WebAssembly / WebAssembly/half-precision
f16x8.demote_f64x2_zero
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- Dominant language
- WebAssembly
- Stars
- 14
- Forks
- 0
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Description
Do we need direct conversion from F64 lanes to F16?
Recently, we discovered there is pure support on x64 for direct f64 -> f16 conversion.
F64 to F16 conversion with roundToEven semantic couldn't be efficiently implemented on x64 without AVX512-FP16(so, only Sapphire Rapids Xeon support it today).
We can introduce f16x8.demote_f64x2_zero with roundToZero rounding, so it will be composable with f64 -> f32 -> f16 conversions, but today roundToEven semantic is a default on the Web and such instruction could be easily emulated with f32x4.demote_f64x2_zero + f16x8.demote_f32x4_zero
On the other side Arm64 supports direct F64 -> F16 conversion with roundToEven rounding mode, but without f16x8.demote_f64x2_zero it won't be possible to use it.
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by reviewing the proposal discussion and the linked TC39 float16 issue to understand the competing rounding semantics and platform support described here. Define whether a direct f16x8.demote_f64x2_zero operation is needed and what agreement would establish the issue as resolved; no implementation files or tests are named.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- wasm
- Domain
- compilers
- Issue type
- Feature
- Difficulty
- 5/5
- Estimated time
- Over a week
- Activity status
- Stale
- Clarity
- Needs clarification
- Newbie friendliness
- 25/100