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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 Integers
{
    public static final int BYTES = 4;
    public static final int SIZE = 32;

    private static final byte[] DEBRUIJN_TZ = {
        0x1F, 0x00, 0x1B, 0x01, 0x1C, 0x0D, 0x17, 0x02, 0x1D, 0x15, 0x13, 0x0E, 0x18, 0x10, 0x03, 0x07,
        0x1E, 0x1A, 0x0C, 0x16, 0x14, 0x12, 0x0F, 0x06, 0x19, 0x0B, 0x11, 0x05, 0x0A, 0x04, 0x09, 0x08 };

    public static int bitCount(int i)
    {
        i -= (i >>> 1) & 0x55555555;
        i = (i & 0x33333333) + ((i >>> 2) & 0x33333333);
        i = (i + (i >>> 4)) & 0x0f0f0f0f;
        i += (i >>> 8);
        i += (i >>> 16);
        i &= 0x3f;
        return i;
    }

    public static int highestOneBit(int i)
    {
        i |= (i >>  1);
        i |= (i >>  2);
        i |= (i >>  4);
        i |= (i >>  8);
        i |= (i >> 16);
        return i - (i >>> 1);
    }

    public static int lowestOneBit(int i)
    {
        return i & -i;
    }

    public static int numberOfLeadingZeros(int i)
    {
        if (i <= 0)
        {
            return (~i >>> (31 - 5)) & (1 << 5);
        }

        int n = 1;
        if (0 == (i >>> 16)) { n += 16; i <<= 16; }
        if (0 == (i >>> 24)) { n +=  8; i <<=  8; }
        if (0 == (i >>> 28)) { n +=  4; i <<=  4; }
        if (0 == (i >>> 30)) { n +=  2; i <<=  2; }
        n -= (i >>> 31);
        return n;
    }

    public static int numberOfTrailingZeros(int i)
    {
        int n = DEBRUIJN_TZ[((i & -i) * 0x0EF96A62) >>> 27];
        int m = (((i & 0xFFFF) | (i >>> 16)) - 1) >> 31;
        return n - m;
    }

    public static int reverse(int i)
    {
        i = Bits.bitPermuteStepSimple(i, 0x55555555, 1);
        i = Bits.bitPermuteStepSimple(i, 0x33333333, 2);
        i = Bits.bitPermuteStepSimple(i, 0x0F0F0F0F, 4);
        return reverseBytes(i);
    }

    public static int reverseBytes(int i)
    {
        return rotateLeft(i & 0xFF00FF00,  8) |
               rotateLeft(i & 0x00FF00FF, 24);
    }

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

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

    public static Integer valueOf(int value)
    {
        return new Integer(value);
    }
}