Editorial review: Document remaining Wasm SIMD instructions by chrisdavidmills · Pull Request #43800 · mdn/content

chrisdavidmills · 2026-04-15T16:43:49Z

Description

This PR (hopefully!) documents all of the remaining Wasm SIMD instructions that were not covered in other PRs.

Motivation

Additional details

Related issues and pull requests

github-actions · 2026-04-15T16:45:34Z

Preview URLs (72 pages)

External URLs (12)

URL: /en-US/docs/WebAssembly/Reference/SIMD/arithmetic
Title: WebAssembly SIMD-specific arithmetic instructions

https://en.wikipedia.org/wiki/Saturation_arithmetic (2 times) (Note! This may be a new URL 👀)

URL: /en-US/docs/WebAssembly/Reference/SIMD/arithmetic/add_sat_s
Title: add_sat_s: Wasm SIMD arithmetic instruction

https://en.wikipedia.org/wiki/Saturation_arithmetic (1 time) (Note! This may be a new URL 👀)

URL: /en-US/docs/WebAssembly/Reference/SIMD/arithmetic/add_sat_u
Title: add_sat_u: Wasm SIMD arithmetic instruction

https://en.wikipedia.org/wiki/Saturation_arithmetic (1 time) (Note! This may be a new URL 👀)

URL: /en-US/docs/WebAssembly/Reference/SIMD/arithmetic/dot_i16x8_s
Title: dot_i16x8_s: Wasm SIMD arithmetic instruction

https://en.wikipedia.org/wiki/Dot_product (1 time) (Note! This may be a new URL 👀)

URL: /en-US/docs/WebAssembly/Reference/SIMD/arithmetic/q15mulr_sat_s
Title: q15mulr_sat_s: Wasm SIMD arithmetic instruction

https://en.wikipedia.org/wiki/Saturation_arithmetic (1 time) (Note! This may be a new URL 👀)

URL: /en-US/docs/WebAssembly/Reference/SIMD/arithmetic/sub_sat_s
Title: sub_sat_s: Wasm SIMD arithmetic instruction

https://en.wikipedia.org/wiki/Saturation_arithmetic (1 time) (Note! This may be a new URL 👀)

URL: /en-US/docs/WebAssembly/Reference/SIMD/arithmetic/sub_sat_u
Title: sub_sat_u: Wasm SIMD arithmetic instruction

https://en.wikipedia.org/wiki/Saturation_arithmetic (1 time) (Note! This may be a new URL 👀)

URL: /en-US/docs/WebAssembly/Reference/SIMD/conversion
Title: WebAssembly SIMD conversion instructions

https://en.wikipedia.org/wiki/Saturation_arithmetic (1 time) (Note! This may be a new URL 👀)

URL: /en-US/docs/WebAssembly/Reference/SIMD/conversion/trunc_sat_f32x4_s
Title: trunc_sat_f32x4_s: Wasm SIMD conversion instruction

https://en.wikipedia.org/wiki/Saturation_arithmetic (1 time) (Note! This may be a new URL 👀)

URL: /en-US/docs/WebAssembly/Reference/SIMD/conversion/trunc_sat_f32x4_u
Title: trunc_sat_f32x4_u: Wasm SIMD conversion instruction

https://en.wikipedia.org/wiki/Saturation_arithmetic (1 time) (Note! This may be a new URL 👀)

URL: /en-US/docs/WebAssembly/Reference/SIMD/conversion/trunc_sat_f64x2_s_zero
Title: trunc_sat_f64x2_s_zero: Wasm SIMD conversion instruction

https://en.wikipedia.org/wiki/Saturation_arithmetic (1 time) (Note! This may be a new URL 👀)

URL: /en-US/docs/WebAssembly/Reference/SIMD/conversion/trunc_sat_f64x2_u_zero
Title: trunc_sat_f64x2_u_zero: Wasm SIMD conversion instruction

https://en.wikipedia.org/wiki/Saturation_arithmetic (1 time) (Note! This may be a new URL 👀)

(comment last updated: 2026-04-21 07:09:03)

hamishwillee · 2026-04-16T23:51:52Z

+sidebar: webassemblysidebar
+---
+
+The **`add_sat_s`** [SIMD arithmetic instruction](/en-US/docs/WebAssembly/Reference/SIMD/arithmetic) performs a saturated addition of two signed [`v128`](/en-US/docs/WebAssembly/Reference/Types/v128) value interpretations. Each lane of the output value is the result of adding the corresponding lanes of the input value.


