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Clean up Guid.DecodeByte #88267

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Merged
merged 2 commits into from
Jun 30, 2023
Merged

Clean up Guid.DecodeByte #88267

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282ab8c
Clean up Guid.DecodeByte
EgorBo Jun 30, 2023
82e0d69
cleanup
EgorBo Jun 30, 2023
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24 changes: 7 additions & 17 deletions src/libraries/System.Private.CoreLib/src/System/Guid.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -727,27 +727,17 @@ private static bool TryParseExactX(ReadOnlySpan<char> guidString, ref GuidResult
}

[MethodImpl(MethodImplOptions.AggressiveInlining)]
private static byte DecodeByte(nuint ch1, nuint ch2, ref int invalidIfNegative)
private static byte DecodeByte(char ch1, char ch2, ref int invalidIfNegative)
{
// TODO https://github.com/dotnet/runtime/issues/13464:
// Replace the Unsafe.Add with HexConverter.FromChar once the bounds checks are eliminated.

ReadOnlySpan<byte> lookup = HexConverter.CharToHexLookup;
Debug.Assert(lookup.Length == 256);

int h1 = -1;
if (ch1 < (nuint)lookup.Length)
{
h1 = (sbyte)Unsafe.Add(ref MemoryMarshal.GetReference(lookup), (nint)ch1);
}
h1 <<= 4;

int h2 = -1;
if (ch2 < (nuint)lookup.Length)
{
h2 = (sbyte)Unsafe.Add(ref MemoryMarshal.GetReference(lookup), (nint)ch2);
}
int upper = (sbyte)lookup[(byte)ch1];
int lower = (sbyte)lookup[(byte)ch2];
int result = (upper << 4) | lower;

int result = h1 | h2;
// Result will be negative if ch1 or/and ch2 are greater than 0xFF
result = (ch1 | ch2) >> 8 == 0 ? result : -1;
invalidIfNegative |= result;
return (byte)result;
}
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