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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 1.5 to JDK 1.7. Note: this package includes the IDEA and NTRU encryption algorithms.
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package org.bouncycastle.math.raw;

public class Interleave
{
    private static final long M32 = 0x55555555L;
    private static final long M64 = 0x5555555555555555L;
    private static final long M64R = 0xAAAAAAAAAAAAAAAAL;

    /*
     * This expands 8 bit indices into 16 bit contents (high bit 14), by inserting 0s between bits.
     * In a binary field, this operation is the same as squaring an 8 bit number.
     * 
     * NOTE: All entries are positive so sign-extension is not an issue.
     */
//    private static final short[] INTERLEAVE2_TABLE = new short[]
//    {
//        0x0000, 0x0001, 0x0004, 0x0005, 0x0010, 0x0011, 0x0014, 0x0015,
//        0x0040, 0x0041, 0x0044, 0x0045, 0x0050, 0x0051, 0x0054, 0x0055,
//        0x0100, 0x0101, 0x0104, 0x0105, 0x0110, 0x0111, 0x0114, 0x0115,
//        0x0140, 0x0141, 0x0144, 0x0145, 0x0150, 0x0151, 0x0154, 0x0155,
//        0x0400, 0x0401, 0x0404, 0x0405, 0x0410, 0x0411, 0x0414, 0x0415,
//        0x0440, 0x0441, 0x0444, 0x0445, 0x0450, 0x0451, 0x0454, 0x0455,
//        0x0500, 0x0501, 0x0504, 0x0505, 0x0510, 0x0511, 0x0514, 0x0515,
//        0x0540, 0x0541, 0x0544, 0x0545, 0x0550, 0x0551, 0x0554, 0x0555,
//        0x1000, 0x1001, 0x1004, 0x1005, 0x1010, 0x1011, 0x1014, 0x1015,
//        0x1040, 0x1041, 0x1044, 0x1045, 0x1050, 0x1051, 0x1054, 0x1055,
//        0x1100, 0x1101, 0x1104, 0x1105, 0x1110, 0x1111, 0x1114, 0x1115,
//        0x1140, 0x1141, 0x1144, 0x1145, 0x1150, 0x1151, 0x1154, 0x1155,
//        0x1400, 0x1401, 0x1404, 0x1405, 0x1410, 0x1411, 0x1414, 0x1415,
//        0x1440, 0x1441, 0x1444, 0x1445, 0x1450, 0x1451, 0x1454, 0x1455,
//        0x1500, 0x1501, 0x1504, 0x1505, 0x1510, 0x1511, 0x1514, 0x1515,
//        0x1540, 0x1541, 0x1544, 0x1545, 0x1550, 0x1551, 0x1554, 0x1555,
//        0x4000, 0x4001, 0x4004, 0x4005, 0x4010, 0x4011, 0x4014, 0x4015,
//        0x4040, 0x4041, 0x4044, 0x4045, 0x4050, 0x4051, 0x4054, 0x4055,
//        0x4100, 0x4101, 0x4104, 0x4105, 0x4110, 0x4111, 0x4114, 0x4115,
//        0x4140, 0x4141, 0x4144, 0x4145, 0x4150, 0x4151, 0x4154, 0x4155,
//        0x4400, 0x4401, 0x4404, 0x4405, 0x4410, 0x4411, 0x4414, 0x4415,
//        0x4440, 0x4441, 0x4444, 0x4445, 0x4450, 0x4451, 0x4454, 0x4455,
//        0x4500, 0x4501, 0x4504, 0x4505, 0x4510, 0x4511, 0x4514, 0x4515,
//        0x4540, 0x4541, 0x4544, 0x4545, 0x4550, 0x4551, 0x4554, 0x4555,
//        0x5000, 0x5001, 0x5004, 0x5005, 0x5010, 0x5011, 0x5014, 0x5015,
//        0x5040, 0x5041, 0x5044, 0x5045, 0x5050, 0x5051, 0x5054, 0x5055,
//        0x5100, 0x5101, 0x5104, 0x5105, 0x5110, 0x5111, 0x5114, 0x5115,
//        0x5140, 0x5141, 0x5144, 0x5145, 0x5150, 0x5151, 0x5154, 0x5155,
//        0x5400, 0x5401, 0x5404, 0x5405, 0x5410, 0x5411, 0x5414, 0x5415,
//        0x5440, 0x5441, 0x5444, 0x5445, 0x5450, 0x5451, 0x5454, 0x5455,
//        0x5500, 0x5501, 0x5504, 0x5505, 0x5510, 0x5511, 0x5514, 0x5515,
//        0x5540, 0x5541, 0x5544, 0x5545, 0x5550, 0x5551, 0x5554, 0x5555
//    };

