80 bit floating point emulation

[JG]

On Friday, 8 July 2022 at 22:04:38 UTC, Walter Bright wrote:
> In order for DMD to become a proper cross compiler, it needs to 
> be able to emulate 80 bit floating point. The full x87 doesn't 
> need to be emulated, just
> add, sub, mul, div, cmp, neg, tst.
>
> [...]

Thinking of spending a few hours later to get an idea of how long 
it will take to do. Any specification to work from?