Re: The arithmetic support of SCmode and DCmode.

[craig at jcb-sc dot com]

>  In message <19990407030325.22377.qmail@deer>you write:
>  > Does anyone know if there are any systems targeted by egcs/gcc that
>  > would execute the "direct" double-precision version of c_div *slower*
>  > than the current, "slow", safe way, assuming it used single precision?
>Sure.  Systems that don't implement double precision FP ops in hardware, but
>which do implement single precision in hardware.
>
>Or systems that don't implement any floating point in hardware :-)

Is there some kind of target macro a library like libg2c can test to
determine this?  If not, could we add one, perhaps even a ratio
named something like DOUBLE_VERSUS_FLOAT_PERFORMANCE, with 10 being
`==', 20 being twice as slow, 5 being twice as fast (theoretically
possible; 9 or 8 might even happen on some machines today, e.g. Alpha),
as a *rough* guideline?  There might already be a macro that indicates
that `float' runs pretty much as fast as `double', in terms of the
computation operations (excluding load/store), which would be fine
for now if we could get at it in libg2c.

(In my "nearly-ideal" world, we'd be using a language that naturally
included means to express alternate choices for algorithms, so c_div.c
would contain two, perhaps several, versions of the code, and the
compiler would figure out which would likely run fastest on the target
machine....)

        tq vm, (burley)