[kevingadd]

That kind of 'pack non-SIMD into SIMD, do SIMD op, unpack back into non-SIMD' thing tends to be slower than just doing non-SIMD ops in most cases.

You'd want to convert your non-SIMD data into a big stream of SIMD data up front, then do lots of operations on it, and then after that perhaps unpack it. Most SIMD scenarios just keep data in SIMD format indefinitely.

(Sometimes a compiler can use SIMD operations on arbitrary data by maintaining alignment requirements, etc. That sort of optimization might be possible for the JS runtime, but seems unlikely for anything other than typed arrays.)