlining
// assert oldLength >= 0
// assert minGrowth > 0
int prefLength = oldLength + Math.max(minGrowth, prefGrowth); // might overflow
if (0 < prefLength && prefLength <= SOFT_MAX_ARRAY_LENGTH) {
return prefLength;
} else {
// put code cold in a separate method
return hugeLength(oldLength, minGrowth);
}
}
private static int hugeLength(int oldLength, int minGrowth) {
int minLength = oldLength + minGrowth;
if (minLength < 0) { // overflow
throw new OutOfMemoryError(
"Required array length " + oldLength + " + " + minGrowth + " is too large");
} else if (minLength <= SOFT_MAX_ARRAY_LENGTH) {
return SOFT_MAX_ARRAY_LENGTH;
} else {
return minLength;
}
}
/**
* Reverses the elements of an array in-place.
*
* @param <T> the array component type
* @param a the array to be reversed
* @return the reversed array, always the same array as the argument
*/
public static <T> T[] reverse(T[] a) {
int limit = a.length / 2;
for (int i = 0, j = a.length - 1; i < limit; i++, j--) {
T t = a[i];
a[i] = a[j];
a[j] = t;
}
return a;
}
/**
* Dump the contents of the given collection into the given array, in reverse order.
* This mirrors the semantics of Collection.toArray(T[]) in regard to reusing the given
* array, appending null if necessary, or allocating a new array of the same component type.
* <p>
* A constraint is that this method should issue exactly one method call on the collection
* to obtain the elements and the size. Having a separate size() call or using an Iterator
* could result in errors if the collection changes size between calls. This implies that
* the elements need to be obtained via a single call to one of the toArray() methods.
* This further implies allocating memory proportional to the number of elements and
* making an extra copy, but this seems unavoidable.
* <p>
* An obvious approach would be simply to call coll.toArray(array) and then reverse the
* order of the elements. This doesn't work, because if given array is sufficiently long,
* we cannot tell how many elements were copied into it and thus there is no way to reverse
* the right set of elements while leaving the remaining array elements undisturbed.
*
* @throws ArrayStoreException if coll contains elements that can't be stored in the array
*/
public static <T> T[] toArrayReversed(Collection<?> coll, T[] array) {
T[] newArray = reverse(coll.toArray(Arrays.copyOfRange(array, 0, 0)));
if (newArray.length > array.length) {
return newArray;
} else {
System.arraycopy(newArray, 0, array, 0, newArray.length);
if (array.length > newArray.length) {
array[newArray.length] = null;
}
return array;
}
}
}
Reference in New Issue Copy Permalink