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Client library for working with the NATS messaging system.

There is a newer version: 2.20.5

// Copyright 2020 The NATS Authors
// 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 io.nats.client.support;

import java.nio.ByteBuffer;
import java.security.SecureRandom;
import java.util.Random;

public abstract class RandomUtils {
    private RandomUtils() {}  /* ensures cannot be constructed */

    public static final SecureRandom SRAND = new SecureRandom();
    public static final Random PRAND = new Random(bytesToLong(SRAND.generateSeed(8))); // seed with 8 bytes (64 bits)

    public static long nextLong(Random rng, long maxValue) {
        // error checking and 2^x checking removed for simplicity.
        long bits;
        long val;
        do {
            bits = (rng.nextLong() << 1) >>> 1;
            val = bits % maxValue;
        } while (bits - val + (maxValue - 1) < 0L);
        return val;
    }

    public static long bytesToLong(byte[] bytes) {
        ByteBuffer buffer = ByteBuffer.allocate(Long.SIZE);
        buffer.put(bytes);
        buffer.flip();// need flip
        return buffer.getLong();
    }
}