static void Div(
Digits numer
, Digit den
, Reciprocal recip
, Digits q
, int n
, Digits r
)
{
Digit carry = 0;
int nLeft = n;
if (nLeft > 0 && numer[nLeft - 1] < den)
{
nLeft--;
carry = numer[nLeft];
if (q != null)
{
q[nLeft] = 0;
}
}
if (recip == null && nLeft < 2)
{
for (int i = nLeft; i-- != 0;)
{
Digit qest = 0;
Digit2.Div((UInt64)carry << Digit.BitN | numer[i]
, den
, out qest
, out carry);
if (q != null)
{
q[i] = qest;
}
}
}
else
{
if (recip == null)
{
recip = new Reciprocal();
DivPrecondition(new Digits(new Digit[] { den }), 1, recip);
}
for (int i = nLeft; i-- != 0;)
{
Digit qest = 0;
Digit2.Div((UInt64)carry << Digit.BitN | numer[i]
, den
, recip
, out qest
, out carry);
if (q != null)
{
q[i] = qest;
}
}
}
r[0] = carry;
}
DivPrecondition(Digits denom, int denomN, Reciprocal recip)
{
if (denom == null)
{
throw new ArgumentNullException();
}
if (denomN == 0 || denom[denomN - 1] == 0)
{
throw new ArgumentException();
}
int recipBitShift = Digit.BitN - Digit.SigBitN(denom[denomN - 1]);
Digit dlead2 = denom[denomN - 1]
, dlead1 = denomN >= 2 ? denom[denomN - 2] : 0
, dlead0 = denomN >= 3 ? denom[denomN - 3] : 0
, dShiftHi = dlead2 << recipBitShift
| dlead1 >> 1 >> Digit.BitN - 1 - recipBitShift
, dShiftLo = dlead1 << recipBitShift
| dlead0 >> 1 >> Digit.BitN - 1 - recipBitShift;
Digit recipMpy, r;
Digit2.Div((UInt64)(Digit.MaxValue - dShiftHi) << Digit.BitN
| Digit.MaxValue - dShiftLo
, dShiftHi
, out recipMpy
, out r);
if (Digit2.Hi((UInt64)recipMpy * dShiftLo) > r)
{
recipMpy -= 1;
}
r = (Digit.MaxValue >> recipBitShift) - denom[denomN - 1];
for (int id = denomN; id-- != 0 && r < recipMpy;)
{
UInt64 test1 = (UInt64)r << Digit.BitN
| Digit.MaxValue - (id > 0 ? denom[id - 1] : 0)
, test2 = (UInt64)recipMpy * denom[id];
if (test2 > test1)
{
recipMpy -= 1; break;
}
test1 = test1 - test2;
r = Digit2.Lo(test1);
if (Digit2.Hi(test1) != 0)
{
break;
}
}
recip._shiftBitN = recipBitShift;
recip._multiplier = recipMpy;
}