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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
View File
@@ -177,12 +177,6 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
bool lastIsSeven = (prime & 3UL) == 3UL; bool lastIsSeven = (prime & 3UL) == 3UL;
const ushort DecimalMaskWhenLastIsSeven = (1 << 3) | (1 << 7) | (1 << 9); const ushort DecimalMaskWhenLastIsSeven = (1 << 3) | (1 << 7) | (1 << 9);
const ushort DecimalMaskOtherwise = (1 << 1) | (1 << 3) | (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) while (divisor.CompareTo(limit) <= 0)
{ {
@@ -192,14 +186,12 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
ushort decimalMask = lastIsSeven ? DecimalMaskWhenLastIsSeven : DecimalMaskOtherwise; ushort decimalMask = lastIsSeven ? DecimalMaskWhenLastIsSeven : DecimalMaskOtherwise;
bool admissible = ((decimalMask >> remainder10) & 1) != 0; bool admissible = ((decimalMask >> remainder10) & 1) != 0;
bool passesOctalMask = ((AcceptableRemainder8Mask >> remainder8) & 1) != 0; if (admissible
int smallPrimeBits = ((NonZeroMod3Mask >> remainder3) & 1) && (remainder8 == 1 || remainder8 == 7)
| (((NonZeroMod5Mask >> remainder5) & 1) << 1) && remainder3 != 0
| (((NonZeroMod7Mask >> remainder7) & 1) << 2) && remainder5 != 0
| (((NonZeroMod11Mask >> remainder11) & 1) << 3); && remainder7 != 0
bool passesSmallPrimeMasks = (smallPrimeBits & RequiredSmallPrimeMask) == RequiredSmallPrimeMask; && remainder11 != 0)
if (admissible && passesOctalMask && passesSmallPrimeMasks)
{ {
MontgomeryDivisorData divisorData = MontgomeryDivisorData.FromModulus(candidate); MontgomeryDivisorData divisorData = MontgomeryDivisorData.FromModulus(candidate);
ulong divisorCycle; ulong divisorCycle;
PerfectNumbers.Core/MersenneDivisorCycles.cs
+2 -10
View File
@@ -58,11 +58,7 @@ public class MersenneDivisorCycles
return true; return true;
} }
const int InvalidParameterMask = 0b111; if (exponent <= 1UL || divisor <= 1UL || (divisor & 1UL) == 0UL)
int invalidBits = (exponent <= 1UL ? 1 : 0)
| ((divisor <= 1UL ? 1 : 0) << 1)
| ((int)(1UL ^ (divisor & 1UL)) << 2);
if ((invalidBits & InvalidParameterMask) != 0)
{ {
return false; return false;
} }
@@ -121,11 +117,7 @@ public class MersenneDivisorCycles
private static bool IsValidMersenneDivisorCandidate(ulong divisor, ulong exponent) private static bool IsValidMersenneDivisorCandidate(ulong divisor, ulong exponent)
{ {
const int InvalidParameterMask = 0b111; if (exponent <= 1UL || divisor <= 1UL || (divisor & 1UL) == 0UL)
int invalidBits = (exponent <= 1UL ? 1 : 0)
| ((divisor <= 1UL ? 1 : 0) << 1)
| ((int)(1UL ^ (divisor & 1UL)) << 2);
if ((invalidBits & InvalidParameterMask) != 0)
{ {
return false; return false;
} }
PerfectNumbers.Core/PrimeOrderCalculator.Cpu.cs
+1 -3
View File
@@ -188,9 +188,7 @@ internal static partial class PrimeOrderCalculator
private static ulong InitializeStartingOrderCpu(ulong prime, ulong phi, in MontgomeryDivisorData divisorData) private static ulong InitializeStartingOrderCpu(ulong prime, ulong phi, in MontgomeryDivisorData divisorData)
{ {
ulong order = phi; ulong order = phi;
const int AcceptablePrimeResidueMask = (1 << 1) | (1 << 7); if ((prime & 7UL) == 1UL || (prime & 7UL) == 7UL)
int residue = (int)(prime & 7UL);
if (((AcceptablePrimeResidueMask >> residue) & 1) != 0)
{ {
ulong half = phi >> 1; ulong half = phi >> 1;
if (Pow2EqualsOneCpu(half, prime, divisorData)) if (Pow2EqualsOneCpu(half, prime, divisorData))