Comment author: @nojb

I'm not an expert on IEEE754, but it sounds like a potentially useful addition. Would you like to open a PR on https://github.com/ocaml/ocaml to discuss your code?

FP rounding mode is another piece of global state, and I don't feel like exposing this to casual users. I'd rather leave that to a specialized, external library. Even better would be a more functional API that hides the global state. Again such an API could be developed first as an external library.

In case this is of interest, the Interval library does this (internally).

Yes, interval arithmetic is a great example of a nice, high-level, declarative API that changes rounding mode internally in the implementation.

Actually I wonder whether there are any other common use of non-default rounding modes beyond interval arithmetic.

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