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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
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@@ -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
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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)
{
PerfectNumbers.Core/ExponentRemainderStepper.cs
-11
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@@ -44,9 +44,6 @@ internal struct ExponentRemainderStepper
if (!_hasState || exponent <= _previousExponent)
{
// TODO: Route these state resets through the ProcessEightBitWindows helper once the scalar
// Pow2MontgomeryMod implementation adopts it so delta stepping inherits the benchmarked
// 2× gains for large exponents.
_currentMontgomery = exponent.Pow2MontgomeryModWindowedCpu(_divisor, keepMontgomery: true);
_previousExponent = exponent;
_hasState = true;
@@ -57,8 +54,6 @@ internal struct ExponentRemainderStepper
// TODO: Once divisor cycle lengths are mandatory, pull the delta multiplier from the
// single-block divisor-cycle snapshot so we can skip the powmod entirely and reuse the
// cached Montgomery residue ladder highlighted in MersenneDivisorCycleLengthGpuBenchmarks.
// TODO: Replace this per-delta powmod with the upcoming windowed ladder so incremental
// updates stop paying the single-bit cost highlighted in GpuPow2ModBenchmarks.
ulong multiplier = delta.Pow2MontgomeryModWindowedCpu(_divisor, keepMontgomery: true);
_currentMontgomery = _currentMontgomery.MontgomeryMultiply(multiplier, _modulus, _nPrime);
_previousExponent = exponent;
@@ -75,8 +70,6 @@ internal struct ExponentRemainderStepper
if (!_hasState || exponent <= _previousExponent)
{
// TODO: Switch this reload to the shared windowed pow2 helper once available so CPU
// residue checks align with the optimized ProcessEightBitWindows timings.
_currentMontgomery = exponent.Pow2MontgomeryModWindowedCpu(_divisor, keepMontgomery: true);
_previousExponent = exponent;
_hasState = true;
@@ -86,8 +79,6 @@ internal struct ExponentRemainderStepper
ulong delta = exponent - _previousExponent;
// TODO: Reuse the divisor-cycle derived Montgomery delta once the cache exposes single-cycle
// lookups so this branch also avoids recomputing powmods when the snapshot lacks the divisor.
// TODO: Use the windowed delta pow2 helper here as well to avoid the single-bit ladder that
// currently lags behind the benchmarked implementation for huge divisor cycles.
ulong multiplier = delta.Pow2MontgomeryModWindowedCpu(_divisor, keepMontgomery: true);
_currentMontgomery = _currentMontgomery.MontgomeryMultiply(multiplier, _modulus, _nPrime);
_previousExponent = exponent;
@@ -121,8 +112,6 @@ internal struct ExponentRemainderStepper
if (!_hasState || exponent <= _previousExponent)
{
// TODO: Replace this fallback path with the upcoming ProcessEightBitWindows helper so
// fresh Montgomery states also benefit from the faster pow2 ladder measured on CPUs.
_currentMontgomery = exponent.Pow2MontgomeryModWindowedCpu(_divisor, keepMontgomery: true);
_previousExponent = exponent;
_hasState = true;
PerfectNumbers.Core/MersenneNumberTester.cs
-4
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@@ -94,8 +94,6 @@ public sealed class MersenneNumberTester(
continue;
}
// TODO: Swap this fallback to the shared windowed order helper once CalculateOrder migrates
// to the ProcessEightBitWindows pipeline so warm-ups stop invoking the slower legacy powmod.
ulong ord = q.CalculateOrder();
OrderCache[q] = ord;
}
@@ -184,8 +182,6 @@ public sealed class MersenneNumberTester(
ulong order = orders[i];
if (order == 0UL)
{
// TODO: Replace this CalculateOrder call with the upcoming windowed helper so
// GPU warm-ups reuse the faster pow2 ladder measured in the CPU order benchmarks.
order = qs[offset + i].CalculateOrder();
}
PerfectNumbers.Core/UInt128Extensions.cs
-2
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@@ -553,8 +553,6 @@ public static class UInt128Extensions
while (order % prime == 0UL)
{
temp = order / prime;
// TODO: Switch this divisor-order powmod to the ProcessEightBitWindows helper so the
// cycle factoring loop benefits from the faster windowed pow2 ladder measured in CPU benchmarks.
if (temp.PowModWithCycle(q, cycle) == one)
{
order = temp;