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Re: RFC: Define __FPMATH_387__ and __FPMATH_SSE__

On Thu, Mar 02, 2006 at 04:44:50PM +0100, Jakub Jelinek wrote:
> On Thu, Mar 02, 2006 at 07:38:47AM -0800, H. J. Lu wrote:
> > Yes. That is for float and double functions in libm.
> > 
> > > to touch x387
> > > flags for XFmode long long operations.
> > 
> > I assume you meant long double. If the library knows it doesn't long
> > double, it doesn't need to touch x87 unit control.
> But if you call one of the standard fenv.h functions, they
> are supposed to affect not just the calling routine (where you
> could through preprocessor magic tell what it uses, though e.g.
> not for inline asm), but for the whole process.  And I don't understand
> how you can prove that if you call fesetround or similar from
> -mfpmath=sse compiled source file that the program doesn't anywhere
> in some other library or in the main binary use x87 unit (or vice versa).

I was talking about glibc. sysdeps/ieee754/flt-32/e_expf.c has

      feholdexcept (&oldenv);
      fesetround (FE_TONEAREST);


      /* Return result.  */
      fesetenv (&oldenv);

I don't see why it has to touch x87 unit. The same applies to most,
if not all, float/double functions in glibc.


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