| // Copyright 2023 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 java.util.Objects; |
| import javax.annotation.Nullable; |
| |
| /** |
| * Helper library for hash codes that generates less garbage than {@link Objects#hash}. |
| * |
| * <p>This uses the same underlying algorithm as the {@link Objects#hash} but explicitly overloads |
| * for different argument counts instead of using varargs. The benefit is that it generates no |
| * garbage. |
| * |
| * <p>{@link Object#hashCode} implementations tend to be garbage hotspots in Bazel, especially with |
| * hashmaps. |
| */ |
| public final class HashCodes { |
| /** |
| * Value to use when composing two hash codes. |
| * |
| * <p>31 is prime so modulo-multiplication is invertible (it spans the full range of values). |
| * Multiplication by 31 also efficient because {@code 31 * x} optimizes down to {@code (x << 5) - |
| * x}. |
| */ |
| public static final int MULTIPLIER = 31; |
| |
| private HashCodes() {} |
| |
| /** Returns the hashCode of a given object if it is non-null and 0 otherwise. */ |
| public static int hashObject(@Nullable Object obj) { |
| return obj == null ? 0 : obj.hashCode(); |
| } |
| |
| public static int hashObjects(@Nullable Object o1, @Nullable Object o2) { |
| int h1 = hashObject(o1); |
| int h2 = hashObject(o2); |
| return h2 + (MULTIPLIER * (h1 + MULTIPLIER)); |
| } |
| |
| public static int hashObjects(@Nullable Object o1, @Nullable Object o2, @Nullable Object o3) { |
| int h1 = hashObject(o1); |
| int h2 = hashObject(o2); |
| int h3 = hashObject(o3); |
| return h3 + MULTIPLIER * (h2 + (MULTIPLIER * (h1 + MULTIPLIER))); |
| } |
| |
| public static int hashObjects( |
| @Nullable Object o1, @Nullable Object o2, @Nullable Object o3, @Nullable Object o4) { |
| int h1 = hashObject(o1); |
| int h2 = hashObject(o2); |
| int h3 = hashObject(o3); |
| int h4 = hashObject(o4); |
| return h4 + MULTIPLIER * (h3 + MULTIPLIER * (h2 + (MULTIPLIER * (h1 + MULTIPLIER)))); |
| } |
| |
| public static int hashObjects( |
| @Nullable Object o1, |
| @Nullable Object o2, |
| @Nullable Object o3, |
| @Nullable Object o4, |
| @Nullable Object o5) { |
| int h1 = hashObject(o1); |
| int h2 = hashObject(o2); |
| int h3 = hashObject(o3); |
| int h4 = hashObject(o4); |
| int h5 = hashObject(o5); |
| return h5 |
| + MULTIPLIER |
| * (h4 + MULTIPLIER * (h3 + MULTIPLIER * (h2 + (MULTIPLIER * (h1 + MULTIPLIER))))); |
| } |
| } |