Should Julia guarantee semi-monotonic where appropriate (or even monotonic) math?

Internals & Design
1

Continuing the discussion from Formalizing Julia in Lean (and finding 400+ bugs in Base):

I see at the Java docs [see linked from the issue] even the sine function is guaranteed semi-monotonic… Semi-monotonic doesn’t imply correctly rounded I think i.e. it’s a stricter goal. I just discovered the non-monotonic bug and existence of semi- definition. Correctly rounding is a trade-off might be slower, not sure about semi-.

2

I think monotonic/semi-monotonic should be cheaper than correctly rounded (although it’s of course much harder for Float64 especially on multiple argument functions)