fenv.h implementation questions

[Steven G. Kargl]

Bruce Evans wrote:
> On Sun, 21 Dec 2003, Steven G. Kargl wrote:
> 
> > Is the following a sufficient implementation of fenv.h?
> > _fenv_t and _fexcept_t would be defined in machine/fenv.h,
> > which I haven't implemented, yet.  I'm assuming that
> > these may be architecture specific (e.g., endianness).
> 
> fenv_t and fexcept_t are very MD, and hopefully aren't needed
> in more than 1 file, so they should be declared directly in
> <machine/fenv.h>.

Certainly, fenv_t and fexcept_t are MD, but I don't
believe that their use is restricted to 1 file (unless
I'm totally misinterpreting what you wrote).  Consider,

#include <errno.h>
#include <fenv.h>
#include <math.h>

int foo(x) {
   double x;
   fexcept_t bar;
   errno = 0;
   x = ceil(x);
   if (errno != 0) { /* FE occurred */
      fegetexception(&bar, FE_ALL_EXCEPT);
      /* Do something to address FE */
   } else {
     ....
   }
}

(snip)

> > #ifdef _EXCEPTIONS
> > #define FE_DIVBYZERO	0x00000001	/* Divide by zero */
> > #define FE_INEXACT	0x00000002	/* Inexact flag raised */
> > #define FE_INVALID	0x00000004	/* Invalid operation */
> > #define FE_OVERFLOW	0x00000008	/* Overflow */
> > #define FE_UNDERFLOW	0x00000010	/* Underflow */
> > #define FE_ALL_EXCEPT	0x0000001F	/* Bitwise-or of above flags */
> > #endif /* _EXCEPTIONS */
> >
> > #ifdef _ROUNDING_MODES
> > #define FE_DOWNWARD	0x00000020	/* Round downward */
> > #define FE_TONEAREST	0x00000040	/* Round to nearest */
> > #define FE_TOWARDZERO	0x00000080	/* Round towards zero */
> > #define FE_UPWARD	0x00000100	/* Round upwards */
> > #endif /* _ROUNDING_MODES */
> 
> These should probably all be MD.  It saves a negative amount of code to
> use a common definition since larger code would be required to convert
> between the MI bits and the MI bits.
> 

I'll have to look at SuSv3 again, but the above definitions
should be suitable for both big and little endian machines.
I'm not sure about 32 bit versus 64 bit machines.  Are you
concerned that an architecture may only support a subset of
the above flags?

-- 
Steve
http://troutmask.apl.washington.edu/~kargl/