private static void ScalarMultBase(byte[] k, PointExt r)
{
Precompute();
PointSetNeutral(r);
uint[] n = new uint[ScalarUints + 1];
DecodeScalar(k, 0, n);
// Recode the scalar into signed-digit form
{
n[ScalarUints] = 4U + Nat.CAdd(ScalarUints, ~(int)n[0] & 1, n, L, n);
uint c = Nat.ShiftDownBit(n.Length, n, 0);
Debug.Assert(c == (1U << 31));
}
PointPrecomp p = new PointPrecomp();
int cOff = PrecompSpacing - 1;
for (;;)
{
int tPos = cOff;
for (int b = 0; b < PrecompBlocks; ++b)
{
uint w = 0;
for (int t = 0; t < PrecompTeeth; ++t)
{
uint tBit = n[tPos >> 5] >> (tPos & 0x1F);
w &= ~(1U << t);
w ^= (tBit << t);
tPos += PrecompSpacing;
}
int sign = (int)(w >> (PrecompTeeth - 1)) & 1;
int abs = ((int)w ^ -sign) & PrecompMask;
Debug.Assert(sign == 0 || sign == 1);
Debug.Assert(0 <= abs && abs < PrecompPoints);
PointLookup(b, abs, p);
X448Field.CNegate(sign, p.x);
PointAddPrecomp(p, r);
}
if (--cOff < 0)
{
break;
}
PointDouble(r);
}
}