ConstantTimeUtils.java — netty Source File

Source Code

/*
 * Copyright 2016 The Netty Project
 *
 * The Netty Project licenses this file to you 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:
 *
 *   https://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 io.netty.util.internal;

public final class ConstantTimeUtils {
    private ConstantTimeUtils() { }

    /**
     * Compare two {@code int}s without leaking timing information.
     * <p>
     * The {@code int} return type is intentional and is designed to allow cascading of constant time operations:
     * <pre>
     *     int l1 = 1;
     *     int l2 = 1;
     *     int l3 = 1;
     *     int l4 = 500;
     *     boolean equals = (equalsConstantTime(l1, l2) & equalsConstantTime(l3, l4)) != 0;
     * </pre>
     * @param x the first value.
     * @param y the second value.
     * @return {@code 0} if not equal. {@code 1} if equal.
     */
    public static int equalsConstantTime(int x, int y) {
        int z = ~(x ^ y);
        z &= z >> 16;
        z &= z >> 8;
        z &= z >> 4;
        z &= z >> 2;
        z &= z >> 1;
        return z & 1;
    }

    /**
     * Compare two {@code longs}s without leaking timing information.
     * <p>
     * The {@code int} return type is intentional and is designed to allow cascading of constant time operations:
     * <pre>
     *     long l1 = 1;
     *     long l2 = 1;
     *     long l3 = 1;
     *     long l4 = 500;
     *     boolean equals = (equalsConstantTime(l1, l2) & equalsConstantTime(l3, l4)) != 0;
     * </pre>
     * @param x the first value.
     * @param y the second value.
     * @return {@code 0} if not equal. {@code 1} if equal.
     */
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