[PATCH] Remove __isinf uses that rely on signed return value

[Joseph Myers]

On Tue, 2 Jun 2015, Szabolcs Nagy wrote:

> On 02/06/15 18:15, Wilco Dijkstra wrote:
> > The printf code contains a few uses of __isinf where the sign is used - replace these with separate
> > isinf and signbit. Also change __isnan into isnan.
> 
> i suspect it slightly changes semantics on x86 (for the better).

It shouldn't.  isnan, the type-generic macro, just calls __isnanf / 
__isnan / __isnanl depending on the type of the argument.

> i386 __isnanl does not seem to handle invalid ld80 representations.
> 
> if exponent != 0 and significand>>63 == 0 then it's a "pseudo normal"
> or "pseudo infinite" value that the fpu would categorize as nan, but
> not __isnanl.
> 
> (passing around long doubles with invalid representation is ub,
> but probably __isnanl should be consistent with fcom instruction
> to be safe when it is used on random bytes).

glibc policy on invalid long double values (both ldbl-96 and I think 
ldbl-128ibm) is bounded undefined behavior (unspecified result, 
unspecified exceptions, no expectation of any consistency, but should 
avoid crashing the program / out-of-bounds stores).

-- 
Joseph S. Myers
joseph@codesourcery.com