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Add TODOs for divisor metadata caching

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Marek Lemańczyk committed 2025-10-01 22:52:21 +02:00
1 parent 513fc7acb0
commit 36d316d19c
53 files changed
+929 -393
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PerfectNumbers.Core/Cpu/MersenneNumberIncrementalCpuTester.cs
+35 -23
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@@ -39,29 +39,41 @@ public class MersenneNumberIncrementalCpuTester(GpuKernelType kernelType)
if (shouldCheck)
{
if (_kernelType == GpuKernelType.Pow2Mod)
{
reject = exponent.PowModWithCycle(q, qCycle) == UInt128.One;
}
else
{
phi = q - one;
reject = false;
if (phi <= ulong.MaxValue)
{
phi64 = (ulong)phi;
if (phi64.PowModWithCycle(q, qCycle) == one)
{
halfPow = (phi64 >> 1).PowModWithCycle(q, qCycle) - one;
if (halfPow.BinaryGcd(q) == one)
{
div = phi64.FastDiv64(exponent, divMul);
divPow = div.PowModWithCycle(q, qCycle) - one;
if (divPow.BinaryGcd(q) == one)
{
reject = true;
}
}
if (_kernelType == GpuKernelType.Pow2Mod)
{
// TODO: Swap this PowModWithCycle call for the ProcessEightBitWindows helper once
// the scalar implementation lands so CPU pow2mod scans match the GPU speedups
// captured in GpuPow2ModBenchmarks.
reject = exponent.PowModWithCycle(q, qCycle) == UInt128.One;
}
else
{
phi = q - one;
reject = false;
if (phi <= ulong.MaxValue)
{
phi64 = (ulong)phi;
// TODO: Route the phi-based powmods through the upcoming windowed helper to
// avoid the current square-and-multiply cost highlighted in the Pow2 bench
// suite when scanning large divisors.
if (phi64.PowModWithCycle(q, qCycle) == one)
{
// TODO: Once the windowed pow2 helper is available expose a version
// that reuses cached windows here instead of recomputing via the slow
// bit ladder for every divisor.
halfPow = (phi64 >> 1).PowModWithCycle(q, qCycle) - one;
if (halfPow.BinaryGcd(q) == one)
{
div = phi64.FastDiv64(exponent, divMul);
// TODO: Replace this divisor powmod with the shared windowed
// implementation so each candidate uses the benchmarked fast
// path instead of the current per-bit multiply chain.
divPow = div.PowModWithCycle(q, qCycle) - one;
if (divPow.BinaryGcd(q) == one)
{
reject = true;
}
}
}
}
}