mlemanczyk/even-perfect-numbers-scanner
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Local variables optimized for reuse and lowered registry pressure.

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mlemanczyk committed 2025-10-12 23:57:58 +02:00
1 parent 77ef93eb91
commit 67dcf3ac7b
3 files changed
+208 -31
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PerfectNumbers.Core/MutableUInt128.cs
+33 -31
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@@ -80,23 +80,23 @@ public struct MutableUInt128
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public void Sub(ulong value)
{
ulong low = Low;
ulong result = low - value;
ulong borrow = result > low ? 1UL : 0UL;
ulong temp = Low;
ulong result = temp - value;
temp = result > temp ? 1UL : 0UL;
Low = result;
High -= borrow;
High -= temp;
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public void Sub(MutableUInt128 value)
{
ulong low = Low;
ulong result = low - value.Low;
ulong borrow = low < value.Low ? 1UL : 0UL;
ulong temp = Low;
ulong result = temp - value.Low;
temp = temp < value.Low ? 1UL : 0UL;
Low = result;
High = High - value.High - borrow;
High = High - value.High - temp;
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -105,34 +105,34 @@ public struct MutableUInt128
ulong currentHigh = High;
ulong currentLow = Low;
ulong carry = Mul64(currentLow, value, out ulong newLow);
Mul64(currentHigh, value, out ulong shiftedHigh);
ulong newHigh = shiftedHigh + carry;
ulong temp = Mul64(currentLow, value, out currentLow);
Mul64(currentHigh, value, out currentHigh);
temp += currentHigh;
Low = newLow;
High = newHigh;
Low = currentLow;
High = temp;
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private static ulong Mul64(ulong left, ulong right, out ulong low)
public static ulong Mul64(ulong left, ulong right, out ulong low)
{
const ulong Mask32 = 0xFFFF_FFFFUL;
ulong leftLow = left & Mask32;
ulong leftHigh = left >> 32;
ulong rightLow = right & Mask32;
ulong rightHigh = right >> 32;
ulong leftLow = left & Mask32;
ulong lowLow = leftLow * rightLow;
ulong lowHigh = leftLow * rightHigh;
ulong highLow = leftHigh * rightLow;
ulong highHigh = leftHigh * rightHigh;
ulong temp = right >> 32;
leftLow *= temp;
rightLow *= leftHigh;
leftHigh *= temp;
ulong carry = (lowLow >> 32) + (lowHigh & Mask32) + (highLow & Mask32);
ulong high = highHigh + (lowHigh >> 32) + (highLow >> 32) + (carry >> 32);
temp = (lowLow >> 32) + (leftLow & Mask32) + (rightLow & Mask32);
leftHigh += (leftLow >> 32) + (rightLow >> 32) + (temp >> 32);
low = ((carry & Mask32) << 32) | (lowLow & Mask32);
return high;
low = ((temp & Mask32) << 32) | (lowLow & Mask32);
return leftHigh;
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -182,22 +182,24 @@ public struct MutableUInt128
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public readonly ulong Mod(ulong modulus)
{
if (modulus == 0UL)
{
throw new DivideByZeroException();
}
{
// This case will never happen in production code.
// if (modulus == 0UL)
// {
// throw new DivideByZeroException();
// }
if (High == 0UL)
ulong high = High;
if (high == 0UL)
{
return Low % modulus;
}
MutableUInt128 remainder = default;
int highBitLength = 64 - BitOperations.LeadingZeroCount(High);
int highBitLength = 64 - BitOperations.LeadingZeroCount(high);
if (highBitLength > 0)
{
ProcessWord(ref remainder, High, highBitLength, modulus);
ProcessWord(ref remainder, high, highBitLength, modulus);
}
ProcessWord(ref remainder, Low, 64, modulus);