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);
}
}
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;
}
}
}
}