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Merge pull request #173 from mlemanczyk/codex/analyze-and-reduce-gc-cost-in-primeordercalculator

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Reduce Pollard Rho stopwatch allocations to lower GC pressure
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Marek Lemańczyk authored and GitHub committed 2025-10-15 04:39:59 +02:00
2 parents 77bc2601f1 0b831b5a23
commit a70113a99d
2 files changed
+80 -47
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PerfectNumbers.Core/PrimeOrderCalculator.Wide.cs
+9 -6
View File
@@ -603,12 +603,12 @@ internal static partial class PrimeOrderCalculator
if (config.PollardRhoMilliseconds > 0 && pending.Count > 0)
{
Stopwatch stopwatch = Stopwatch.StartNew();
long budgetTicks = TimeSpan.FromMilliseconds(config.PollardRhoMilliseconds).Ticks;
long deadlineTimestamp = CreateDeadlineTimestamp(config.PollardRhoMilliseconds);
Stack<UInt128> stack = new();
stack.Push(remaining);
pending.Clear();
long timestamp = 0L; // reused for deadline checks.
while (stack.Count > 0)
{
UInt128 composite = stack.Pop();
@@ -623,13 +623,14 @@ internal static partial class PrimeOrderCalculator
continue;
}
if (stopwatch.ElapsedTicks > budgetTicks)
timestamp = Stopwatch.GetTimestamp();
if (timestamp > deadlineTimestamp)
{
pending.Add(composite);
continue;
}
if (!TryPollardRhoWide(composite, stopwatch, budgetTicks, out UInt128 factor))
if (!TryPollardRhoWide(composite, deadlineTimestamp, out UInt128 factor))
{
pending.Add(composite);
continue;
@@ -728,7 +729,7 @@ internal static partial class PrimeOrderCalculator
return remaining;
}
private static bool TryPollardRhoWide(in UInt128 n, Stopwatch stopwatch, long budgetTicks, out UInt128 factor)
private static bool TryPollardRhoWide(in UInt128 n, long deadlineTimestamp, out UInt128 factor)
{
factor = UInt128.Zero;
if ((n & UInt128.One) == UInt128.Zero)
@@ -740,10 +741,12 @@ internal static partial class PrimeOrderCalculator
UInt128 c = UInt128.One;
UInt128 x = (UInt128)2UL;
UInt128 y = x;
long timestamp = 0L; // reused for deadline checks.
while (true)
{
if (stopwatch.ElapsedTicks > budgetTicks)
timestamp = Stopwatch.GetTimestamp();
if (timestamp > deadlineTimestamp)
{
return false;
}
PerfectNumbers.Core/PrimeOrderCalculator.cs
+71 -41
View File
@@ -873,12 +873,12 @@ internal static partial class PrimeOrderCalculator
if (config.PollardRhoMilliseconds > 0 && pending.Count > 0)
{
Stopwatch stopwatch = Stopwatch.StartNew();
long budgetTicks = TimeSpan.FromMilliseconds(config.PollardRhoMilliseconds).Ticks;
long deadlineTimestamp = CreateDeadlineTimestamp(config.PollardRhoMilliseconds);
compositeStack = AcquireCompositeStack(Math.Max(pending.Count * 2, 4));
compositeStack.Push(remaining);
pending.Clear();
long timestamp = 0L; // reused for deadline checks.
while (compositeStack.Count > 0)
{
ulong composite = compositeStack.Pop();
@@ -894,13 +894,14 @@ internal static partial class PrimeOrderCalculator
continue;
}
if (stopwatch.ElapsedTicks > budgetTicks)
timestamp = Stopwatch.GetTimestamp();
if (timestamp > deadlineTimestamp)
{
pending.Add(composite);
continue;
}
if (!TryPollardRho(composite, stopwatch, budgetTicks, out ulong factor))
if (!TryPollardRho(composite, deadlineTimestamp, out ulong factor))
{
pending.Add(composite);
continue;
@@ -1143,48 +1144,77 @@ internal static partial class PrimeOrderCalculator
return true;
}
private static bool TryPollardRho(ulong n, Stopwatch stopwatch, long budgetTicks, out ulong factor)
{
factor = 0UL;
if ((n & 1UL) == 0UL)
{
factor = 2UL;
return true;
}
private static long CreateDeadlineTimestamp(int milliseconds)
{
if (milliseconds <= 0)
{
return long.MaxValue;
}
while (true)
{
if (stopwatch.ElapsedTicks > budgetTicks)
{
return false;
}
long stopwatchTicks = ConvertMillisecondsToStopwatchTicks(milliseconds);
long startTimestamp = Stopwatch.GetTimestamp();
long deadline = startTimestamp + stopwatchTicks;
if (deadline < startTimestamp)
{
return long.MaxValue;
}
ulong c = (DeterministicRandom.NextUInt64() % (n - 1UL)) + 1UL;
ulong x = (DeterministicRandom.NextUInt64() % (n - 2UL)) + 2UL;
ulong y = x;
ulong d = 1UL;
return deadline;
}
while (d == 1UL)
{
if (stopwatch.ElapsedTicks > budgetTicks)
{
return false;
}
private static long ConvertMillisecondsToStopwatchTicks(int milliseconds)
{
long frequency = Stopwatch.Frequency;
long baseTicks = (frequency / 1000L) * milliseconds;
long remainder = (frequency % 1000L) * milliseconds;
return baseTicks + (remainder / 1000L);
}
x = AdvancePolynomial(x, c, n);
y = AdvancePolynomial(y, c, n);
y = AdvancePolynomial(y, c, n);
ulong diff = x > y ? x - y : y - x;
d = BinaryGcd(diff, n);
}
private static bool TryPollardRho(ulong n, long deadlineTimestamp, out ulong factor)
{
factor = 0UL;
if ((n & 1UL) == 0UL)
{
factor = 2UL;
return true;
}
if (d != n)
{
factor = d;
return true;
}
}
}
long timestamp = 0L; // reused for deadline checks.
while (true)
{
timestamp = Stopwatch.GetTimestamp();
if (timestamp > deadlineTimestamp)
{
return false;
}
ulong c = (DeterministicRandom.NextUInt64() % (n - 1UL)) + 1UL;
ulong x = (DeterministicRandom.NextUInt64() % (n - 2UL)) + 2UL;
ulong y = x;
ulong d = 1UL;
while (d == 1UL)
{
timestamp = Stopwatch.GetTimestamp();
if (timestamp > deadlineTimestamp)
{
return false;
}
x = AdvancePolynomial(x, c, n);
y = AdvancePolynomial(y, c, n);
y = AdvancePolynomial(y, c, n);
ulong diff = x > y ? x - y : y - x;
d = BinaryGcd(diff, n);
}
if (d != n)
{
factor = d;
return true;
}
}
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private static ulong AdvancePolynomial(ulong x, ulong c, ulong modulus)