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/*
* Copyright 2013 Google Inc.
*
* 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.jimfs;
import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import com.google.common.collect.ImmutableCollection;
/**
* Miscellaneous static utility methods.
*
* @author Colin Decker
* @author Austin Appleby
*/
final class Util {
private Util() {}
/** Returns the next power of 2 >= n. */
public static int nextPowerOf2(int n) {
if (n == 0) {
return 1;
}
int b = Integer.highestOneBit(n);
return b == n ? n : b << 1;
}
/**
* Checks that the given number is not negative, throwing IAE if it is. The given description
* describes the number in the exception message.
*/
static void checkNotNegative(long n, String description) {
checkArgument(n >= 0, "%s must not be negative: %s", description, n);
}
/** Checks that no element in the given iterable is null, throwing NPE if any is. */
static void checkNoneNull(Iterable<?> objects) {
if (!(objects instanceof ImmutableCollection)) {
for (Object o : objects) {
checkNotNull(o);
}
}
}
private static final int C1 = 0xcc9e2d51;
private static final int C2 = 0x1b873593;
/*
* This method was rewritten in Java from an intermediate step of the Murmur hash function in
* http://code.google.com/p/smhasher/source/browse/trunk/MurmurHash3.cpp, which contained the
* following header:
*
* MurmurHash3 was written by Austin Appleby, and is placed in the public domain. The author
* hereby disclaims copyright to this source code.
*/
static int smearHash(int hashCode) {
return C2 * Integer.rotateLeft(hashCode * C1, 15);
}
private static final int ARRAY_LEN = 8192;
private static final byte[] ZERO_ARRAY = new byte[ARRAY_LEN];
private static final byte[][] NULL_ARRAY = new byte[ARRAY_LEN][];
/** Zeroes all bytes between off (inclusive) and off + len (exclusive) in the given array. */
static void zero(byte[] bytes, int off, int len) {
// this is significantly faster than looping or Arrays.fill (which loops), particularly when
// the length of the slice to be zeroed is <= to ARRAY_LEN (in that case, it's faster by a
// factor of 2)
int remaining = len;
while (remaining > ARRAY_LEN) {
System.arraycopy(ZERO_ARRAY, 0, bytes, off, ARRAY_LEN);
off += ARRAY_LEN;
remaining -= ARRAY_LEN;
}
System.arraycopy(ZERO_ARRAY, 0, bytes, off, remaining);
}
/**
* Clears (sets to null) all blocks between off (inclusive) and off + len (exclusive) in the given
* array.
*/
static void clear(byte[][] blocks, int off, int len) {
// this is significantly faster than looping or Arrays.fill (which loops), particularly when
// the length of the slice to be cleared is <= to ARRAY_LEN (in that case, it's faster by a
// factor of 2)
int remaining = len;
while (remaining > ARRAY_LEN) {
System.arraycopy(NULL_ARRAY, 0, blocks, off, ARRAY_LEN);
off += ARRAY_LEN;
remaining -= ARRAY_LEN;
}
System.arraycopy(NULL_ARRAY, 0, blocks, off, remaining);
}
}
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