private static ulong[] Convolve <TMod>(ReadOnlySpan <long> a, ReadOnlySpan <long> b)
where TMod : struct, IFftMod
{
int z = 1 << CeilPow2(a.Length + b.Length - 1);
var aTemp = new FftModInt <TMod> [z];
for (int i = 0; i < a.Length; i++)
{
aTemp[i] = new FftModInt <TMod>(a[i]);
}
var bTemp = new FftModInt <TMod> [z];
for (int i = 0; i < b.Length; i++)
{
bTemp[i] = new FftModInt <TMod>(b[i]);
}
var c = Convolve <TMod>(aTemp, bTemp, a.Length, b.Length, z);
var result = new ulong[c.Length];
for (int i = 0; i < result.Length; i++)
{
result[i] = (ulong)c[i].Value;
}
return(result);
}
private static Span <FftModInt <TMod> > Convolve <TMod>(Span <FftModInt <TMod> > a, Span <FftModInt <TMod> > b, int n, int m, int z)
where TMod : struct, IFftMod
{
FftModInt <TMod> .Butterfly(a);
FftModInt <TMod> .Butterfly(b);
for (int i = 0; i < a.Length; i++)
{
a[i] *= b[i];
}
FftModInt <TMod> .ButterflyInv(a);
var result = a[0..(n + m - 1)];
