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package sun.security.util.math.intpoly;

import java.lang.invoke.MethodHandles;

import java.math.BigInteger;

import java.nio.*;

/**

 * An IntegerFieldModuloP designed for use with the Poly1305 authenticator.

 * The representation uses 5 signed long values.

 */

public class IntegerPolynomial1305 extends IntegerPolynomial {

    protected static final int SUBTRAHEND = 5;

    protected static final int NUM_LIMBS = 5;

    private static final int POWER = 130;

    private static final int BITS_PER_LIMB = 26;

    private static final BigInteger MODULUS

        = TWO.pow(POWER).subtract(BigInteger.valueOf(SUBTRAHEND));

    public IntegerPolynomial1305() {

        super(BITS_PER_LIMB, NUM_LIMBS, 1, MODULUS);

    }

    protected void mult(long[] a, long[] b, long[] r) {

        // Use grade-school multiplication into primitives to avoid the

        // temporary array allocation. This is equivalent to the following

        // code:

        //  long[] c = new long[2 * NUM_LIMBS - 1];

        //  for(int i = 0; i < NUM_LIMBS; i++) {

        //      for(int j - 0; j < NUM_LIMBS; j++) {

        //          c[i + j] += a[i] * b[j]

        //      }

        //  }

        long c0 = (a[0] * b[0]);

        long c1 = (a[0] * b[1]) + (a[1] * b[0]);

        long c2 = (a[0] * b[2]) + (a[1] * b[1]) + (a[2] * b[0]);

        long c3 = (a[0] * b[3]) + (a[1] * b[2]) + (a[2] * b[1]) + (a[3] * b[0]);

        long c4 = (a[0] * b[4]) + (a[1] * b[3]) + (a[2] * b[2]) + (a[3] * b[1]) + (a[4] * b[0]);

        long c5 = (a[1] * b[4]) + (a[2] * b[3]) + (a[3] * b[2]) + (a[4] * b[1]);

        long c6 = (a[2] * b[4]) + (a[3] * b[3]) + (a[4] * b[2]);

        long c7 = (a[3] * b[4]) + (a[4] * b[3]);

        long c8 = (a[4] * b[4]);

        carryReduce(r, c0, c1, c2, c3, c4, c5, c6, c7, c8);

    }

    private void carryReduce(long[] r, long c0, long c1, long c2, long c3,

                             long c4, long c5, long c6, long c7, long c8) {

        //reduce(2, 2)

        r[2] = c2 + (c7 * SUBTRAHEND);

        c3 += (c8 * SUBTRAHEND);

        // carry(3, 2)

        long carry3 = carryValue(c3);

        r[3] = c3 - (carry3 << BITS_PER_LIMB);

        c4 += carry3;

        long carry4 = carryValue(c4);

        r[4] = c4 - (carry4 << BITS_PER_LIMB);

        c5 += carry4;

        // reduce(0, 2)

        r[0] = c0 + (c5 * SUBTRAHEND);

        r[1] = c1 + (c6 * SUBTRAHEND);

        // carry(0, 4)

        carry(r);

    }

    @Override

    protected void square(long[] a, long[] r) {

        // Use grade-school multiplication with a simple squaring optimization.

        // Multiply into primitives to avoid the temporary array allocation.

        // This is equivalent to the following code:

        //  long[] c = new long[2 * NUM_LIMBS - 1];

        //  for(int i = 0; i < NUM_LIMBS; i++) {

        //      c[2 * i] = a[i] * a[i];

        //      for(int j = i + 1; j < NUM_LIMBS; j++) {

        //          c[i + j] += 2 * a[i] * a[j]

        //      }

        //  }

        long c0 = (a[0] * a[0]);

        long c1 = 2 * (a[0] * a[1]);

        long c2 = 2 * (a[0] * a[2]) + (a[1] * a[1]);

        long c3 = 2 * (a[0] * a[3] + a[1] * a[2]);

        long c4 = 2 * (a[0] * a[4] + a[1] * a[3]) + (a[2] * a[2]);

        long c5 = 2 * (a[1] * a[4] + a[2] * a[3]);

        long c6 = 2 * (a[2] * a[4]) + (a[3] * a[3]);

        long c7 = 2 * (a[3] * a[4]);

        long c8 = (a[4] * a[4]);

        carryReduce(r, c0, c1, c2, c3, c4, c5, c6, c7, c8);

    }

    @Override

    protected void encode(ByteBuffer buf, int length, byte highByte,

                          long[] result) {

        if (length == 16) {

            long low = buf.getLong();

            long high = buf.getLong();

            encode(high, low, highByte, result);

        } else {

            super.encode(buf, length, highByte, result);

        }

    }

    protected void encode(long high, long low, byte highByte, long[] result) {

        result[0] = low & 0x3FFFFFFL;

        result[1] = (low >>> 26) & 0x3FFFFFFL;

        result[2] = (low >>> 52) + ((high & 0x3FFFL) << 12);

        result[3] = (high >>> 14) & 0x3FFFFFFL;

        result[4] = (high >>> 40) + (highByte << 24L);

    }

    protected void encode(byte[] v, int offset, int length, byte highByte,

                          long[] result) {

        if (length == 16) {

            ByteBuffer asLongLEBuffer = ByteBuffer.wrap(v, offset, length)

                    .order(ByteOrder.LITTLE_ENDIAN);

            long low = asLongLEBuffer.getLong();

            long high = asLongLEBuffer.getLong();

            encode(high, low, highByte, result);

        } else {

            super.encode(v, offset, length, highByte, result);

        }

    }

    private void modReduceIn(long[] limbs, int index, long x) {

        // this only works when BITS_PER_LIMB * NUM_LIMBS = POWER exactly

        long reducedValue = (x * SUBTRAHEND);

        limbs[index - NUM_LIMBS] += reducedValue;

    }

    @Override

    protected void finalCarryReduceLast(long[] limbs) {

        long carry = limbs[numLimbs - 1] >> bitsPerLimb;

        limbs[numLimbs - 1] -= carry << bitsPerLimb;

        modReduceIn(limbs, numLimbs, carry);

    }

    protected final void modReduce(long[] limbs, int start, int end) {

        for (int i = start; i < end; i++) {

            modReduceIn(limbs, i, limbs[i]);

            limbs[i] = 0;

        }

    }

    protected void modReduce(long[] limbs) {

        modReduce(limbs, NUM_LIMBS, NUM_LIMBS - 1);

    }

    @Override

    protected long carryValue(long x) {

        // This representation has plenty of extra space, so we can afford to

        // do a simplified carry operation that is more time-efficient.

        return x >> BITS_PER_LIMB;

    }

    @Override

    protected void postEncodeCarry(long[] v) {

        // not needed because carry is unsigned

    }

    @Override

    protected void reduce(long[] limbs) {

        long carry3 = carryOut(limbs, 3);

        long new4 = carry3 + limbs[4];

        long carry4 = carryValue(new4);

        limbs[4] = new4 - (carry4 << BITS_PER_LIMB);

        modReduceIn(limbs, 5, carry4);

        carry(limbs);

    }

}