Presently, I'm implementing operations for a WASM emulator/runtime, so it's more a case of transitively acquiring use cases from WASM, though I'm also doing this specifically to practice accomplishing useful things with the vector API.
Regarding saturating arithmetic: WASM has operations for that as well (both signed and unsigned), so on that basis alone it would be a welcome addition as far as I'm concerned. FWIW, another simple use case for saturating arithmetic is audio processing/mixing (when processing many channels at once) because saturation closely matches analog clipping, and also perhaps image compositing for similar reasons. On Thu, Apr 18, 2024 at 1:40 PM Paul Sandoz <paul.san...@oracle.com> wrote: > Hi David, > > It’s not at all outlandish, but would caution it's more work than one > might initially think. > > Could you describe a little more about your use case? that can be helpful > to understand the larger picture and demand. Using unsigned comparison > would be my recommended approach with the current API. CC'ing Sandhya for > her opinion. > > Generally when we add new Vector operations we also consider the impact on > the scalar types and try to fill any gaps there, so the vector operation > behavior is composed from the scalar operation behavior (so like you > indicated regarding symmetry). > > We are seeing demand for saturated arithmetic primarily for vector (not > “vector” as in hardware vector) search, so we may do something there for > specific integral types. > > Paul. > > > On Apr 17, 2024, at 7:13 AM, David Lloyd <david.ll...@redhat.com> wrote: > > > > I've been trying the the incubating Vector API and one thing I've missed > on integer-typed vectors is having unsigned min/max operations. There is a > signed min/max operation, and unsigned comparison, but no unsigned min/max. > > > > I guess this is for symmetry with `Math`, which only has signed > `min`/`max`. However, I would point out that while it's not very hard to > implement one's own unsigned min/max for integer types using > `compareUnsigned`, it is a bit harder to do so with vectors. The best I've > come up with is to take one of two approaches: > > > > 1. Zero-extend the vector to the next-larger size, perform the min/max, > and reduce it back down again, or > > 2. Add <IntType>.MIN_VALUE, min/max with a value or vector also offset > by <IntType>.MIN_VALUE, and then subtract the offset again > > > > I guess a third approach could be to do a comparison using unsigned > compares, and then use the resultant vector mask to select items from the > original two vectors, but I didn't bother to work out this solution given I > already had the other two options. > > > > Would it be feasible to add unsigned min/max operations for vectors? It > looks like at least AArch64 has support for this as a single instruction, > so it doesn't seem too outlandish. > > > > And as a separate (but related) question, what about > `Math.minUnsigned`/`Math.maxUnsigned` of `int` and `long` for symmetry? > > > > -- > > - DML • he/him > > -- - DML • he/him
