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using System;
using System.Diagnostics;
using Org.BouncyCastle.Crypto.Utilities;
using Org.BouncyCastle.Security;
using Org.BouncyCastle.Utilities;
namespace Org.BouncyCastle.Math.Raw
{
internal abstract class Mod
{
private static readonly SecureRandom RandomSource = new SecureRandom();
public static void Invert(uint[] p, uint[] x, uint[] z)
{
int len = p.Length;
if (Nat.IsZero(len, x))
throw new ArgumentException("cannot be 0", "x");
if (Nat.IsOne(len, x))
{
Array.Copy(x, 0, z, 0, len);
return;
}
uint[] u = Nat.Copy(len, x);
uint[] a = Nat.Create(len);
a[0] = 1;
int ac = 0;
if ((u[0] & 1) == 0)
{
InversionStep(p, u, len, a, ref ac);
}
if (Nat.IsOne(len, u))
{
InversionResult(p, ac, a, z);
return;
}
uint[] v = Nat.Copy(len, p);
uint[] b = Nat.Create(len);
int bc = 0;
int uvLen = len;
for (;;)
{
while (u[uvLen - 1] == 0 && v[uvLen - 1] == 0)
{
--uvLen;
}
if (Nat.Gte(len, u, v))
{
Nat.SubFrom(len, v, u);
Debug.Assert((u[0] & 1) == 0);
ac += Nat.SubFrom(len, b, a) - bc;
InversionStep(p, u, uvLen, a, ref ac);
if (Nat.IsOne(len, u))
{
InversionResult(p, ac, a, z);
return;
}
}
else
{
Nat.SubFrom(len, u, v);
Debug.Assert((v[0] & 1) == 0);
bc += Nat.SubFrom(len, a, b) - ac;
InversionStep(p, v, uvLen, b, ref bc);
if (Nat.IsOne(len, v))
{
InversionResult(p, bc, b, z);
return;
}
}
}
}
public static uint[] Random(uint[] p)
{
int len = p.Length;
uint[] s = Nat.Create(len);
uint m = p[len - 1];
m |= m >> 1;
m |= m >> 2;
m |= m >> 4;
m |= m >> 8;
m |= m >> 16;
do
{
byte[] bytes = new byte[len << 2];
RandomSource.NextBytes(bytes);
Pack.BE_To_UInt32(bytes, 0, s);
s[len - 1] &= m;
}
while (Nat.Gte(len, s, p));
return s;
}
public static void Add(uint[] p, uint[] x, uint[] y, uint[] z)
{
int len = p.Length;
uint c = Nat.Add(len, x, y, z);
if (c != 0)
{
Nat.SubFrom(len, p, z);
}
}
public static void Subtract(uint[] p, uint[] x, uint[] y, uint[] z)
{
int len = p.Length;
int c = Nat.Sub(len, x, y, z);
if (c != 0)
{
Nat.AddTo(len, p, z);
}
}
private static void InversionResult(uint[] p, int ac, uint[] a, uint[] z)
{
if (ac < 0)
{
Nat.Add(p.Length, a, p, z);
}
else
{
Array.Copy(a, 0, z, 0, p.Length);
}
}
private static void InversionStep(uint[] p, uint[] u, int uLen, uint[] x, ref int xc)
{
int len = p.Length;
int count = 0;
while (u[0] == 0)
{
Nat.ShiftDownWord(uLen, u, 0);
count += 32;
}
{
int zeroes = GetTrailingZeroes(u[0]);
if (zeroes > 0)
{
Nat.ShiftDownBits(uLen, u, zeroes, 0);
count += zeroes;
}
}
for (int i = 0; i < count; ++i)
{
if ((x[0] & 1) != 0)
{
if (xc < 0)
{
xc += (int)Nat.AddTo(len, p, x);
}
else
{
xc += Nat.SubFrom(len, p, x);
}
}
Debug.Assert(xc == 0 || xc == -1);
Nat.ShiftDownBit(len, x, (uint)xc);
}
}
private static int GetTrailingZeroes(uint x)
{
Debug.Assert(x != 0);
int count = 0;
while ((x & 1) == 0)
{
x >>= 1;
++count;
}
return count;
}
}
}
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