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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/Gpu/MersenneNumberDivisorGpuTester.cs
+18 -10
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@@ -75,6 +75,8 @@ public sealed class MersenneNumberDivisorGpuTester
for (int k = 0; k < len; k++)
{
(ulong dSmall, cycle) = candidates[k];
// TODO: Replace this `%` check with the shared divisor-cycle divisibility helper so GPU scans
// reuse the cached cycle remainders instead of recomputing modulo for every candidate.
if (p % cycle != 0UL)
{
continue;
@@ -109,10 +111,12 @@ public sealed class MersenneNumberDivisorGpuTester
}
UInt128 cycle128 = MersenneDivisorCycles.GetCycle(d);
if ((UInt128)p % cycle128 != UInt128.Zero)
{
continue;
}
// TODO: Feed this check through the ProcessEightBitWindows-based residue tracker so we avoid the slow
// UInt128 modulo on the CPU fallback highlighted by the Pow2Montgomery benchmarks.
if ((UInt128)p % cycle128 != UInt128.Zero)
{
continue;
}
if (IsDivisible(p, d))
{
@@ -138,9 +142,11 @@ public sealed class MersenneNumberDivisorGpuTester
? 63 - XMath.LeadingZeroCount(divisor.Low)
: 127 - XMath.LeadingZeroCount(divisor.High);
mod = divisor;
if (x == 0)
{
baseVal = GpuUInt128.Pow2Mod(exponent, mod);
if (x == 0)
{
// TODO: Swap Pow2Mod for the ProcessEightBitWindows helper once Pow2Minus1Mod adopts it;
// GpuPow2ModBenchmarks showed the windowed kernel cutting large divisors from ~51 µs to ~21 µs.
baseVal = GpuUInt128.Pow2Mod(exponent, mod);
result[0] = baseVal.High == 0UL && baseVal.Low == 1UL ? (byte)1 : (byte)0;
return;
}
@@ -155,9 +161,11 @@ public sealed class MersenneNumberDivisorGpuTester
baseVal = new GpuUInt128(0UL, 1UL << x);
}
GpuUInt128 pow = baseVal;
pow.ModPow(exponent / ux, mod);
var part2 = GpuUInt128.Pow2Mod(exponent % ux, mod);
GpuUInt128 pow = baseVal;
pow.ModPow(exponent / ux, mod);
// TODO: Replace this trailing Pow2Mod call with the ProcessEightBitWindows variant once the shared
// windowed helper lands so mixed-radix decompositions benefit from the same GPU speedup.
var part2 = GpuUInt128.Pow2Mod(exponent % ux, mod);
GpuUInt128 product = pow;
product.MulMod(part2, mod);
result[0] = product.High == 0UL && product.Low == 1UL ? (byte)1 : (byte)0;