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Replace small-modulo uses with optimized helpers

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Marek Lemańczyk committed 2025-09-22 19:54:50 +02:00
1 parent ca866ffc5b
commit 3598f88aaf
9 files changed
+46 -38
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PerfectNumbers.Core/MersenneNumberTester.cs
+7 -7
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@@ -67,7 +67,7 @@ public sealed class MersenneNumberTester(
for (; k <= limit; k++)
{
q = twoP * k + UInt128.One;
remainder = (ulong)(q % 10UL);
remainder = q.Mod10();
bool shouldCheck = lastIsSeven
? remainder == 7UL || remainder == 9UL || remainder == 3UL
: remainder == 1UL || remainder == 3UL || remainder == 9UL;
@@ -75,12 +75,12 @@ public sealed class MersenneNumberTester(
// Early modular filters for odd order and small-prime rejections
if (shouldCheck)
{
ulong mod8 = (ulong)(q % 8UL);
ulong mod8 = q.Mod8();
if (mod8 != 1UL && mod8 != 7UL)
{
continue;
}
else if ((ulong)(q % 3UL) == 0UL || (ulong)(q % 5UL) == 0UL)
else if (q.Mod3() == 0UL || q.Mod5() == 0UL)
{
continue;
}
@@ -106,7 +106,7 @@ public sealed class MersenneNumberTester(
for (; k2 <= limit; k2++)
{
q2 = twoP * k2 + 1UL;
remainder2 = (ulong)(q2 % 10UL);
remainder2 = q2.Mod10();
bool shouldCheck2 = lastIsSeven
? remainder2 == 7UL || remainder2 == 9UL || remainder2 == 3UL
: remainder2 == 1UL || remainder2 == 3UL || remainder2 == 9UL;
@@ -114,12 +114,12 @@ public sealed class MersenneNumberTester(
// Early modular filters for odd order and small-prime rejections
if (shouldCheck2)
{
ulong mod8 = (ulong)(q2 % 8UL);
ulong mod8 = q2.Mod8();
if (mod8 != 1UL && mod8 != 7UL)
{
shouldCheck2 = false;
}
else if ((ulong)(q2 % 3UL) == 0UL || (ulong)(q2 % 5UL) == 0UL)
else if (q2.Mod3() == 0UL || q2.Mod5() == 0UL)
{
shouldCheck2 = false;
}
@@ -203,7 +203,7 @@ public sealed class MersenneNumberTester(
{
// Safe early rejections using known orders for tiny primes:
// 7 | M_p iff 3 | p. Avoid rejecting p == 3 where M_3 == 7 is prime.
if (exponent % 3UL == 0UL && exponent != 3UL)
if (exponent.Mod3() == 0UL && exponent != 3UL)
{
return false;
}