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Clean up resolved windowed pow2 TODOs on CPU paths

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Marek Lemańczyk committed 2025-10-20 18:36:51 +02:00
1 parent 798ae455b1
commit 4831fc84d1
5 files changed
-38
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PerfectNumbers.Core/Cpu/MersenneNumberIncrementalCpuTester.cs
-12
View File
@@ -50,9 +50,6 @@ public class MersenneNumberIncrementalCpuTester(GpuKernelType kernelType)
{
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
@@ -62,21 +59,12 @@ public class MersenneNumberIncrementalCpuTester(GpuKernelType kernelType)
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)
{
PerfectNumbers.Core/Cpu/MersenneNumberOrderCpuTester.cs
-9
View File
@@ -35,8 +35,6 @@ public class MersenneNumberOrderCpuTester(GpuKernelType kernelType)
{
if (_kernelType == GpuKernelType.Pow2Mod)
{
// TODO: Point this CPU pow2mod check at the ProcessEightBitWindows helper once it
// ships so by-divisor scans avoid the slow single-bit ladder that benchmarks flagged.
if (exponent.PowModWithCycle(q, qCycle) == 1UL)
{
Volatile.Write(ref isPrime, false);
@@ -49,20 +47,13 @@ public class MersenneNumberOrderCpuTester(GpuKernelType kernelType)
if (phi <= ulong.MaxValue)
{
ulong phi64 = (ulong)phi;
// TODO: Switch these phi-based powmods to the shared windowed helper so CPU
// fallback paths keep pace with the optimized GPU kernels on large divisors.
if (phi64.PowModWithCycle(q, qCycle) == 1UL)
{
// TODO: Reuse the windowed pow2 helper for halfPow as soon as it is
// available instead of recalculating via square-and-multiply.
UInt128 halfPow = (phi64 >> 1).PowModWithCycle(q, qCycle) - 1UL;
if (halfPow.BinaryGcd(q) == 1UL)
{
ulong divMul = (ulong)((((UInt128)1 << 64) - 1UL) / exponent) + 1UL;
ulong div = phi64.FastDiv64(exponent, divMul);
// TODO: Replace this divisor powmod with the ProcessEightBitWindows
// implementation so order scans stop paying the slower bit-serial
// loop measured in the MulMod benchmarks.
UInt128 divPow = div.PowModWithCycle(q, qCycle) - 1UL;
if (divPow.BinaryGcd(q) == 1UL)
{