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Narrow utf16 to ascii #39509

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pgovind
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@pgovind pgovind commented Jul 17, 2020

This is ready for review now.

NOTE: There is a bug here somewhere, but I can't seem to find it, so I'd appreciate another pair of eyes in this code. When I try to test this on WSL2, I get an error saying "Can't find file xunit.console.deps.json" when that file does in fact exist. The real error is that the xunit infra itself calls into the method being modified here and something goes wrong (maybe marshalling the path from string to native also uses this code? I'm not sure). AFAICT the changes are right.

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ghost commented Jul 23, 2020

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}
else if (AdvSimd.Arm64.IsSupported)
{
if (ContainsNonAsciiValue(AdvSimd.AddSaturate(utf16VectorFirst.AsUInt16(), asciiMaskForAddSaturate)))
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If I understand the original Sse2 algorithm right - this is testing if any of the characters in utf16VectorFirst is outside of [0, 0x7f] value range, right?

I don't think the algorithm on Arm64 should copy exactly, what Sse2 does.

I believe the following should be enough

AdvSimd.MaxPairwise(utf16VectorFirst.AsUInt16(), utf16VectorFirst.AsUInt16()).AsUInt64().ToScalar() & 0xFF80FF80FF80FF80UL != 0

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I agree.

}
else if (AdvSimd.Arm64.IsSupported)
{
utf16VectorFirst = AdvSimd.LoadVector128((short*)pUtf16Buffer);
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minor: add a comment // unaligned load

}
else if (AdvSimd.Arm64.IsSupported)
{
if (ContainsNonAsciiValue(AdvSimd.AddSaturate(utf16VectorFirst.AsUInt16(), asciiMaskForAddSaturate)))
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I agree.

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@pgovind I'm going to close this PR since this work is on hold. When we get back around to this work, we can create a fresh PR.

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7 participants