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The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.4.

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package org.bouncycastle.util;

import org.bouncycastle.math.raw.Bits;

public class Longs
{
    public static long reverse(long i)
    {
        i = Bits.bitPermuteStepSimple(i, 0x5555555555555555L, 1);
        i = Bits.bitPermuteStepSimple(i, 0x3333333333333333L, 2);
        i = Bits.bitPermuteStepSimple(i, 0x0F0F0F0F0F0F0F0FL, 4);
        return reverseBytes(i);
    }

    public static long reverseBytes(long i)
    {
        return rotateLeft(i & 0xFF000000FF000000L,  8) |
               rotateLeft(i & 0x00FF000000FF0000L, 24) |
               rotateLeft(i & 0x0000FF000000FF00L, 40) |
               rotateLeft(i & 0x000000FF000000FFL, 56);
    }

    public static long rotateLeft(long i, int distance)
    {
        return (i << distance) ^ (i >>> -distance);
    }

    public static long rotateRight(long i, int distance)
    {
        return (i >>> distance) ^ (i << -distance);
    }

    public static Long valueOf(long value)
    {
        return new Long(value);
    }
}