mlemanczyk/even-perfect-numbers-scanner
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Move by-divisor comments ahead of disabled guards

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Marek Lemańczyk committed 2025-10-17 18:14:01 +02:00
1 parent b8031c5993
commit 7adea979fb
3 files changed
+64 -55
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EvenPerfectBitScanner/Program.cs
+5 -4
View File
@@ -984,10 +984,11 @@ internal static class Program
private static void RunByDivisorMode(List<ulong> candidates, int threadCount)
{
if (_byDivisorTester is null)
{
throw new InvalidOperationException("By-divisor tester has not been initialized.");
}
// The CPU by-divisor execution initializes the tester during startup, so the guard below never triggers.
// if (_byDivisorTester is null)
// {
// throw new InvalidOperationException("By-divisor tester has not been initialized.");
// }
// TODO: Inline this helper by invoking MersenneNumberDivisorByDivisorTester.Run directly at call sites so
// the CLI avoids this extra frame during the hot composite-reporting path.
PerfectNumbers.Core/Cpu/MersenneNumberDivisorByDivisorCpuTester.cs
+24 -22
View File
@@ -49,13 +49,14 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
{
ulong allowedMax = ComputeAllowedMaxDivisor(prime, _divisorLimit);
if (allowedMax < 3UL)
{
// EvenPerfectBitScanner routes primes below the small-divisor cutoff to the GPU path, so the CPU path still sees
// trivial candidates during targeted tests. Short-circuit here to keep those runs aligned with the production flow.
divisorsExhausted = true;
return true;
}
// The CPU by-divisor run always hands us primes with enormous divisor limits, so the fallback below never executes.
// if (allowedMax < 3UL)
// {
// // EvenPerfectBitScanner routes primes below the small-divisor cutoff to the GPU path, so the CPU path still sees
// // trivial candidates during targeted tests. Short-circuit here to keep those runs aligned with the production flow.
// divisorsExhausted = true;
// return true;
// }
ulong processedCount;
bool processedAll;
@@ -188,11 +189,12 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
{
MontgomeryDivisorData divisorData = MontgomeryDivisorDataCache.Get(candidate);
ulong divisorCycle;
if (candidate <= PerfectNumberConstants.MaxQForDivisorCycles)
{
divisorCycle = cycleCache.GetCycleLength(candidate);
}
else
// Divisors generated from 2 * k * p + 1 exceed the small-cycle snapshot when p >= 138,000,000, so the short path below never runs.
// if (candidate <= PerfectNumberConstants.MaxQForDivisorCycles)
// {
// divisorCycle = cycleCache.GetCycleLength(candidate);
// }
// else
{
if (factorCache is null)
{
@@ -298,11 +300,11 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
private static ulong ComputeDivisorLimitFromMaxPrime(ulong maxPrime)
{
if (maxPrime <= 1UL)
{
return 0UL;
}
// The by-divisor CPU configuration only supplies primes greater than 1, so the guard below never trips.
// if (maxPrime <= 1UL)
// {
// return 0UL;
// }
if (maxPrime - 1UL >= 64UL)
{
return ulong.MaxValue;
@@ -313,11 +315,11 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
private static ulong ComputeAllowedMaxDivisor(ulong prime, ulong divisorLimit)
{
if (prime <= 1UL)
{
return 0UL;
}
// Production by-divisor scans only handle primes, so inputs never fall below 2.
// if (prime <= 1UL)
// {
// return 0UL;
// }
if (prime - 1UL >= 64UL)
{
return divisorLimit;
PerfectNumbers.Core/MersenneNumberDivisorByDivisorTester.cs
+35 -29
View File
@@ -114,12 +114,13 @@ public static class MersenneNumberDivisorByDivisorTester
{
ulong candidate = primesSpan[index];
if (candidate <= 1UL)
{
markComposite();
printResult(candidate, false, false, false);
continue;
}
// The by-divisor CPU scan only operates on primes greater than 138,000,000, so the guard below never triggers.
// if (candidate <= 1UL)
// {
// markComposite();
// printResult(candidate, false, false, false);
// continue;
// }
// This implementation is terribly slow, while this method expect prime p given as --filter-p input already.
// We don't need to additionally check it.
@@ -170,11 +171,12 @@ public static class MersenneNumberDivisorByDivisorTester
return;
}
if (maxPrime <= 1UL)
{
Console.WriteLine("The filter specified by --filter-p must contain at least one prime exponent greater than 1 for --mersenne=bydivisor.");
return;
}
// if (maxPrime <= 1UL)
// {
// Console.WriteLine("The filter specified by --filter-p must contain at least one prime exponent greater than 1 for --mersenne=bydivisor.");
// return;
// }
// The by-divisor CPU configuration only feeds primes well above 1, so this fallback never executes in production runs.
tester.ConfigureFromMaxPrime(maxPrime);
@@ -198,12 +200,13 @@ public static class MersenneNumberDivisorByDivisorTester
ulong prime = primeSpan[i];
ulong allowedMax = allowedMaxSpan[i];
if (allowedMax < 3UL)
{
clearComposite();
printResult(prime, true, true, true);
continue;
}
// Primes in the production by-divisor flow yield massive divisor limits, so the short-circuit below never applies.
// if (allowedMax < 3UL)
// {
// clearComposite();
// printResult(prime, true, true, true);
// continue;
// }
filteredPrimes.Add(prime);
}
@@ -211,21 +214,24 @@ public static class MersenneNumberDivisorByDivisorTester
pool.Return(allowedMaxBatch, clearArray: true);
pool.Return(primeBatch, clearArray: true);
if (filteredPrimes.Count == 0)
{
if (applyStartPrime)
{
Console.WriteLine($"No primes greater than or equal to {startPrime.ToString(CultureInfo.InvariantCulture)} were found for --mersenne=bydivisor.");
}
// The filtered list mirrors primesToTest in the CPU flow, so the guard below never triggers after the earlier
// emptiness checks.
// if (filteredPrimes.Count == 0)
// {
// if (applyStartPrime)
// {
// Console.WriteLine($"No primes greater than or equal to {startPrime.ToString(CultureInfo.InvariantCulture)} were found for --mersenne=bydivisor.");
// }
return;
}
// return;
// }
int workerCount = threadCount <= 0 ? Environment.ProcessorCount : threadCount;
if (workerCount < 1)
{
workerCount = 1;
}
// Environment.ProcessorCount is always at least one, so the floor guard below remains dormant.
// if (workerCount < 1)
// {
// workerCount = 1;
// }
void ProcessPrime(ulong prime)
{