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Switch GPU powmod host helpers to simplified mul-mod

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Marek Lemańczyk committed 2025-10-25 02:20:09 +02:00
1 parent 03194650c9
commit 4b13bc6497
2 files changed
+7 -7
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PerfectNumbers.Core/ULongExtensions.Gpu.cs
+5 -5
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@@ -81,7 +81,7 @@ public static partial class ULongExtensions
while (index >= 0) while (index >= 0)
{ {
ulong currentBit = (exponent >> index) & 1UL; ulong currentBit = (exponent >> index) & 1UL;
ulong squared = result.MulMod64(result, modulus); ulong squared = result.GpuCompatibleMulModSimplifiedExtension(result, modulus);
result = currentBit == 0UL ? squared : result; result = currentBit == 0UL ? squared : result;
index = currentBit == 0UL ? index - 1 : index; index = currentBit == 0UL ? index - 1 : index;
if (currentBit == 0UL) if (currentBit == 0UL)
@@ -101,14 +101,14 @@ public static partial class ULongExtensions
int windowLength = index - windowStart + 1; int windowLength = index - windowStart + 1;
for (int square = 0; square < windowLength; square++) for (int square = 0; square < windowLength; square++)
{ {
result = result.MulMod64(result, modulus); result = result.GpuCompatibleMulModSimplifiedExtension(result, modulus);
} }
ulong mask = (1UL << windowLength) - 1UL; ulong mask = (1UL << windowLength) - 1UL;
ulong windowValue = (exponent >> windowStart) & mask; ulong windowValue = (exponent >> windowStart) & mask;
int tableIndex = (int)((windowValue - 1UL) >> 1); int tableIndex = (int)((windowValue - 1UL) >> 1);
ulong multiplier = oddPowers[tableIndex]; ulong multiplier = oddPowers[tableIndex];
result = result.MulMod64(multiplier, modulus); result = result.GpuCompatibleMulModSimplifiedExtension(multiplier, modulus);
index = windowStart - 1; index = windowStart - 1;
} }
@@ -311,11 +311,11 @@ public static partial class ULongExtensions
return; return;
} }
ulong square = baseValue.MulMod64(baseValue, modulus); ulong square = baseValue.GpuCompatibleMulModSimplifiedExtension(baseValue, modulus);
for (int i = 1; i < oddPowers.Length; i++) for (int i = 1; i < oddPowers.Length; i++)
{ {
ulong previous = oddPowers[i - 1]; ulong previous = oddPowers[i - 1];
oddPowers[i] = previous.MulMod64(square, modulus); oddPowers[i] = previous.GpuCompatibleMulModSimplifiedExtension(square, modulus);
} }
} }
docs/gpu-bydivisor-mulmod-audit.md
+2 -2
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@@ -8,8 +8,8 @@ This note tracks every `MulMod` call site in the GPU-only `--mersenne=bydivisor`
| --- | --- | | --- | --- |
| `ULongExtensions.GpuCompatibleMulModSimplifiedExtension` | Wraps `GpuUInt128.MulModSimplified` so host code mirrors the benchmark winner without reimplementing GPU logic.【F:PerfectNumbers.Core/ULongExtensions.Gpu.cs†L23-L31】 | | `ULongExtensions.GpuCompatibleMulModSimplifiedExtension` | Wraps `GpuUInt128.MulModSimplified` so host code mirrors the benchmark winner without reimplementing GPU logic.【F:PerfectNumbers.Core/ULongExtensions.Gpu.cs†L23-L31】 |
| `ULongExtensions.MulMod64Gpu` | Marked obsolete; migrate to `ULongExtensions.GpuCompatibleMulModSimplifiedExtension` for GPU-compatible host code or `GpuUInt128.MulMod` when running inside kernels.【F:PerfectNumbers.Core/ULongExtensions.Gpu.cs†L17-L24】 | | `ULongExtensions.MulMod64Gpu` | Marked obsolete; migrate to `ULongExtensions.GpuCompatibleMulModSimplifiedExtension` for GPU-compatible host code or `GpuUInt128.MulMod` when running inside kernels.【F:PerfectNumbers.Core/ULongExtensions.Gpu.cs†L17-L24】 |
| `ULongExtensions.Pow2ModWindowedGpu` | Migrated to call `MulMod64` for every square and multiply, eliminating the 6–18× slowdown that the shim introduced while executing on the host.【F:PerfectNumbers.Core/ULongExtensions.Gpu.cs†L39-L109】 | | `ULongExtensions.Pow2ModWindowedGpu` | Migrated to call `GpuCompatibleMulModSimplifiedExtension` for every square and multiply, eliminating the 6–18× slowdown that the shim introduced while executing on the host and aligning host math with the new production helper.【F:PerfectNumbers.Core/ULongExtensions.Gpu.cs†L39-L109】 |
| `ULongExtensions.InitializeStandardOddPowers` | Populates the odd-power table through `MulMod64`, so the host setup costs now match the CPU benchmark baseline.【F:PerfectNumbers.Core/ULongExtensions.Gpu.cs†L286-L309】 | | `ULongExtensions.InitializeStandardOddPowers` | Populates the odd-power table through `GpuCompatibleMulModSimplifiedExtension`, so the host setup costs now match the GPU-compatible benchmark winner.【F:PerfectNumbers.Core/ULongExtensions.Gpu.cs†L286-L309】 |
All host-executed `MulMod` operations in the GPU pipeline now target the optimized CPU helper. All host-executed `MulMod` operations in the GPU pipeline now target the optimized CPU helper.