mlemanczyk/even-perfect-numbers-scanner
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Document unreachable MulMod guards

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Marek Lemańczyk committed 2025-10-20 11:48:07 +02:00
1 parent 34240ab3e9
commit 94323c2e8c
2 files changed
+26 -26
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PerfectNumbers.Core/UInt128Extensions.cs
+11 -14
View File
@@ -671,10 +671,11 @@ public static class UInt128Extensions
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static UInt128 AddMod(this UInt128 value, UInt128 addend, UInt128 modulus)
{
if (modulus <= UInt128.One)
{
return UInt128.Zero;
}
// The by-divisor CPU path never supplies moduli below 2, so this guard stays disabled.
// if (modulus <= UInt128.One)
// {
// return UInt128.Zero;
// }
value %= modulus;
addend %= modulus;
@@ -684,21 +685,17 @@ public static class UInt128Extensions
}
UInt128 threshold = modulus - addend;
if (value >= threshold)
{
return value - threshold;
}
return value + addend;
return value >= threshold ? value - threshold : value + addend;
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static UInt128 SubtractOneMod(this UInt128 value, UInt128 modulus)
{
if (modulus <= UInt128.One)
{
return UInt128.Zero;
}
// The divisor scan never observes moduli below 2, so leave this guard documented but inactive.
// if (modulus <= UInt128.One)
// {
// return UInt128.Zero;
// }
if (value == UInt128.Zero)
{
PerfectNumbers.Core/ULongExtensions.cs
+15 -12
View File
@@ -458,10 +458,11 @@ public static partial class ULongExtensions
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static ulong AddMod64(this ulong value, ulong addend, ulong modulus)
{
if (modulus <= 1UL)
{
return 0UL;
}
// The CPU factoring path never presents moduli below 2, so leave this guard documented but disabled.
// if (modulus <= 1UL)
// {
// return 0UL;
// }
UInt128 sum = (UInt128)value + addend;
UInt128 mod = modulus;
@@ -480,10 +481,11 @@ public static partial class ULongExtensions
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private static ulong FoldMontgomery(ulong value, ulong modulus)
{
if (modulus <= 1UL)
{
return 0UL;
}
// Moduli in the divisor scan always exceed 1, so retain the documentation and skip the runtime guard.
// if (modulus <= 1UL)
// {
// return 0UL;
// }
if (value < modulus)
{
@@ -508,10 +510,11 @@ public static partial class ULongExtensions
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static ulong ModPow64(this ulong value, ulong exponent, ulong modulus)
{
if (modulus <= 1UL)
{
return 0UL;
}
// Moduli below 2 do not occur in the even-perfect divisor scans, so keep the guard commented for clarity.
// if (modulus <= 1UL)
// {
// return 0UL;
// }
ulong result = 1UL;
value = FoldMontgomery(value, modulus);