Stream: git-wasmtime

Topic: wasmtime / PR #2302 Packed unsigned int to float conversion

Wasmtime GitHub notifications bot (Oct 19 2020 at 06:42):

jlb6740 edited PR #2302 from packed-convert-unsigned-int2 to main:

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Wasmtime GitHub notifications bot (Oct 21 2020 at 17:56):

jlb6740 requested cfallin, abrown, bnjbvr and julian-seward1 for a review on PR #2302.

Wasmtime GitHub notifications bot (Oct 28 2020 at 04:42):

cfallin submitted PR Review.

Wasmtime GitHub notifications bot (Oct 28 2020 at 04:42):

cfallin submitted PR Review.

Wasmtime GitHub notifications bot (Oct 28 2020 at 04:42):

cfallin created PR Review Comment:

s/converted/converting/

Wasmtime GitHub notifications bot (Oct 28 2020 at 04:42):

cfallin created PR Review Comment:

This is quite clever! A few questions:

• This all assumes 32x4, right? Do we also need to support 64x2 (converting into doubles rather than floats)? If not, can we add an assert (not just a debug assert; we should check in release too)?

• I was quite confused at first as I had thought (from this comment) that this was somehow using a 16-bit conversion rather than a 32-bit conversion with either the upper or lower 16 bits zeroed. I think it would be helpful to add some pseudocode or even ASCII art or something to illustrate what's going on -- for each lane, we basically have:

upper := (src & 0xffff0000) >> 1
lower := (src & 0x0000ffff)

dst := float(upper)*2 + float(lower)

which makes it a little easier to see the equivalence.

Wasmtime GitHub notifications bot (Oct 29 2020 at 23:45):

jlb6740 submitted PR Review.

Wasmtime GitHub notifications bot (Oct 29 2020 at 23:45):

jlb6740 created PR Review Comment:

This all assumes 32x4, right? Do we also need to support 64x2 (converting into doubles rather than floats)? If not, can we add an assert (not just a debug assert; we should check in release too)?

Yes, unsigned into float is only 32x4 for WASM. I can add a guard. Also I can add some additional comment/illustration to explain the algorithm better. :+1:

Wasmtime GitHub notifications bot (Oct 29 2020 at 23:47):

jlb6740 submitted PR Review.

Wasmtime GitHub notifications bot (Oct 29 2020 at 23:47):

jlb6740 created PR Review Comment:

@cfallin Also, this patch submitted as part of different patch set (branch) without realizing the impact. So patch merged yesterday so I'll address the comments in a separate patch from this one.

Wasmtime GitHub notifications bot (Oct 30 2020 at 00:21):

cfallin submitted PR Review.

Wasmtime GitHub notifications bot (Oct 30 2020 at 00:21):

cfallin created PR Review Comment:

Ah, OK, no worries and thanks!

Wasmtime GitHub notifications bot (Oct 30 2020 at 19:07):

jlb6740 closed without merge PR #2302.

Last updated: Dec 23 2024 at 12:05 UTC