fenv.h fixes for softfloat

David Schultz das at freebsd.org
Mon Jan 16 02:26:50 UTC 2012


On Sat, Jan 14, 2012, Ian Lepore wrote:
> With the original value 1.1 instead of 1.0, rint() itself raises
> FE_INVALID, in the path that falls out the bottom.  I added printfs:
> 
>         printf("rint 7a: except %#x\n", fetestexcept(FE_ALL_EXCEPT));
>         INSERT_WORDS(x,i0,i1);
>         printf("rint 7b: except %#x\n", fetestexcept(FE_ALL_EXCEPT));
>         STRICT_ASSIGN(double,w,TWO52[sx]+x);
>         printf("rint 7c: except %#x\n", fetestexcept(FE_ALL_EXCEPT));
>         result = w-TWO52[sx];
>         printf("rint 8: except %#x i0=%#x i1=%#x x=%g w=%g result=%g\n", fetestexcept(FE_ALL_EXCEPT), i0, i1, x, w, result);
>         return result;
> 
> And a run using rint(1.1) gave this output:
> 
>         rint 7a: except 0
>         rint 7b: except 0
>         rint 7c: except 0x10
>         rint 8: except 0x10 i0=0x3ff20000 i1=0x9999999a x=1.125 w=4.5036e+15 result=1

I believe 0x10 is FE_INEXACT on arm, not FE_INVALID.  FE_INEXACT
is correct here, because w+TWO52[sx] is inexact.  That still
doesn't explain the lrint() failures, but it makes them less
mysterious.  For instance, the implementation of the cast from
double to int could raise a bogus inexact exception when the
number is an integer to begin with.  In practice, I think the
emulated casts don't raise the proper exceptions even when they
should.  It might depend on whether it's linking against libgcc's
__fixdfsi() or libc's.

Nice catch with the _fpmath.h bug, by the way.  I'll commit that
fix as well.


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