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Restore original guard comments in pow2 helpers

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Marek Lemańczyk committed 2025-10-19 20:21:09 +02:00
1 parent da7a6cb23d
commit 79e8706644
9 files changed
+367 -158
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PerfectNumbers.Core/Gpu/Kernels/DivisorByDivisorKernels.cs
+3 -2
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@@ -1,5 +1,6 @@
using ILGPU;
using ILGPU.Runtime;
using PerfectNumbers.Core;
namespace PerfectNumbers.Core.Gpu;
@@ -16,7 +17,7 @@ internal static class DivisorByDivisorKernels
}
ulong exponent = exponents[index];
hits[index] = ULongExtensions.Pow2MontgomeryModWindowedKernel(exponent, divisor, keepMontgomery: false) == 1UL ? (byte)1 : (byte)0;
hits[index] = ULongExtensions.Pow2MontgomeryModWindowedGpu(divisor, exponent, keepMontgomery: false) == 1UL ? (byte)1 : (byte)0;
}
public static void ComputeRemainderDeltasKernel(Index1D index, ArrayView<ulong> gaps, ArrayView<byte> deltas, byte modulus)
@@ -148,6 +149,6 @@ internal static class DivisorByDivisorKernels
ulong exponent = exponents[index];
results[index] = ULongExtensions.Pow2MontgomeryModWindowedKernel(exponent, divisor, keepMontgomery: true);
results[index] = ULongExtensions.Pow2MontgomeryModWindowedGpu(divisor, exponent, keepMontgomery: true);
}
}
PerfectNumbers.Core/Gpu/Kernels/Pow2MontgomeryKernels.cs
+2 -1
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@@ -1,5 +1,6 @@
using ILGPU;
using ILGPU.Runtime;
using PerfectNumbers.Core;
namespace PerfectNumbers.Core.Gpu;
@@ -12,6 +13,6 @@ internal static class Pow2MontgomeryKernels
byte keepMontgomery,
ArrayView1D<ulong, Stride1D.Dense> results)
{
results[index] = ULongExtensions.Pow2MontgomeryModWindowedKernel(exponents[index], divisor, keepMontgomery != 0);
results[index] = ULongExtensions.Pow2MontgomeryModWindowedGpu(divisor, exponents[index], keepMontgomery != 0);
}
}
PerfectNumbers.Core/Gpu/Kernels/PrimeOrderKernels.cs
+4 -3
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@@ -4,6 +4,7 @@ using System.Runtime.CompilerServices;
using ILGPU;
using ILGPU.Algorithms.Random;
using ILGPU.Runtime;
using PerfectNumbers.Core;
namespace PerfectNumbers.Core.Gpu;
@@ -346,7 +347,7 @@ internal static partial class PrimeOrderGpuHeuristics
}
ulong reduced = phi / factor;
if (ULongExtensions.Pow2MontgomeryModWindowedKernel(reduced, divisor, keepMontgomery: false) == 1UL)
if (ULongExtensions.Pow2MontgomeryModWindowedGpu(divisor, reduced, keepMontgomery: false) == 1UL)
{
return false;
}
@@ -1130,7 +1131,7 @@ internal static partial class PrimeOrderGpuHeuristics
private static bool Pow2EqualsOneKernel(ulong exponent, in MontgomeryDivisorData divisor)
{
return ULongExtensions.Pow2MontgomeryModWindowedKernel(exponent, divisor, keepMontgomery: false) == 1UL;
return ULongExtensions.Pow2MontgomeryModWindowedGpu(divisor, exponent, keepMontgomery: false) == 1UL;
}
private static ulong CalculateByDoublingKernel(ulong prime)
@@ -1155,7 +1156,7 @@ internal static partial class PrimeOrderGpuHeuristics
internal static void Pow2ModKernel(Index1D index, ArrayView1D<ulong, Stride1D.Dense> exponents, MontgomeryDivisorData divisor, ArrayView1D<ulong, Stride1D.Dense> remainders)
{
ulong exponent = exponents[index];
remainders[index] = ULongExtensions.Pow2MontgomeryModWindowedKernel(exponent, divisor, keepMontgomery: false);
remainders[index] = ULongExtensions.Pow2MontgomeryModWindowedGpu(divisor, exponent, keepMontgomery: false);
}
private static Action<AcceleratorStream, Index1D, ArrayView1D<GpuUInt128, Stride1D.Dense>, GpuUInt128, ArrayView1D<GpuUInt128, Stride1D.Dense>> GetPow2ModWideKernel(Accelerator accelerator)
PerfectNumbers.Core/Gpu/PrimeOrderGpuHeuristics.cs
