The list of arguments to _mm512_setr_epi64 are just reciprocals of powers of 10, multiplied by 2^52. The scalar code uses division by powers of 10, which'd comp

The list of arguments to _mm512_setr_epi64 are just reciprocals of powers of 10, multiplied by 2^52. The scalar code uses division by powers of 10, which'd compile down to similar multiplication constants; you just don't see them because the compiler does that for the scalar code, but you have to do so manually for AVX-512. And permb_const is a list of indices for the result characters within the vector register - the algorithm works on 64-bit integers, but the result must be a list of bytes, so it picks out every 8th one.