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using System;
using System.Diagnostics;
namespace Org.BouncyCastle.Math.EC.Custom.Sec
{
internal class SecP521R1Field
{
// 2^521 - 1
internal static readonly uint[] P = new uint[]{ 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF,
0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0x1FF };
private const int P16 = 0x1FF;
public static void Add(uint[] x, uint[] y, uint[] z)
{
uint c = Nat.Add(16, x, y, z) + x[16] + y[16];
if (c > P16 || (c == P16 && Nat.Eq(16, z, P)))
{
c += Nat.Inc(16, z, 0);
c &= P16;
}
z[16] = c;
}
public static void AddOne(uint[] x, uint[] z)
{
Array.Copy(x, 0, z, 0, 16);
uint c = Nat.Inc(16, z, 0) + z[16];
if (c > P16 || (c == P16 && Nat.Eq(16, z, P)))
{
c += Nat.Inc(16, z, 0);
c &= P16;
}
z[16] = c;
}
public static uint[] FromBigInteger(BigInteger x)
{
uint[] z = Nat.FromBigInteger(521, x);
if (Nat.Eq(17, z, P))
{
Nat.Zero(17, z);
}
return z;
}
public static void Half(uint[] x, uint[] z)
{
uint c0 = x[0] & 1, x16 = x[16], c512 = x16 & 1;
Nat.ShiftDownBit(16, x, c512, z);
z[16] = (x16 >> 1) | (c0 << 8);
}
public static void Multiply(uint[] x, uint[] y, uint[] z)
{
uint[] tt = Nat.Create(34);
Nat.Mul(17, x, y, tt);
Reduce(tt, z);
}
public static void Negate(uint[] x, uint[] z)
{
if (Nat.IsZero(17, x))
{
Nat.Zero(17, z);
}
else
{
Nat.Sub(17, P, x, z);
}
}
public static void Reduce(uint[] xx, uint[] z)
{
Debug.Assert(xx[33] == 0);
Debug.Assert(xx[32] >> 18 == 0);
uint xx32 = xx[32];
uint c = Nat.ShiftDownBitsExt(16, xx, 16, 9, xx32, z) >> 23;
c += xx32 >> 9;
c += Nat.Add(16, z, xx, z);
if (c > P16 || (c == P16 && Nat.Eq(16, z, P)))
{
c += Nat.Inc(16, z, 0);
c &= P16;
}
z[16] = c;
}
public static void Reduce23(uint[] z)
{
uint z16 = z[16];
uint c = Nat.AddWord(16, z16 >> 9, z) + (z16 & P16);
if (c > P16 || (c == P16 && Nat.Eq(16, z, P)))
{
c += Nat.Inc(16, z, 0);
c &= P16;
}
z[16] = c;
}
public static void Square(uint[] x, uint[] z)
{
uint[] tt = Nat.Create(34);
Nat.Square(17, x, tt);
Reduce(tt, z);
}
public static void SquareN(uint[] x, int n, uint[] z)
{
Debug.Assert(n > 0);
uint[] tt = Nat.Create(34);
Nat.Square(17, x, tt);
Reduce(tt, z);
while (--n > 0)
{
Nat.Square(17, z, tt);
Reduce(tt, z);
}
}
public static void Subtract(uint[] x, uint[] y, uint[] z)
{
int c = Nat.Sub(16, x, y, z) + (int)(x[16] - y[16]);
if (c < 0)
{
c += Nat.Dec(16, z, 0);
c &= P16;
}
z[16] = (uint)c;
}
public static void Twice(uint[] x, uint[] z)
{
uint c = Nat.ShiftUpBit(16, x, 0, z) | (x[16] << 1);
if (c > P16 || (c == P16 && Nat.Eq(16, z, P)))
{
c += Nat.Inc(16, z, 0);
c &= P16;
}
z[16] = c;
}
}
}
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