mlemanczyk/even-perfect-numbers-scanner
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Switch GPU pow2mod helpers to plain windowed arithmetic

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Marek Lemańczyk committed 2025-10-13 14:21:35 +02:00
1 parent 1916196e89
commit 79695b0c56
5 files changed
+305 -74
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PerfectNumbers.Core/Gpu/MersenneNumberDivisorByDivisorGpuTester.cs
+22 -16
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@@ -545,10 +545,12 @@ public sealed class MersenneNumberDivisorByDivisorGpuTester : IMersenneNumberDiv
private static ulong ComputeAllowedMaxDivisor(ulong prime, ulong divisorLimit)
{
if (prime <= 1UL)
{
return 0UL;
}
// The by-divisor search emits candidate exponents starting at the first odd prime, so this guard
// would never trigger on the scanner hot path.
// if (prime <= 1UL)
// {
// return 0UL;
// }
if (prime - 1UL >= 64UL)
{
@@ -562,14 +564,16 @@ public sealed class MersenneNumberDivisorByDivisorGpuTester : IMersenneNumberDiv
{
MontgomeryDivisorData divisor = divisors[index];
ulong modulus = divisor.Modulus;
if (modulus <= 1UL || (modulus & 1UL) == 0UL)
{
hits[index] = 0;
return;
}
// The divisor staging path filters out non-prime and even moduli before they reach the device, so this guard
// would never fire for EvenPerfectBitScanner workloads.
// if (modulus <= 1UL || (modulus & 1UL) == 0UL)
// {
// hits[index] = 0;
// return;
// }
ulong exponent = exponents[index];
hits[index] = exponent.Pow2ModBinaryGpu(modulus) == 1UL ? (byte)1 : (byte)0;
hits[index] = exponent.Pow2ModWindowedGpu(modulus) == 1UL ? (byte)1 : (byte)0;
}
public sealed class DivisorScanSession : IMersenneNumberDivisorByDivisorTester.IDivisorScanSession
@@ -780,15 +784,17 @@ public sealed class MersenneNumberDivisorByDivisorGpuTester : IMersenneNumberDiv
private static void ComputeExponentKernel(Index1D index, MontgomeryDivisorData divisor, ArrayView<ulong> exponents, ArrayView<ulong> results)
{
ulong modulus = divisor.Modulus;
if (modulus <= 1UL || (modulus & 1UL) == 0UL)
{
results[index] = 0UL;
return;
}
// Kernel inputs are constrained to odd prime moduli, so this defensive branch would never execute on the configured
// scanning path.
// if (modulus <= 1UL || (modulus & 1UL) == 0UL)
// {
// results[index] = 0UL;
// return;
// }
ulong exponent = exponents[index];
results[index] = exponent.Pow2ModBinaryGpu(modulus);
results[index] = exponent.Pow2ModWindowedGpu(modulus);
}
public ulong DivisorLimit