SIMD narrowing and widening operations#2341
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tlively merged 2 commits intoWebAssembly:masterfrom Sep 14, 2019
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kripken
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Sep 13, 2019
| } | ||
| if (val < WideT(std::numeric_limits<T>::min())) { | ||
| return Literal(int32_t(std::numeric_limits<T>::min())); | ||
| } |
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could this code be simpler as
if (val > ..) val = ..::max()
else if (val < ..) val = ..::min()
return Literal(int32_t(val));
?
aheejin
approved these changes
Sep 13, 2019
| LaneArray<Lanes* 2> lanes = (vec.*IntoLanes)(); | ||
| LaneArray<Lanes> result; | ||
| for (size_t i = 0; i < Lanes; ++i) { | ||
| result[i] = lanes[(Side == LaneOrder::Low) ? i : i + Lanes]; |
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Does this handle sign/zero extension separately?
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The extension is handled by the IntoLanes template parameter. For example, when IntoLanes is getLanesSI8x16 the lanes are sign extended but when it is getLanesUI8x16 they are zero extended.
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| template<typename T> | ||
| Literal saturating_narrow( | ||
| typename TwiceWidth<typename std::make_signed<T>::type>::type val) { |
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Does this handle when val is an unsigned number that exceeds its signed version's max?
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The narrowing operations always treat the input lanes as signed, so this can't happen.
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As specified at https://github.com/WebAssembly/simd/blob/master/proposals/simd/SIMD.md#integer-to-integer-narrowing.