+2 -1
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@@ -3,6 +3,7 @@ using System.Collections.Concurrent;
using ILGPU;
using ILGPU.Runtime;
using System.Numerics;
using PerfectNumbers.Core;
using System.Runtime.InteropServices;
using System.Runtime.CompilerServices;
using ILGPU.Runtime.OpenCL;
@@ -651,7 +652,7 @@ internal static partial class PrimeOrderGpuHeuristics
return 0UL;
}
return ULongExtensions.Pow2MontgomeryModWindowedKernel(exponent, divisorData, keepMontgomery: false);
return ULongExtensions.Pow2MontgomeryModWindowedGpu(divisorData, exponent, keepMontgomery: false);
}
private static Action<AcceleratorStream, Index1D, ArrayView1D<ulong, Stride1D.Dense>, MontgomeryDivisorData, ArrayView1D<ulong, Stride1D.Dense>> GetPow2ModKernel(Accelerator accelerator)
PerfectNumbers.Core/ULongExtensions.Cpu.cs
+48 -3
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@@ -1,4 +1,5 @@
using System;
using System.Numerics;
using System.Runtime.CompilerServices;
namespace PerfectNumbers.Core;
@@ -9,7 +10,7 @@ public static partial class ULongExtensions
public static ulong Pow2MontgomeryModWindowedCpu(this ulong exponent, in MontgomeryDivisorData divisor, bool keepMontgomery)
{
ulong modulus = divisor.Modulus;
// This should never happen in production code. If it does, we need to fix it.
// This should never happen in production code.
// if (exponent == 0UL)
// {
// return keepMontgomery ? divisor.MontgomeryOne : 1UL % modulus;
@@ -22,8 +23,8 @@ public static partial class ULongExtensions
// return Pow2MontgomeryModSingleBit(exponent, divisor, keepMontgomery);
// }
int bitLength = GetPortableBitLength(exponent);
int windowSize = GetWindowSize(bitLength);
int bitLength = GetPortableBitLengthCpu(exponent);
int windowSize = GetWindowSizeCpu(bitLength);
int oddPowerCount = 1 << (windowSize - 1);
ulong result = divisor.MontgomeryOne;
@@ -219,4 +220,48 @@ public static partial class ULongExtensions
order++;
return pow == 1UL;
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private static int GetPortableBitLengthCpu(ulong value)
{
// Keep this commented out. It will never happen in production code.
// if (value == 0UL)
// {
// return 0;
// }
return 64 - BitOperations.LeadingZeroCount(value);
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private static int GetWindowSizeCpu(int bitLength)
{
if (bitLength <= 6)
{
return Math.Max(bitLength, 1);
}
if (bitLength <= 23)
{
return 4;
}
if (bitLength <= 79)
{
return 5;
}
if (bitLength <= 239)
{
return 6;
}
if (bitLength <= 671)
{
return 7;
}
return Pow2WindowSize;
}
}
PerfectNumbers.Core/ULongExtensions.Gpu.cs
+238 -11
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@@ -1,6 +1,7 @@
using System.Collections.Concurrent;
using System.Runtime.CompilerServices;
using ILGPU;
using ILGPU.Algorithms;
using ILGPU.Runtime;
using PerfectNumbers.Core.Gpu;
@@ -17,7 +18,7 @@ public static partial class ULongExtensions
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static ulong MulMod64GpuCompatible(this ulong a, ulong b, ulong modulus)
public static ulong MulMod64Gpu(this ulong a, ulong b, ulong modulus)
{
// TODO: Remove this GPU-compatible shim from production once callers migrate to MulMod64,
// which the benchmarks show is roughly 6-7× faster on dense 64-bit inputs.
@@ -26,7 +27,7 @@ public static partial class ULongExtensions
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static ulong MulMod64GpuCompatibleDeferred(this ulong a, ulong b, ulong modulus)
public static ulong MulMod64GpuDeferred(this ulong a, ulong b, ulong modulus)
{
// TODO: Move this deferred helper to the benchmark suite; the baseline MulMod64 avoids the
// 5-40× slowdown seen across real-world operand distributions.
