The kind of things you can use direct SIMD for is a reasonably-different space than array languages; while some things can translate reasonably, APL-likes get m

The kind of things you can use direct SIMD for is a reasonably-different space than array languages; while some things can translate reasonably, APL-likes get much less pretty on operations where elements don't have homogeneous meaning/mapping, e.g.: the base64 conversion of OP. (for reference, I work on https://github.com/dzaima/CBQN https://github.com/dzaima/CBQN, an implementation of BQN, an APL derivative, and we have a DSL for implementing SIMD primitives for it (and sometimes scalar ones too): https://github.com/mlochbaum/Singeli https://github.com/mlochbaum/Singeli)