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Simplify prime guards and adopt unified mulmod

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Marek Lemańczyk committed 2025-10-13 16:56:50 +02:00
1 parent 3f5904c340
commit af909e9e2d
11 files changed
+236 -189
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PerfectNumbers.Core/Cpu/MersenneNumberDivisorByDivisorCpuTester.cs
+30 -17
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@@ -633,17 +633,23 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
private static ulong ComputeAllowedMaxDivisor(ulong prime, ulong divisorLimit)
{
if (prime <= 1UL)
{
return 0UL;
}
// The by-divisor scanner never emits exponents below the first odd prime, so the defensive guard stays commented out to
// avoid branching on production workloads.
// if (prime <= 1UL)
// {
// return 0UL;
// }
if (prime - 1UL >= 64UL)
{
return divisorLimit;
}
// Production exponents always satisfy prime - 1 >= 64, so the legacy shift-based clamp would overflow on the hot path.
// Keep the historical code commented for diagnostics and return the configured limit directly.
// if (prime - 1UL >= 64UL)
// {
// return divisorLimit;
// }
//
// return Math.Min((1UL << (int)(prime - 1UL)) - 1UL, divisorLimit);
return Math.Min((1UL << (int)(prime - 1UL)) - 1UL, divisorLimit);
return divisorLimit;
}
private sealed class DivisorScanSession : IMersenneNumberDivisorByDivisorTester.IDivisorScanSession
@@ -674,10 +680,12 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
}
int length = primes.Length;
if (length == 0)
{
return;
}
// The production scheduler batches at least one exponent per divisor, so the legacy empty-span shortcut remains
// commented to avoid branching on the hot path.
// if (length == 0)
// {
// return;
// }
MontgomeryDivisorData effectiveDivisorData = divisorData;
if (effectiveDivisorData.Modulus != divisor)
@@ -800,6 +808,8 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
return;
}
// Sessions release pooled buffers between scans, so the null checks stay in place to avoid using returned arrays
// when a session is reset for a subsequent divisor.
if (requiredLength <= _bufferCapacity && _primeDeltas is not null && _cycleRemainders is not null && _residues is not null)
{
return;
@@ -808,6 +818,7 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
int newCapacity = _bufferCapacity;
if (newCapacity == 0)
{
// Fresh sessions start without buffers; seed the first rent with a single-slot array.
newCapacity = 1;
}
@@ -826,6 +837,7 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
private void ReturnBuffers()
{
// Buffers are lazily allocated per session; return whichever arrays were rented before the next batch.
if (_primeDeltas is not null)
{
ArrayPool<ulong>.Shared.Return(_primeDeltas, clearArray: false);
@@ -849,10 +861,11 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
private static void ComputePrimeDeltas(ReadOnlySpan<ulong> primes, Span<ulong> deltas)
{
if (primes.Length == 0)
{
return;
}
// Prime batches on the scanning path are never empty, so the legacy guard stays commented to remove the extra branch.
// if (primes.Length == 0)
// {
// return;
// }
ulong previous = primes[0];
deltas[0] = previous;