    public static int expand8to16(int x)
    {
        x &= 0xFF;
        x  = (x | (x << 4)) & 0x0F0F;
        x  = (x | (x << 2)) & 0x3333;
        x  = (x | (x << 1)) & 0x5555;
        return x;
    }

    public static int expand16to32(int x)
    {
        x &= 0xFFFF;
        x  = (x | (x << 8)) & 0x00FF00FF;
        x  = (x | (x << 4)) & 0x0F0F0F0F;
        x  = (x | (x << 2)) & 0x33333333;
        x  = (x | (x << 1)) & 0x55555555;
        return x;
    }

    public static long expand32to64(int x)
    {
        // "shuffle" low half to even bits and high half to odd bits
        int t;
        t = (x ^ (x >>>  8)) & 0x0000FF00; x ^= (t ^ (t <<  8));
        t = (x ^ (x >>>  4)) & 0x00F000F0; x ^= (t ^ (t <<  4));
        t = (x ^ (x >>>  2)) & 0x0C0C0C0C; x ^= (t ^ (t <<  2));
        t = (x ^ (x >>>  1)) & 0x22222222; x ^= (t ^ (t <<  1));

        return ((x >>> 1) & M32) << 32 | (x & M32);
    }

    public static void expand64To128(long x, long[] z, int zOff)
    {
        // "shuffle" low half to even bits and high half to odd bits
        long t;
        t = (x ^ (x >>> 16)) & 0x00000000FFFF0000L; x ^= (t ^ (t << 16));
        t = (x ^ (x >>>  8)) & 0x0000FF000000FF00L; x ^= (t ^ (t <<  8));
        t = (x ^ (x >>>  4)) & 0x00F000F000F000F0L; x ^= (t ^ (t <<  4));
        t = (x ^ (x >>>  2)) & 0x0C0C0C0C0C0C0C0CL; x ^= (t ^ (t <<  2));
        t = (x ^ (x >>>  1)) & 0x2222222222222222L; x ^= (t ^ (t <<  1));

        z[zOff    ] = (x      ) & M64;
        z[zOff + 1] = (x >>> 1) & M64;
    }

    public static void expand64To128Rev(long x, long[] z, int zOff)
    {
        // "shuffle" low half to even bits and high half to odd bits
        long t;
        t = (x ^ (x >>> 16)) & 0x00000000FFFF0000L; x ^= (t ^ (t << 16));
        t = (x ^ (x >>>  8)) & 0x0000FF000000FF00L; x ^= (t ^ (t <<  8));
        t = (x ^ (x >>>  4)) & 0x00F000F000F000F0L; x ^= (t ^ (t <<  4));
        t = (x ^ (x >>>  2)) & 0x0C0C0C0C0C0C0C0CL; x ^= (t ^ (t <<  2));
        t = (x ^ (x >>>  1)) & 0x2222222222222222L; x ^= (t ^ (t <<  1));

        z[zOff    ] = (x     ) & M64R;
        z[zOff + 1] = (x << 1) & M64R;
    }

    public static long unshuffle(long x)
    {
        // "unshuffle" even bits to low half and odd bits to high half
        long t;
        t = (x ^ (x >>>  1)) & 0x2222222222222222L; x ^= (t ^ (t <<  1));
        t = (x ^ (x >>>  2)) & 0x0C0C0C0C0C0C0C0CL; x ^= (t ^ (t <<  2));
        t = (x ^ (x >>>  4)) & 0x00F000F000F000F0L; x ^= (t ^ (t <<  4));
        t = (x ^ (x >>>  8)) & 0x0000FF000000FF00L; x ^= (t ^ (t <<  8));
        t = (x ^ (x >>> 16)) & 0x00000000FFFF0000L; x ^= (t ^ (t << 16));
        return x;
    }
}