Re: libm

[Szabolcs Nagy <nsz@port70.net>]

* Rich Felker <dalias@aerifal.cx> [2012-03-05 09:04:59 -0500]:
> On Mon, Mar 05, 2012 at 09:51:35AM +0100, Szabolcs Nagy wrote:
> Hm? If you need a macro to test whether an argument is an integer or
> floating point, try this:
> 
> #define __IS_FP(x) !!((1?1:(x))/2)
> 

oh nice
(and subtle)

> I can do it, but might be another day or two. Feel free to keep fixing
> stuff up in the mean time if you have time. :)
> 

ok

> > i saw that you removed the compound literal definition of
> > NAN, INFINITY etc from math.h
> > 
> 
> The removal has nothing to do with c89; it's actually the fact that
> the compound literal definition was not a constant expression and the
> standard requires these macros to expand to constant expressions.
> 

i see

> adopted it. In any case I see no good way to define them without
> compound literals except the function calls..
> 

btw while testing these macros i noticed that when
multiple classification macros are used fpclassify
gets called many times
(with the previous solution)

the extra calls could be optimized by adding
__attribute__((const)) to fpclassify
(resulted less calls, smaller code size etc)

> > hm but float compare will compile to different instruction
> > so there is at least performance difference
> 
> Yes. In principle it would be faster to do everything as floating
> point so no store/load delays are needed. In relality I doubt it makes
> much of a difference. In almost all of these functions the actual
> computation time dominates.
> 

i see