Attached is a quick-and-dirty attempt to add MSVC support for the rightmost/leftmost-one-pos functions.
0001 adds asserts to the existing coding.
0002 adds MSVC support. Tests pass on CI, but it's of course possible that there is some bug that prevents hitting the fastpath. I've mostly used the platform specific types, so some further cleanup might be needed.
0003 tries one way to reduce the duplication that arose in 0002. Maybe there is a better way.
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