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Adopt fixed stack capacities for CPU prime order helpers

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Marek Lemańczyk committed 2025-10-21 19:46:59 +02:00
1 parent c15405e3b1
commit b418d79fb3
1 file changed
+34 -37
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PerfectNumbers.Core/PrimeOrderCalculator.Cpu.cs
+34 -37
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@@ -1,3 +1,4 @@
using System;
using System.Buffers;
using System.Diagnostics;
using System.Numerics;
@@ -213,18 +214,11 @@ internal static partial class PrimeOrderCalculator
ExponentRemainderStepper stepper = ThreadStaticPools.RentExponentStepper(divisorData);
int maxStackExponent = 0;
for (int i = 0; i < length; i++)
{
int exponent = buffer[i].Exponent;
if (exponent <= 16 && exponent > maxStackExponent)
{
maxStackExponent = exponent;
}
}
const int StackExponentCapacity = 16;
const int ExponentHardLimit = 256;
Span<ulong> stackCandidates = maxStackExponent > 0 ? stackalloc ulong[maxStackExponent] : Span<ulong>.Empty;
Span<bool> stackEvaluations = maxStackExponent > 0 ? stackalloc bool[maxStackExponent] : Span<bool>.Empty;
Span<ulong> stackCandidates = stackalloc ulong[StackExponentCapacity];
Span<bool> stackEvaluations = stackalloc bool[StackExponentCapacity];
for (int i = 0; i < length; i++)
{
@@ -233,10 +227,17 @@ internal static partial class PrimeOrderCalculator
// Factor exponents produced by Pollard-Rho and trial division are always positive in the scanner flow.
// if (exponent <= 0)
// {
// continue;
// continue;
// }
if (exponent <= 16)
if (exponent > ExponentHardLimit)
{
ThreadStaticPools.ReturnExponentStepper(stepper);
pool.Return(tempArray, clearArray: false);
throw new InvalidOperationException($"Prime factor exponent {exponent} exceeds the supported limit of {ExponentHardLimit}.");
}
if (exponent <= StackExponentCapacity)
{
ProcessExponentLoweringPrime(stackCandidates.Slice(0, exponent), stackEvaluations.Slice(0, exponent), ref order, primeFactor, exponent, ref stepper);
}
@@ -368,17 +369,10 @@ internal static partial class PrimeOrderCalculator
ReadOnlySpan<FactorEntry> span = factorization.Factors!;
int length = factorization.Count;
int maxStackExponent = 0;
for (int i = 0; i < length; i++)
{
int exponent = span[i].Exponent;
if (exponent <= 32 && exponent > maxStackExponent)
{
maxStackExponent = exponent;
}
}
const int StackExponentCapacity = 32;
const int ExponentHardLimit = 256;
Span<ulong> stackBuffer = maxStackExponent > 0 ? stackalloc ulong[maxStackExponent] : Span<ulong>.Empty;
Span<ulong> stackBuffer = stackalloc ulong[StackExponentCapacity];
for (int i = 0; i < length; i++)
{
@@ -387,10 +381,15 @@ internal static partial class PrimeOrderCalculator
// Factor exponents emitted by TryConfirmCandidateCpu stay positive for production workloads.
// if (exponent <= 0)
// {
// continue;
// continue;
// }
if (exponent <= 32)
if (exponent > ExponentHardLimit)
{
throw new InvalidOperationException($"Factor exponent {exponent} exceeds the supported limit of {ExponentHardLimit}.");
}
if (exponent <= StackExponentCapacity)
{
if (ValidateOrderForFactor(stackBuffer.Slice(0, exponent), primeFactor, exponent, order, divisorData))
{
@@ -830,17 +829,10 @@ internal static partial class PrimeOrderCalculator
ReadOnlySpan<FactorEntry> span = factorization.Factors;
int length = factorization.Count;
int maxStackExponent = 0;
for (int i = 0; i < length; i++)
{
int exponent = span[i].Exponent;
if (exponent <= 32 && exponent > maxStackExponent)
{
maxStackExponent = exponent;
}
}
const int StackExponentCapacity = 32;
const int ExponentHardLimit = 256;
Span<ulong> stackBuffer = maxStackExponent > 0 ? stackalloc ulong[maxStackExponent] : Span<ulong>.Empty;
Span<ulong> stackBuffer = stackalloc ulong[StackExponentCapacity];
for (int i = 0; i < length; i++)
{
@@ -849,10 +841,15 @@ internal static partial class PrimeOrderCalculator
// Factorization entries for candidate confirmation are always positive here.
// if (exponent <= 0)
// {
// continue;
// continue;
// }
if (exponent <= 32)
if (exponent > ExponentHardLimit)
{
throw new InvalidOperationException($"Candidate factor exponent {exponent} exceeds the supported limit of {ExponentHardLimit}.");
}
if (exponent <= StackExponentCapacity)
{
if (CheckCandidateViolation(stackBuffer.Slice(0, exponent), primeFactor, exponent, candidate, prime, divisorData, ref powUsed, powBudget))
{