Not reviewing yet of course, but saw this term "saturated addition". I know this is probably known by the intended audience but I have never heard of this, and think it reasonable to be a wikipedia link

Edit note, if "Each lane of the output value is the result of adding the corresponding lanes of the input value." is all this means, I still wonder what "saturated" means. Probably not a wikipedia link if you can explain it here.

Good point. I've both linked to the relevant Wikipedia entry on the relevant pages and explained what the output values are clamped to due to the saturation.

…arest

…pages

…ording

…input type

…hould be signed

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Some SIMD fixes

chrisdavidmills · 2026-04-17T18:14:22Z

The tech review PR is merged (thanks, @eqrion!)

Over to you, @hamishwillee. Let me know if you can spot anything else that needs urgent attention before we get it merged.

hamishwillee

Looks pretty good. I have scanned this and tried to look at each type of function, but not necessarily each function in detail. Patterns are common, so if you take the suggestions in one you can roll them out to the similar methods.

hamishwillee

@chrisdavidmills Looks good. Just one comment to address https://github.com/mdn/content/pull/43800/changes/05cc6057b0b63a6b93052b648b8a17187cbecd5e..4de01b5317d01d470d6ef2ccf998ed0254ac6605#r3114060720

I'm approving so I don't block you after you have looked at that.

Document remaining Wasm SIMD instructions

603fc0a

chrisdavidmills requested a review from a team as a code owner April 15, 2026 16:43

chrisdavidmills requested review from hamishwillee and removed request for a team April 15, 2026 16:43

github-actions Bot added the Content:wasm WebAssembly docs label Apr 15, 2026

chrisdavidmills marked this pull request as draft April 15, 2026 16:44

github-actions Bot added the size/l [PR only] 501-1000 LoC changed label Apr 15, 2026

lots more arithmetic stuff

df1402f

github-actions Bot added size/xl [PR only] >1000 LoC changed and removed size/l [PR only] 501-1000 LoC changed labels Apr 16, 2026

hamishwillee reviewed Apr 16, 2026

View reviewed changes

chrisdavidmills added 2 commits April 17, 2026 10:13

Last SIMD instructions done

0ec5219

Explain saturation

b1566e2

chrisdavidmills marked this pull request as ready for review April 17, 2026 09:55

chrisdavidmills requested a review from a team as a code owner April 17, 2026 09:55

chrisdavidmills requested review from dipikabh and removed request for a team April 17, 2026 09:55

eqrion and others added 12 commits April 17, 2026 10:58

fix add_sat_u: description said signed but operation is unsigned

edd9e4b

fix store8_lane: binary example had 0x04 for align=1, should be 0x00

cfc2182

fix store16_lane: max alignment is 2, example should use align=2

7fe5e10

fix avgr_u: clarify it uses ceiling division, not generic round-to-ne…

fc6e674

…arest

fix pmin/pmax: describe asymmetric NaN propagation behavior

8b96dc6

fix conversion index: extend_low_i8x16 entries linked to extend_high …

249a87b

…pages

fix arithmetic index: avgr_u description had stale round-to-nearest w…

21515c7

…ording

fix narrow_u: inputs are signed; _u refers to saturation target, not …

dc1b10c

…input type

fix extend_low _u pages: lane ranges were copied from extend_high

7f01911

fix trunc_sat_f64x2_s_zero: saturation range described as unsigned, s…

bd1fa65

…hould be signed

Update files/en-us/webassembly/reference/simd/arithmetic/avgr_u/index.md

69fa009

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Merge pull request #15 from eqrion/simd-review-2

05cc605

Some SIMD fixes

chrisdavidmills changed the title ~~Document remaining Wasm SIMD instructions~~ Editorial review: Document remaining Wasm SIMD instructions Apr 17, 2026