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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/MersenneNumberOrderCpuTester.cs
-9
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@@ -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)
{