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Use internal BitOperations.ResetLowestSetBit #87798

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merged 4 commits into from
Jun 22, 2023
Merged

Use internal BitOperations.ResetLowestSetBit #87798

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fc0695f
Use internal `BitOperations.ResetLowestSetBit`
xtqqczze Jun 20, 2023
16c19e0
fixup
xtqqczze Jun 20, 2023
3989e4d
fixup
xtqqczze Jun 20, 2023
887ccac
Use `uint.TrailingZeroCount`
xtqqczze Jun 20, 2023
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24 changes: 4 additions & 20 deletions src/libraries/System.Private.CoreLib/src/System/Globalization/Ordinal.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -462,8 +462,7 @@ ref Unsafe.Add(ref valueRef, 1), valueTailLength))
// Do a full IgnoreCase equality comparison. SpanHelpers.IndexOf skips comparing the two characters in some cases,
// but we don't actually know that the two characters are equal, since we compared with | 0x20. So we just compare
// the full string always.
int bitPos = BitOperations.TrailingZeroCount(mask);
nint charPos = (nint)((uint)bitPos / 2); // div by 2 (shr) because we work with 2-byte chars
nint charPos = (nint)(uint.TrailingZeroCount(mask) / sizeof(ushort));
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Suggested change
nint charPos = (nint)(uint.TrailingZeroCount(mask) / sizeof(ushort));
nint charPos = (nint)(uint.TrailingZeroCount(mask) / sizeof(char));

@stephentoub This would be slightly clearer, but might not be worth spinning CI again?

if (EqualsIgnoreCase(ref Unsafe.Add(ref searchSpace, offset + charPos), ref valueRef, value.Length))
{
// Match! Return the index.
Expand All @@ -472,14 +471,7 @@ ref Unsafe.Add(ref valueRef, 1), valueTailLength))

// Clear the two lowest set bits in the mask. If there are no more set bits, we're done.
// If any remain, we loop around to do the next comparison.
if (Bmi1.IsSupported)
{
mask = Bmi1.ResetLowestSetBit(Bmi1.ResetLowestSetBit(mask));
}
else
{
mask &= ~(uint)(0b11 << bitPos);
}
mask = BitOperations.ResetLowestSetBit(BitOperations.ResetLowestSetBit(mask));
} while (mask != 0);
goto LoopFooter;

Expand Down Expand Up @@ -536,8 +528,7 @@ ref Unsafe.Add(ref valueRef, 1), valueTailLength))
// Do a full IgnoreCase equality comparison. SpanHelpers.IndexOf skips comparing the two characters in some cases,
// but we don't actually know that the two characters are equal, since we compared with | 0x20. So we just compare
// the full string always.
int bitPos = BitOperations.TrailingZeroCount(mask);
int charPos = (int)((uint)bitPos / 2); // div by 2 (shr) because we work with 2-byte chars
nint charPos = (nint)(uint.TrailingZeroCount(mask) / sizeof(ushort));
if (EqualsIgnoreCase(ref Unsafe.Add(ref searchSpace, offset + charPos), ref valueRef, value.Length))
{
// Match! Return the index.
Expand All @@ -546,14 +537,7 @@ ref Unsafe.Add(ref valueRef, 1), valueTailLength))

// Clear the two lowest set bits in the mask. If there are no more set bits, we're done.
// If any remain, we loop around to do the next comparison.
if (Bmi1.IsSupported)
{
mask = Bmi1.ResetLowestSetBit(Bmi1.ResetLowestSetBit(mask));
}
else
{
mask &= ~(uint)(0b11 << bitPos);
}
mask = BitOperations.ResetLowestSetBit(BitOperations.ResetLowestSetBit(mask));
} while (mask != 0);
goto LoopFooter;

Expand Down
18 changes: 4 additions & 14 deletions src/libraries/System.Private.CoreLib/src/System/SpanHelpers.Char.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -114,9 +114,7 @@ ref Unsafe.As<char, byte>(ref Unsafe.Add(ref searchSpace, offset + 1)),
uint mask = cmpAnd.ExtractMostSignificantBits();
do
{
int bitPos = BitOperations.TrailingZeroCount(mask);
// div by 2 (shr) because we work with 2-byte chars
nint charPos = (nint)((uint)bitPos / 2);
nint charPos = (nint)(uint.TrailingZeroCount(mask) / sizeof(ushort));
if (valueLength == 2 || // we already matched two chars
SequenceEqual(
ref Unsafe.As<char, byte>(ref Unsafe.Add(ref searchSpace, offset + charPos)),
Expand All @@ -126,10 +124,7 @@ ref Unsafe.As<char, byte>(ref value), (nuint)(uint)valueLength * 2))
}

// Clear two the lowest set bits
if (Bmi1.IsSupported)
mask = Bmi1.ResetLowestSetBit(Bmi1.ResetLowestSetBit(mask));
else
mask &= ~(uint)(0b11 << bitPos);
mask = BitOperations.ResetLowestSetBit(BitOperations.ResetLowestSetBit(mask));
} while (mask != 0);
goto LOOP_FOOTER;

Expand Down Expand Up @@ -181,9 +176,7 @@ ref Unsafe.As<char, byte>(ref value), (nuint)(uint)valueLength * 2))
uint mask = cmpAnd.ExtractMostSignificantBits();
do
{
int bitPos = BitOperations.TrailingZeroCount(mask);
// div by 2 (shr) because we work with 2-byte chars
int charPos = (int)((uint)bitPos / 2);
nint charPos = (nint)(uint.TrailingZeroCount(mask) / sizeof(ushort));
if (valueLength == 2 || // we already matched two chars
SequenceEqual(
ref Unsafe.As<char, byte>(ref Unsafe.Add(ref searchSpace, offset + charPos)),
Expand All @@ -193,10 +186,7 @@ ref Unsafe.As<char, byte>(ref value), (nuint)(uint)valueLength * 2))
}

// Clear two lowest set bits
if (Bmi1.IsSupported)
mask = Bmi1.ResetLowestSetBit(Bmi1.ResetLowestSetBit(mask));
else
mask &= ~(uint)(0b11 << bitPos);
mask = BitOperations.ResetLowestSetBit(BitOperations.ResetLowestSetBit(mask));
} while (mask != 0);
goto LOOP_FOOTER;

Expand Down