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Restore reviewed divisor heuristics

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Marek Lemańczyk committed 2025-10-24 19:50:32 +02:00
1 parent bbe0c02069
commit fab9ba0413
3 files changed
+9 -27
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PerfectNumbers.Core/Cpu/MersenneNumberDivisorByDivisorCpuTester.cs
+6 -14
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@@ -177,12 +177,6 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
bool lastIsSeven = (prime & 3UL) == 3UL;
const ushort DecimalMaskWhenLastIsSeven = (1 << 3) | (1 << 7) | (1 << 9);
const ushort DecimalMaskOtherwise = (1 << 1) | (1 << 3) | (1 << 9);
const byte AcceptableRemainder8Mask = 0b10000010;
const int NonZeroMod3Mask = 0b00000110;
const int NonZeroMod5Mask = 0b00011110;
const int NonZeroMod7Mask = 0b01111110;
const int NonZeroMod11Mask = 0b11111111110;
const int RequiredSmallPrimeMask = 0b1111;
while (divisor.CompareTo(limit) <= 0)
{
@@ -192,14 +186,12 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
ushort decimalMask = lastIsSeven ? DecimalMaskWhenLastIsSeven : DecimalMaskOtherwise;
bool admissible = ((decimalMask >> remainder10) & 1) != 0;
bool passesOctalMask = ((AcceptableRemainder8Mask >> remainder8) & 1) != 0;
int smallPrimeBits = ((NonZeroMod3Mask >> remainder3) & 1)
| (((NonZeroMod5Mask >> remainder5) & 1) << 1)
| (((NonZeroMod7Mask >> remainder7) & 1) << 2)
| (((NonZeroMod11Mask >> remainder11) & 1) << 3);
bool passesSmallPrimeMasks = (smallPrimeBits & RequiredSmallPrimeMask) == RequiredSmallPrimeMask;
if (admissible && passesOctalMask && passesSmallPrimeMasks)
if (admissible
&& (remainder8 == 1 || remainder8 == 7)
&& remainder3 != 0
&& remainder5 != 0
&& remainder7 != 0
&& remainder11 != 0)
{
MontgomeryDivisorData divisorData = MontgomeryDivisorData.FromModulus(candidate);
ulong divisorCycle;