Consistent results in calculations about handmademath HOT 8 CLOSED

Just chiming in to echo Martin's take here. I know this is an old topic and I've already said my 2 cents, but want to reiterate that the precision vs perf tradeoff here, even without considering platform dependent results, is no longer a good tradeoff considering how quick modern hardware does a real sqrt operation.

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Makes sense. To be honest I'm debating the merits of our hand-rolled SIMD code across the board. Certainly it doesn't seem worthwhile for small things like inverse square root.

I'll rework things to avoid specialized inverse square roots.

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Yep agreed. We should finally deal with this now with 2.0.

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Well to be clear, I'm suggesting we maybe just delete all our SIMD code. I'm not persuaded it's worth it. I mean maybe we could keep it for mat4 multiplies or something, but in general, I really doubt it's worth it. But SIMD is not my forte, so I'd defer to @mmozeiko on this one.

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It's fine to leave SIMD code if you want it. Just make sure scalar path matches SIMD float calculations. Doing SIMD on SSE & NEON will not break it, they produce same results. So SIMD by itself is not a problem.

Like for dot product that would be writing it as: return (x + z) + (y + w);

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Having a scalar mode is good for e.g. emscripten builds, but in general SIMD is a nice thing to keep. You don't need to SIMD everything though, and if the maintenance cost is high you can definitely simplify and have less SIMD implementation.

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You don't need to SIMD everything though, and if the maintenance cost is high you can definitely simplify and have less SIMD implementation.

I was looking at adding NOEN on a local branch yesterday, and was running some (very rudimentary, and not exhaustive) benchmarks. and it looks like SIMD is not worth it for Vec4 unless you care about debug performance, optimized builds at -O2 perform the same scalar vs SIMD. You do see an improvement for matrix transpose, need to add some benchmarks for other matrix ops, and Quaternions to see what else sees benefit. The same is true with both NEON and SSE, so If you wanted to remove some of the SIMD paths to simplify, its probably pretty safe to just use SIMD for matrices.

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I believe we should have consistent results between SIMD and non-SIMD code now. If you find any other inconsistencies, please let me know and I will reopen the issue.

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