package org.bouncycastle.math.ec.custom.sec;

import java.math.BigInteger;

import org.bouncycastle.math.raw.Interleave;
import org.bouncycastle.math.raw.Nat256;

public class SecT239Field
{
    private static final long M47 = -1L >>> 17;
    private static final long M60 = -1L >>> 4;

    public static void add(long[] x, long[] y, long[] z)
    {
        z[0] = x[0] ^ y[0];
        z[1] = x[1] ^ y[1];
        z[2] = x[2] ^ y[2];
        z[3] = x[3] ^ y[3];
    }

    public static void addExt(long[] xx, long[] yy, long[] zz)
    {
        zz[0] = xx[0] ^ yy[0];
        zz[1] = xx[1] ^ yy[1];
        zz[2] = xx[2] ^ yy[2];
        zz[3] = xx[3] ^ yy[3];
        zz[4] = xx[4] ^ yy[4];
        zz[5] = xx[5] ^ yy[5];
        zz[6] = xx[6] ^ yy[6];
        zz[7] = xx[7] ^ yy[7];
    }

    public static void addOne(long[] x, long[] z)
    {
        z[0] = x[0] ^ 1L;
        z[1] = x[1];
        z[2] = x[2];
        z[3] = x[3];
    }

    public static long[] fromBigInteger(BigInteger x)
    {
        long[] z = Nat256.fromBigInteger64(x);
        reduce17(z, 0);
        return z;
    }

    public static void invert(long[] x, long[] z)
    {
        if (Nat256.isZero64(x))
        {
            throw new IllegalStateException();
        }

        // Itoh-Tsujii inversion

        long[] t0 = Nat256.create64();
        long[] t1 = Nat256.create64();

        square(x, t0);
        multiply(t0, x, t0);
        square(t0, t0);
        multiply(t0, x, t0);
        squareN(t0, 3, t1);
        multiply(t1, t0, t1);
        square(t1, t1);
        multiply(t1, x, t1);
        squareN(t1, 7, t0);
        multiply(t0, t1, t0);
        squareN(t0, 14, t1);
        multiply(t1, t0, t1);
        square(t1, t1);
        multiply(t1, x, t1);
        squareN(t1, 29, t0);
        multiply(t0, t1, t0);
        square(t0, t0);
        multiply(t0, x, t0);
        squareN(t0, 59, t1);
        multiply(t1, t0, t1);
        square(t1, t1);
        multiply(t1, x, t1);
        squareN(t1, 119, t0);
        multiply(t0, t1, t0);
        square(t0, z);
    }

    public static void multiply(long[] x, long[] y, long[] z)
    {
        long[] tt = Nat256.createExt64();
        implMultiply(x, y, tt);
        reduce(tt, z);
    }

    public static void multiplyAddToExt(long[] x, long[] y, long[] zz)
    {
        long[] tt = Nat256.createExt64();
        implMultiply(x, y, tt);
        addExt(zz, tt, zz);
    }

    public static void reduce(long[] xx, long[] z)
    {
        long x0 = xx[0], x1 = xx[1], x2 = xx[2], x3 = xx[3];
        long x4 = xx[4], x5 = xx[5], x6 = xx[6], x7 = xx[7];

        x3 ^= (x7 <<  17);
        x4 ^= (x7 >>> 47);
        x5 ^= (x7 <<  47);
        x6 ^= (x7 >>> 17);

        x2 ^= (x6 <<  17);
        x3 ^= (x6 >>> 47);
        x4 ^= (x6 <<  47);
        x5 ^= (x6 >>> 17);

        x1 ^= (x5 <<  17);
        x2 ^= (x5 >>> 47);
        x3 ^= (x5 <<  47);
        x4 ^= (x5 >>> 17);

        x0 ^= (x4 <<  17);
        x1 ^= (x4 >>> 47);
        x2 ^= (x4 <<  47);
        x3 ^= (x4 >>> 17);

        long t = x3 >>> 47;
        z[0]   = x0 ^ t;
        z[1]   = x1;
        z[2]   = x2 ^ (t << 30);
        z[3]   = x3 & M47;
    }

    public static void reduce17(long[] z, int zOff)
    {
        long z3      = z[zOff + 3], t = z3 >>> 47;
        z[zOff    ] ^= t;
        z[zOff + 2] ^= (t << 30);
        z[zOff + 3]  = z3 & M47;
    }

    public static void square(long[] x, long[] z)
    {
        long[] tt = Nat256.createExt64();
        implSquare(x, tt);
        reduce(tt, z);
    }

    public static void squareAddToExt(long[] x, long[] zz)
    {
        long[] tt = Nat256.createExt64();
        implSquare(x, tt);
        addExt(zz, tt, zz);
    }

    public static void squareN(long[] x, int n, long[] z)
    {
//        assert n > 0;

