mlemanczyk/even-perfect-numbers-scanner
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Restore Math.Sqrt heuristic bound

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Marek Lemańczyk committed 2025-10-29 01:43:12 +01:00
1 parent 5a9e103bd5
commit f49963c4f6
2 files changed
+26 -42
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PerfectNumbers.Core/HeuristicCombinedPrimeTester.cs
+13 -21
View File
@@ -306,33 +306,25 @@ Cleanup:
internal static ulong ComputeHeuristicSqrt(ulong n)
{
if (n < 2UL)
ulong sqrt = (ulong)Math.Sqrt(n);
UInt128 square = (UInt128)sqrt * sqrt;
while (square > n)
{
return n;
sqrt--;
square = (UInt128)sqrt * sqrt;
}
int log2 = BitOperations.Log2(n);
ulong estimate = 1UL << ((log2 + 1) >> 1);
ulong quotient = n / estimate;
while (estimate > quotient)
ulong next = sqrt + 1UL;
UInt128 nextSquare = (UInt128)next * next;
while (nextSquare <= n)
{
estimate = (estimate + quotient) >> 1;
quotient = n / estimate;
sqrt = next;
next++;
nextSquare = (UInt128)next * next;
}
while (true)
{
ulong nextEstimate = estimate + 1UL;
if (nextEstimate > n / nextEstimate)
{
break;
}
estimate = nextEstimate;
}
return estimate;
return sqrt;
}
private static ReadOnlySpan<uint> GetCombinedDivisors(byte nMod10)
PerfectNumbers.Core/HeuristicPrimeTester.cs
+13 -21
View File
@@ -431,33 +431,25 @@ Cleanup:
internal static ulong ComputeHeuristicSqrt(ulong n)
{
if (n < 2UL)
ulong sqrt = (ulong)Math.Sqrt(n);
UInt128 square = (UInt128)sqrt * sqrt;
while (square > n)
{
return n;
sqrt--;
square = (UInt128)sqrt * sqrt;
}
int log2 = BitOperations.Log2(n);
ulong estimate = 1UL << ((log2 + 1) >> 1);
ulong quotient = n / estimate;
while (estimate > quotient)
ulong next = sqrt + 1UL;
UInt128 nextSquare = (UInt128)next * next;
while (nextSquare <= n)
{
estimate = (estimate + quotient) >> 1;
quotient = n / estimate;
sqrt = next;
next++;
nextSquare = (UInt128)next * next;
}
while (true)
{
ulong nextEstimate = estimate + 1UL;
if (nextEstimate > n / nextEstimate)
{
break;
}
estimate = nextEstimate;
}
return estimate;
return sqrt;
}
private static ReadOnlySpan<byte> GetGroupBEndingOrder(byte nMod10) => nMod10 switch