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Re: VAX floating point formats & tuning GCC for CPU models (was Re: Some more patches for GCC...)



On Mon, Apr 4, 2016 at 4:16 PM, Paul Koning <paulkoning%comcast.net@localhost> wrote:
> Does -msoft-float work correctly?  I had the impression, perhaps mistaken, that the GCC soft float library uses IEEE format, which of course none of the VAX float formats use.


GCC doesn't support -msoft-float on VAX at all. It's apparently a
target-specific option and some targets support it and some don't.

I would expect -msoft-float if it existed to be entirely IEEE format
and use a different set of libm functions that expect IEEE format. Of
course there are other libc functions that expect float arguments and
that could be an issue too...

If it existed my plan was to try to compile just parts of the system
with -msoft-float and then track down everywhere that floats from that
part could escape into the rest of the code and insert a conversion.
In my case that was going to be tractable because the part I wanted to
compile with -msoft-float was the user-visible datatype and there
should already be a simple conversion macro anywhere those are used
internally anyways. The goal was to guarantee that the internal code
doesn't depend on IEEE floating point.

-- 
greg


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