mlemanczyk/even-perfect-numbers-scanner
1
0 Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

Make GPU mask compaction branchless with shared staging

Browse Source
This commit is contained in:
Marek Lemańczyk committed 2025-10-22 22:01:39 +02:00
1 parent ea0770a84a
commit 4d9158e8f3
2 files changed
+38 -19
Download Patch File Download Diff File Expand all files Collapse all files

No files matched your search

PerfectNumbers.Core/Gpu/Kernels/DivisorByDivisorKernels.cs
+36 -18
View File
@@ -1,4 +1,5 @@
using ILGPU;
using ILGPU.Algorithms;
using ILGPU.Runtime;
using PerfectNumbers.Core;
@@ -179,43 +180,60 @@ internal static class DivisorByDivisorKernels
int groupSize = Group.Dimension.X;
var shared = SharedMemory.GetDynamic<int>();
int prefixBase = 0;
int mappingBase = length;
int fallbackBase = length * 2;
// The dynamic shared-memory slice stores prefix sums, compacted index mappings, and fallback slots
// in separate regions so the scatter stage can avoid divergent branches.
byte maskValue = mask[globalIndex];
int accepted = maskValue != 0 ? 1 : 0;
shared[localIndex] = accepted;
ulong candidateValue = sourceCandidates[globalIndex];
shared[prefixBase + localIndex] = accepted;
shared[fallbackBase + localIndex] = globalIndex;
Group.Barrier();
int offset = 1;
while (offset < groupSize)
{
int addend = localIndex >= offset ? shared[localIndex - offset] : 0;
int addendIndex = prefixBase + localIndex - offset;
int addend = localIndex >= offset ? shared[addendIndex] : 0;
Group.Barrier();
int current = shared[localIndex];
int currentIndex = prefixBase + localIndex;
int current = shared[currentIndex];
int sum = current + addend;
if (localIndex >= offset)
{
shared[localIndex] = sum;
}
int shouldUpdate = localIndex >= offset ? 1 : 0;
shared[currentIndex] = shouldUpdate != 0 ? sum : current;
Group.Barrier();
offset <<= 1;
}
if (accepted != 0)
{
int targetIndex = shared[localIndex] - 1;
compactedCandidates[targetIndex] = candidateValue;
}
int inclusivePrefix = shared[prefixBase + localIndex];
int exclusiveIndex = inclusivePrefix - accepted;
int targetBase = accepted != 0 ? mappingBase : fallbackBase;
int targetOffset = accepted != 0 ? exclusiveIndex : localIndex;
shared[targetBase + targetOffset] = globalIndex;
if (globalIndex == length - 1)
{
compactedCount[0] = shared[localIndex];
}
Group.Barrier();
int totalAccepted = shared[prefixBase + length - 1];
int writerMask = localIndex < totalAccepted ? 1 : 0;
int lookupBase = writerMask != 0 ? mappingBase : fallbackBase;
int sourceIndex = shared[lookupBase + localIndex];
ulong candidateValue = sourceCandidates[sourceIndex];
int destinationIndex = localIndex;
ulong existingValue = compactedCandidates[destinationIndex];
compactedCandidates[destinationIndex] = writerMask != 0 ? candidateValue : existingValue;
int lastLaneMask = globalIndex == length - 1 ? 1 : 0;
int countValue = shared[prefixBase + localIndex];
int storedCount = lastLaneMask != 0 ? countValue : 0;
Atomic.Max(ref compactedCount[0], storedCount);
}
public static void ComputeMontgomeryExponentKernel(Index1D index, MontgomeryDivisorData divisor, ArrayView<ulong> exponents, ArrayView<ulong> results)