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// Copyright 2018 The Bazel Authors. All rights reserved.
//
// 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.devtools.build.lib.util;
import com.google.common.annotations.VisibleForTesting;
import java.math.BigInteger;
import javax.annotation.Nullable;
/** Utility class for fingerprint composition. */
public final class BigIntegerFingerprintUtils {
private static final int BITS = 128;
public static final int BYTES = BITS / 8;
private static final BigInteger UINT128_LIMIT = BigInteger.ONE.shiftLeft(BITS);
@VisibleForTesting public static final int RELATIVE_PRIME_INT = 31;
private static final BigInteger RELATIVE_PRIME = BigInteger.valueOf(RELATIVE_PRIME_INT);
private BigIntegerFingerprintUtils() {}
public static BigInteger compose(BigInteger v1, BigInteger v2) {
return v1.add(v2).mod(UINT128_LIMIT);
}
/**
* Unordered, nullable composition.
*
* <p>null is absorbing and is used to convey errors and unavailability
*/
@Nullable
public static BigInteger composeNullable(@Nullable BigInteger v1, @Nullable BigInteger v2) {
if (v1 == null || v2 == null) {
return null;
}
return compose(v1, v2);
}
@Nullable
public static BigInteger composeOrderedNullable(
@Nullable BigInteger accumulator, @Nullable BigInteger v) {
if (accumulator == null || v == null) {
return null;
}
return compose(accumulator.multiply(RELATIVE_PRIME).mod(UINT128_LIMIT), v);
}
}