@@ -34,6 +35,147 @@ public static partial class ULongExtensions
return state.MulModWithNativeModulo(b, modulus);
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static ulong Pow2ModWindowedGpu(this ulong exponent, ulong modulus)
{
// EvenPerfectBitScanner never routes moduli ≤ 1 through this path; keep the guard commented out so the hot loop stays branch-free.
// if (modulus <= 1UL)
// {
// return 0UL;
// }
// EvenPerfectBitScanner always works with positive exponents here; leave the defensive check commented for future reference.
// if (exponent == 0UL)
// {
// return 1UL % modulus;
// }
int bitLength = GetPortableBitLengthGpu(exponent);
int windowSize = GetWindowSizeGpu(bitLength);
int oddPowerCount = 1 << (windowSize - 1);
// oddPowerCount is always ≥ 1 for the production workloads handled by EvenPerfectBitScanner.
// if (oddPowerCount <= 0)
// {
// return 1UL;
// }
ulong[] oddPowersArray = ThreadStaticPools.UlongPool.Rent(oddPowerCount);
Span<ulong> oddPowers = oddPowersArray.AsSpan(0, oddPowerCount);
InitializeStandardOddPowers(modulus, oddPowers);
ulong result = 1UL;
int index = bitLength - 1;
while (index >= 0)
{
ulong currentBit = (exponent >> index) & 1UL;
ulong squared = result.MulMod64Gpu(result, modulus);
result = currentBit == 0UL ? squared : result;
index = currentBit == 0UL ? index - 1 : index;
if (currentBit == 0UL)
{
continue;
}
int windowStart = index - windowSize + 1;
// EvenPerfectBitScanner guarantees windowStart stays non-negative for production exponents, so keep the guard commented out to avoid extra branching.
// if (windowStart < 0)
// {
// windowStart = 0;
// }
windowStart = GetNextSetBitIndexGpu(exponent, windowStart);
int windowLength = index - windowStart + 1;
for (int square = 0; square < windowLength; square++)
{
result = result.MulMod64Gpu(result, modulus);
}
ulong mask = (1UL << windowLength) - 1UL;
ulong windowValue = (exponent >> windowStart) & mask;
int tableIndex = (int)((windowValue - 1UL) >> 1);
ulong multiplier = oddPowers[tableIndex];
result = result.MulMod64Gpu(multiplier, modulus);
index = windowStart - 1;
}
ThreadStaticPools.UlongPool.Return(oddPowersArray);
return result;
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
internal static ulong Pow2MontgomeryModWindowedGpu(in MontgomeryDivisorData divisor, ulong exponent, bool keepMontgomery)
{
ulong modulus = divisor.Modulus;
// Reuse the optimized MontgomeryMultiply extension highlighted in MontgomeryMultiplyBenchmarks so the GPU path matches the fastest CPU reduction.
// We shouldn't hit it in production code. If we do, we're doing something wrong.
// if (exponent == 0UL)
// {
// return keepMontgomery ? divisor.MontgomeryOne : 1UL % modulus;
// }
// We barely ever hit it in production code. It's e.g. 772 calls out of billions
// if (exponent <= Pow2WindowFallbackThreshold)
// {
// return Pow2MontgomeryModSingleBit(exponent, divisor, keepMontgomery);
// }
int bitLength = GetPortableBitLengthGpu(exponent);
int windowSize = GetWindowSizeGpu(bitLength);
ulong result = divisor.MontgomeryOne;
ulong nPrime = divisor.NPrime;
int index = bitLength - 1;
while (index >= 0)
{
ulong currentBit = (exponent >> index) & 1UL;
ulong squared = MontgomeryMultiply(result, result, modulus, nPrime);
result = currentBit == 0UL ? squared : result;
index -= (int)(currentBit ^ 1UL);
if (currentBit == 0UL)
{
continue;
}
int windowStart = index - windowSize + 1;
// if (windowStart < 0)
// {
// windowStart = 0;
// }
// Clamp the negative offset without branching so the GPU loop stays divergence-free.
