The tests and notebooks maybe: not the unrolling and re-architecting to use masking SIMD-ification. I used to do SIMD stuff a lot over the last 17 years, and it would have taken me probably a day to do that (convert 7 algorithms, all with support for various wrapping/mirroring/clamping extent-handling, so around 800 raw source file lines of templated C++) to use SIMD - and well.

Then it probably would have taken me at least half a day to think about what tests to write and to make them.

It did it in around 5 minutes. I had to check it, and it wasn't perfect, but it compiled, ran, and was very close.