Re: pbulk bootstrap: `awk` running into FP overflow during bison build (Grater picture: How to bootstrap pkgsrc / pbulk?)

["Maciej W. Rozycki" <macro%orcam.me.uk@localhost>]

On Mon, 7 Aug 2023, Anders Magnusson wrote:

> >   Though, hmm, it has struck me that the program might expect the IEEE 754
> > exponent range of the double FP type, which raises a question: which of
> > D_floating and G_floating format has our port chosen?  If it's G_floating,
> > then I'd expect the very narrow difference from IEEE 754 double highly
> > unlikely to hit, however with D_floating where the width of the exponent
> > is the same as with F_floating, i.e. the single FP type, it's actually
> > very likely.
> The vax port uses FD floats.

 I have thought so, but wanted to double-check.

> >   Overall I think we ought to support both, but it might be a bit tricky on
> > the toolchain side, as it's an ABI issue to sort out.  Did any machine
> > actually implement H_floating in hardware, or was it only ever emulated?
> The 780 had H-float in hardware.  Actually, it had all instructions in
> hardware (microcode).

 Do we actually support or intend to support that model?  If not, then I 
would yet need to verify if that's actually legal by the ISO C language 
standard (which I reckon has certain requirements as to the ranges of the 
real data types defined), but I think it would be a reasonable idea to map 
F_floating, D_floating and G_floating quantities respectively to the 
`float', `double' and `long double' data types.

 This might not immediately help the case at hand, but would lay grounds 
for the ABI (think C++ symbol name mangling), and then with a clever 
arrangement we might be able to make most things designed with IEEE 754 in 
mind work as expected.  I.e. we could have a compilation flag that makes 
the `double' and `long double' data types both map to G_floating, but 
encoded as `long double' at the ABI level, so that interlinking with code 
that uses the D_floating data type works.  I think it can be made seamless 
as hardware supports the four FP data types all at once without the need 
to switch modes or suchlike.

 Note that all the three narrower hardware FP data types are already 
supported by GCC, unlike H_floating.

  Maciej