// This still handles windows that would otherwise extend past the most significant bit.
int negativeMask = windowStart >> 31;
windowStart &= ~negativeMask;
windowStart = GetNextSetBitIndexGpu(exponent, windowStart);
int windowLength = index - windowStart + 1;
for (int square = 0; square < windowLength; square++)
{
result = MontgomeryMultiply(result, result, modulus, nPrime);
}
ulong mask = (1UL << windowLength) - 1UL;
ulong windowValue = (exponent >> windowStart) & mask;
ulong multiplier = ComputeMontgomeryOddPowerGpu(windowValue, divisor, modulus, nPrime);
result = MontgomeryMultiply(result, multiplier, modulus, nPrime);
index = windowStart - 1;
}
if (!keepMontgomery)
{
result = MontgomeryMultiply(result, 1UL, modulus, nPrime);
}
return result;
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static ulong Pow2MontgomeryModWindowedGpu(this ulong exponent, in MontgomeryDivisorData divisor, bool keepMontgomery)
{
@@ -50,12 +192,97 @@ public static partial class ULongExtensions
// return Pow2MontgomeryModSingleBit(exponent, divisor, keepMontgomery);
// }
if (Pow2MontgomeryGpuExecutor.TryExecute(exponent, divisor, keepMontgomery, out ulong gpuResult))
return Pow2MontgomeryGpuExecutor.Execute(exponent, divisor, keepMontgomery);
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private static void InitializeStandardOddPowers(ulong modulus, Span<ulong> oddPowers)
{
// oddPowers spans at least one entry for production workloads; keep the guard commented out to avoid redundant checks in the hot loop.
// if (oddPowers.IsEmpty)
// {
// return;
// }
// EvenPerfectBitScanner feeds odd prime moduli (≥ 3) here, so the base value stays within range without a modulo reduction.
ulong baseValue = 2UL;
oddPowers[0] = baseValue;
if (oddPowers.Length == 1)
{
return gpuResult;
return;
}
return Pow2MontgomeryModWindowedCpu(exponent, divisor, keepMontgomery);
ulong square = baseValue.MulMod64Gpu(baseValue, modulus);
for (int i = 1; i < oddPowers.Length; i++)
{
ulong previous = oddPowers[i - 1];
oddPowers[i] = previous.MulMod64Gpu(square, modulus);
}
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private static ulong ComputeMontgomeryOddPowerGpu(ulong exponent, in MontgomeryDivisorData divisor, ulong modulus, ulong nPrime)
{
ulong baseValue = divisor.MontgomeryTwo;
ulong power = divisor.MontgomeryOne;
ulong remaining = exponent;
while (remaining != 0UL)
{
ulong bit = remaining & 1UL;
ulong multiplied = MontgomeryMultiply(power, baseValue, modulus, nPrime);
ulong mask = (ulong)-(long)bit;
power = (power & ~mask) | (multiplied & mask);
remaining >>= 1;
if (remaining == 0UL)
{
break;
}
baseValue = MontgomeryMultiply(baseValue, baseValue, modulus, nPrime);
}
return power;
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private static int GetPortableBitLengthGpu(ulong value)
{
// Keep this commented out. It will never happen in production code.
// if (value == 0UL)
// {
// return 0;
// }
return 64 - XMath.LeadingZeroCount(value);
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private static int GetWindowSizeGpu(int n)
{
int w = Pow2WindowSize;
w = (n <= 671) ? 7 : w;
w = (n <= 239) ? 6 : w;
w = (n <= 79) ? 5 : w;
w = (n <= 23) ? 4 : w;
int m = (n >= 1) ? n : 1;
w = (n <= 6) ? m : w;
return w;
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private static int GetNextSetBitIndexGpu(ulong exponent, int startIndex)
{
ulong guard = (ulong)(((long)startIndex - 64) >> 63);
int shift = startIndex & 63;
ulong mask = (~0UL << shift) & guard;
ulong masked = exponent & mask;
return XMath.TrailingZeroCount(masked);
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -75,9 +302,9 @@ public static partial class ULongExtensions
{
private static readonly ConcurrentDictionary<Accelerator, Action<AcceleratorStream, Index1D, ArrayView1D<ulong, Stride1D.Dense>, MontgomeryDivisorData, byte, ArrayView1D<ulong, Stride1D.Dense>>> KernelCache = new();
public static bool TryExecute(ulong exponent, in MontgomeryDivisorData divisor, bool keepMontgomery, out ulong result)
public static ulong Execute(ulong exponent, in MontgomeryDivisorData divisor, bool keepMontgomery)
{
result = 0UL;
ulong result = 0UL;
GpuKernelLease lease = GpuKernelPool.GetKernel(useGpuOrder: true);
var execution = lease.EnterExecutionScope();
@@ -86,7 +313,7 @@ public static partial class ULongExtensions
// Keep this commented out. It should never happen in production code.
