On: How close can pure functional programming get to C?

[gobdovan]

Have you considered exposing these optimisations through a library so programmers can request optimisation passes and have the compiler check the preconditions?

Asking cuz I'm preparing an article on how fast JS can get and found the same thing, you can get in 10% of optimised C-code with basically any code if you torture V8 enough (excepting SIMD where there seems to be a bug in V8 where it doesn't optimise to SIMD even when beyond obvious). Figured out I could extract it in a lib and do it more streamlined but not sure how well manual transforms generalise.

Also, when working on the roc-deflate, did you find recurring transformations that could fit that model or were most improvements specific to compression?

[countWSS → gobdovan]

IIRC in weird corner cases, JS code can outperform wasm/C/C++ because JIT optimizes with escape analysis/inlining.

>where it doesn't optimise to SIMD even when beyond obvious What was that code?

[gobdovan → countWSS]

Yes, it does beat -O3 C sometimes. I took code from diverse 'language speed' benchmarks from the internet and had to rearrange them to get -O3 to beat equivalent-looking JS (Node 25.8.1 w\ V8 14.1 and clang 21 on MBP3).

> What was that code?

literally:

``` function numericKernel(a, b, out, n) {

    for (let i = 0; i < n; i += 4) {

        out[i]     = a[i]     * b[i]     + 0.25;
        out[i + 1] = a[i + 1] * b[i + 1] + 0.25;
        out[i + 2] = a[i + 2] * b[i + 2] + 0.25;
        out[i + 3] = a[i + 3] * b[i + 3] + 0.25;

    }

} ```

[countWSS → gobdovan]

i've tried various options, Firefox prefers ` for (let i = n; i--;) out[i] = a[i] * b[i] + 0.25;` Its already at peak optimization so no form is significantly better.