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Simplify prime guards and adopt unified mulmod

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Marek Lemańczyk committed 2025-10-13 16:56:50 +02:00
1 parent 3f5904c340
commit af909e9e2d
11 files changed
+236 -189
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PerfectNumbers.Core/ULongExtensions.cs
+16 -25
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@@ -290,26 +290,17 @@ public static class ULongExtensions
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
// TODO: Replace this fallback with the UInt128 Montgomery helper measured fastest in
// MulMod64Benchmarks so CPU callers stop paying for triple modulo operations.
public static ulong MulMod64(this ulong a, ulong b, ulong modulus) => (ulong)(UInt128)(((a % modulus) * (b % modulus)) % modulus);
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static ulong MulMod64GpuCompatible(this ulong a, ulong b, ulong modulus)
public static ulong MulMod64(this ulong a, ulong b, ulong modulus)
{
// TODO: Remove this GPU-compatible shim from production once callers migrate to MulMod64,
// which the benchmarks show is roughly 6-7× faster on dense 64-bit inputs.
GpuUInt128 state = new(a % modulus);
return state.MulMod(b, modulus);
}
if (modulus <= 1UL)
{
return 0UL;
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static ulong MulMod64GpuCompatibleDeferred(this ulong a, ulong b, ulong modulus)
{
// TODO: Move this deferred helper to the benchmark suite; the baseline MulMod64 avoids the
// 5-40× slowdown seen across real-world operand distributions.
GpuUInt128 state = new(a);
return state.MulModWithNativeModulo(b, modulus);
ulong reducedA = a >= modulus ? a % modulus : a;
ulong reducedB = b >= modulus ? b % modulus : b;
GpuUInt128 state = new(reducedA);
return state.MulMod(reducedB, modulus);
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -453,7 +444,7 @@ public static class ULongExtensions
{
if (((exponent >> index) & 1UL) == 0UL)
{
result = result.MulMod64GpuCompatible(result, modulus);
result = result.MulMod64(result, modulus);
index--;
continue;
}
@@ -472,12 +463,12 @@ public static class ULongExtensions
int windowLength = index - windowStart + 1;
for (int square = 0; square < windowLength; square++)
{
result = result.MulMod64GpuCompatible(result, modulus);
result = result.MulMod64(result, modulus);
}
ulong windowValue = (exponent >> windowStart) & ((1UL << windowLength) - 1UL);
int tableIndex = (int)((windowValue - 1UL) >> 1);
result = result.MulMod64GpuCompatible(oddPowers.Get(tableIndex), modulus);
result = result.MulMod64(oddPowers.Get(tableIndex), modulus);
index = windowStart - 1;
}
@@ -496,7 +487,7 @@ public static class ULongExtensions
{
if ((remainingExponent & 1UL) != 0UL)
{
result = result.MulMod64GpuCompatible(baseValue, modulus);
result = result.MulMod64(baseValue, modulus);
}
remainingExponent >>= 1;
@@ -505,7 +496,7 @@ public static class ULongExtensions
break;
}
baseValue = baseValue.MulMod64GpuCompatible(baseValue, modulus);
baseValue = baseValue.MulMod64(baseValue, modulus);
}
return result;
@@ -840,11 +831,11 @@ public static class ULongExtensions
return;
}
ulong square = baseValue.MulMod64GpuCompatible(baseValue, modulus);
ulong square = baseValue.MulMod64(baseValue, modulus);
ulong current = baseValue;
for (int i = 1; i < _count; i++)
{
current = current.MulMod64GpuCompatible(square, modulus);
current = current.MulMod64(square, modulus);
SetValue(i, current);
}
}