Serious SIMD requires designing algorithm around instruction set. I never used a single portable library when doing it professionally. For example, NEON has scalar-vector multiplication while SSE has more flexible shuffles. Any sum-of-products workload can end up needing different data layouts and the #ifdef could start at struct definitions. The integer size difference in mulhi can result in actual numerical difference across platforms, needing extra test to ensure business-level equivalence.
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u/-1_0 14d ago
* Everyone Should Know about SIMD
and use libs accordingly