// this^e, e < 2^32, doing sqr and mul with "r" (HAC 14.79)
private BigInteger Exponential(long e, IExponential z)
{
if (e > 0xffffffff || e < 1)
{
return(One);
}
var result = new BigInteger();
var result2 = new BigInteger();
var g = z.Convert(this);
var i = NumberOfBits((int)e) - 1;
g.CopyTo(result);
while (--i >= 0)
{
z.SquareTo(result, result2);
if ((e & (1 << i)) > 0)
{
z.MultiplyTo(result2, g, result);
}
else
{
var temp = result;
result = result2;
result2 = temp;
}
}
return(z.Revert(result));
}
// this^e % m (HAC 14.85)
public BigInteger ModuloPower(BigInteger e, BigInteger m)
{
var i = e.BitLength;
var k = 0;
var result = ValueOf(1);
IExponential z = null;
if (i <= 0)
{
return(result);
}
if (i < 18)
{
k = 1;
}
else if (i < 48)
{
k = 3;
}
else if (i < 144)
{
k = 4;
}
else if (i < 768)
{
k = 5;
}
else
{
k = 6;
}
if (i < 8)
{
z = new ClassicExponential(m);
}
else if (m.IsEven)
{
z = new BarrettExponential(m);
}
else
{
z = new MontgomeryExponential(m);
}
// precomputation
var g = new BigInteger[2];
var n = 3;
var k1 = k - 1;
var km = (1 << k) - 1;
g[1] = z.Convert(this);
if (k > 1)
{
var g2 = new BigInteger();
z.SquareTo(g[1], g2);
while (n <= km)
{
if (n + 1 > g.Length)
{
Array.Resize(ref g, n + 1);
}
g[n] = new BigInteger();
z.MultiplyTo(g2, g[n - 2], g[n]);
n += 2;
}
}
var j = e.t - 1;
var isFirstIteration = true;
var result2 = new BigInteger();
i = NumberOfBits(e[j]) - 1;
while (j >= 0)
{
var w = 0;
if (i >= k1)
{
w = (e[j] >> (i - k1)) & km;
}
else
{
w = (e[j] & ((1 << (i + 1)) - 1)) << (k1 - i);
if (j > 0)
{
w |= e[j - 1] >> (DB + i - k1);
}
}
n = k;
while ((w & 1) == 0)
{
w = w >> 1;
n--;
}
if ((i -= n) < 0)
{
i += DB;
j--;
}
if (isFirstIteration) // ret == 1, don't bother squaring or multiplying it
{
g[w].CopyTo(result);
isFirstIteration = false;
}
else
{
while (n > 1)
{
z.SquareTo(result, result2);
z.SquareTo(result2, result);
n -= 2;
}
if (n > 0)
{
z.SquareTo(result, result2);
}
else
{
var temp = result;
result = result2;
result2 = temp;
}
z.MultiplyTo(result2, g[w], result);
}
while (j >= 0 && (e[j] & (1 << i)) == 0)
{
z.SquareTo(result, result2);
var temp = result;
result = result2;
result2 = temp;
if (--i < 0)
{
i = DB - 1;
j--;
}
}
}
return(z.Revert(result));
}