        long[] tt = Nat256.createExt64();
        implSquare(x, tt);
        reduce(tt, z);

        while (--n > 0)
        {
            implSquare(z, tt);
            reduce(tt, z);
        }
    }

    protected static void implCompactExt(long[] zz)
    {
        long z0 = zz[0], z1 = zz[1], z2 = zz[2], z3 = zz[3], z4 = zz[4], z5 = zz[5], z6 = zz[6], z7 = zz[7];
        zz[0] =  z0         ^ (z1 << 60);
        zz[1] = (z1 >>>  4) ^ (z2 << 56);
        zz[2] = (z2 >>>  8) ^ (z3 << 52);
        zz[3] = (z3 >>> 12) ^ (z4 << 48);
        zz[4] = (z4 >>> 16) ^ (z5 << 44);
        zz[5] = (z5 >>> 20) ^ (z6 << 40);
        zz[6] = (z6 >>> 24) ^ (z7 << 36);
        zz[7] = (z7 >>> 28);
    }

    protected static void implExpand(long[] x, long[] z)
    {
        long x0 = x[0], x1 = x[1], x2 = x[2], x3 = x[3];
        z[0] = x0 & M60;
        z[1] = ((x0 >>> 60) ^ (x1 <<  4)) & M60;
        z[2] = ((x1 >>> 56) ^ (x2 <<  8)) & M60;
        z[3] = ((x2 >>> 52) ^ (x3 << 12));
    }

    protected static void implMultiply(long[] x, long[] y, long[] zz)
    {
        /*
         * "Two-level seven-way recursion" as described in "Batch binary Edwards", Daniel J. Bernstein.
         */

        long[] f = new long[4], g = new long[4];
        implExpand(x, f);
        implExpand(y, g);

        implMulwAcc(f[0], g[0], zz, 0);
        implMulwAcc(f[1], g[1], zz, 1);
        implMulwAcc(f[2], g[2], zz, 2);
        implMulwAcc(f[3], g[3], zz, 3);

        // U *= (1 - t^n)
        for (int i = 5; i > 0; --i)
        {
            zz[i] ^= zz[i - 1];
        }

        implMulwAcc(f[0] ^ f[1], g[0] ^ g[1], zz, 1);
        implMulwAcc(f[2] ^ f[3], g[2] ^ g[3], zz, 3);

        // V *= (1 - t^2n)
        for (int i = 7; i > 1; --i)
        {
            zz[i] ^= zz[i - 2];
        }

        // Double-length recursion
        {
            long c0 = f[0] ^ f[2], c1 = f[1] ^ f[3];
            long d0 = g[0] ^ g[2], d1 = g[1] ^ g[3];
            implMulwAcc(c0 ^ c1, d0 ^ d1, zz, 3);
            long[] t = new long[3];
            implMulwAcc(c0, d0, t, 0);
            implMulwAcc(c1, d1, t, 1);
            long t0 = t[0], t1 = t[1], t2 = t[2];
            zz[2] ^= t0;
            zz[3] ^= t0 ^ t1;
            zz[4] ^= t2 ^ t1;
            zz[5] ^= t2;
        }

        implCompactExt(zz);
    }

    protected static void implMulwAcc(long x, long y, long[] z, int zOff)
    {
//        assert x >>> 60 == 0;
//        assert y >>> 60 == 0;

        long[] u = new long[8];
//      u[0] = 0;
        u[1] = y;
        u[2] = u[1] << 1;
        u[3] = u[2] ^  y;
        u[4] = u[2] << 1;
        u[5] = u[4] ^  y;
        u[6] = u[3] << 1;
        u[7] = u[6] ^  y;

        int j = (int)x;
        long g, h = 0, l = u[j & 7]
                         ^ (u[(j >>> 3) & 7] << 3);
        int k = 54;
        do
        {
            j  = (int)(x >>> k);
            g  = u[j & 7]
               ^ u[(j >>> 3) & 7] << 3;
            l ^= (g <<   k);
            h ^= (g >>> -k);
        }
        while ((k -= 6) > 0);

        h ^= ((x & 0x0820820820820820L) & ((y << 4) >> 63)) >>> 5;

//        assert h >>> 55 == 0;

        z[zOff    ] ^= l & M60;
        z[zOff + 1] ^= (l >>> 60) ^ (h << 4);
    }

    protected static void implSquare(long[] x, long[] zz)
    {
        Interleave.expand64To128(x[0], zz, 0);
        Interleave.expand64To128(x[1], zz, 2);
        Interleave.expand64To128(x[2], zz, 4);

        long x3 = x[3];
        zz[6] = Interleave.expand32to64((int)x3);
        zz[7] = Interleave.expand16to32((int)(x3 >>> 32)) & 0xFFFFFFFFL;
    }
}
