Add support for MidpointRounding on Math.Round

[sWW26]

Description

It would be good to be able to use the MidpointRounding option with Math.Round. It looks like big.js supports it & I think its the default for Math.round in JS too?

Repro code

https://fable.io/repl3/#?code=PYBwpgdgBAygngZwC5gLYFgBQWA2YlQAmYAxgJaoCGOASmAgK44EC8UAspUgBYB0NwBhEIAKAEy8ArOwA0UAAxz2ZQiGBkISAUMIaA5rwCCAd0pwAYgCdgqAFphrASigB6F1ATdBOQlABGYFAAzHJ6ZABu9FBiuPhQAGY4wFx0jMxQbJw8-ILC4lJyihwqahpauboQBiZmVjb2Tq7unt6+AcGhEVExmABC1sYIDrwAIja8JMAQCMB4vEl6RKQU1KlMSFj9wIPDY6gTUzNzCwlJKfTrQA&html=Q&css=Q

Expected and actual results

Math.Round(1.5M, 0, MidpointRounding.AwayFromZero) = 2
Math.Round(1.5, 0, MidpointRounding.AwayFromZero) = 2
Math.Round(2.5M, 0, MidpointRounding.AwayFromZero) = 3
Math.Round(2.5, 0, MidpointRounding.AwayFromZero) = 3

[alfonsogarciacaro]

Hi @sWW26! Sorry for the late reply, I had a quick look at this and although it looks easy to solve, there are different things we need to do for proper support: deal with different overloads, MidpointRounding enum also has other cases, I couldn't find a "recommended" way to do half-up rounding in JS... so it may take some time. Of course any help to fix this is welcome!

[sWW26]

After a bit of research into the other MidpointRounding options it seems some of them are not very intuitive, as in they're nothing to do with midpoint logic at all 😕 which probably makes things even worse! see: dotnet/runtime#38160 .

[alfonsogarciacaro]

Closing for now as the solution to this is not trivial. Please reopen if someone wants to work on this.