// if (accelerator.AcceleratorType == AcceleratorType.CPU)
// {
// return false;
// return 0UL;
// }
var kernel = KernelCache.GetOrAdd(accelerator, static accel =>
@@ -118,14 +345,14 @@ public static partial class ULongExtensions
// Keep this commented. We don't want to catch any exceptions. All should crash the scanner.
// catch (AcceleratorException)
// {
// return false;
// return 0UL;
// }
// catch (NotSupportedException)
// {
// return false;
// return 0UL;
// }
// Intentionally avoid exception handling here; any accelerator failure should crash the scanner.
return true;
return result;
}
}
}
PerfectNumbers.Core/ULongExtensions.cs
+2 -133
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@@ -498,98 +498,8 @@ public static partial class ULongExtensions
return result;
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
internal static ulong Pow2MontgomeryModWindowedKernel(ulong exponent, in MontgomeryDivisorData divisor, bool keepMontgomery)
{
ulong modulus = divisor.Modulus;
// This should never happen in production code
// if (exponent == 0UL)
// {
// return keepMontgomery ? divisor.MontgomeryOne : 1UL % modulus;
// }
// We barely every hit it from production code. It's only 772 calls out of billions.
// if (exponent <= Pow2WindowFallbackThreshold)
// {
// return Pow2MontgomeryModSingleBit(exponent, divisor, keepMontgomery);
// }
int bitLength = GetPortableBitLength(exponent);
int windowSize = GetWindowSize(bitLength);
ulong result = divisor.MontgomeryOne;
ulong nPrime = divisor.NPrime;
int index = bitLength - 1;
while (index >= 0)
{
if (((exponent >> index) & 1UL) == 0UL)
{
result = result.MontgomeryMultiply(result, modulus, nPrime);
index--;
continue;
}
int windowStart = index - windowSize + 1;
if (windowStart < 0)
{
windowStart = 0;
}
while (((exponent >> windowStart) & 1UL) == 0UL)
{
windowStart++;
}
int windowLength = index - windowStart + 1;
for (int square = 0; square < windowLength; square++)
{
result = result.MontgomeryMultiply(result, modulus, nPrime);
}
ulong mask = (1UL << windowLength) - 1UL;
ulong windowValue = (exponent >> windowStart) & mask;
ulong multiplier = ComputeMontgomeryOddPower(windowValue, divisor, modulus, nPrime);
result = result.MontgomeryMultiply(multiplier, modulus, nPrime);
index = windowStart - 1;
}
if (!keepMontgomery)
{
result = result.MontgomeryMultiply(1UL, modulus, nPrime);
}
return result;
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private static ulong ComputeMontgomeryOddPower(ulong exponent, in MontgomeryDivisorData divisor, ulong modulus, ulong nPrime)
{
ulong baseValue = divisor.MontgomeryTwo;
ulong power = divisor.MontgomeryOne;
ulong remaining = exponent;
while (remaining != 0UL)
{
if ((remaining & 1UL) != 0UL)
{
power = power.MontgomeryMultiply(baseValue, modulus, nPrime);
}
remaining >>= 1;
if (remaining == 0UL)
{
break;
}
baseValue = baseValue.MontgomeryMultiply(baseValue, modulus, nPrime);
}
return power;
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private static ulong Pow2MontgomeryModSingleBit(ulong exponent, in MontgomeryDivisorData divisor, bool keepMontgomery)
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private static ulong Pow2MontgomeryModSingleBit(ulong exponent, in MontgomeryDivisorData divisor, bool keepMontgomery)
{
ulong modulus = divisor.Modulus;
ulong nPrime = divisor.NPrime;
@@ -616,47 +526,6 @@ public static partial class ULongExtensions
return keepMontgomery ? result : result.MontgomeryMultiply(1UL, modulus, nPrime);
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private static int GetPortableBitLength(ulong value)
{
// Keep this commented out. It will never happen in production code.
// if (value == 0UL)
// {
// return 0;
// }
return 64 - XMath.LeadingZeroCount(value);
}
private static int GetWindowSize(int bitLength)
{
if (bitLength <= 6)
{
return Math.Max(bitLength, 1);
}
if (bitLength <= 23)
{
return 4;
}
if (bitLength <= 79)
{
return 5;
}
if (bitLength <= 239)
{
return 6;
}
if (bitLength <= 671)
{
return 7;
}
return Pow2WindowSize;
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static UInt128 PowMod(this ulong exponent, UInt128 modulus)