FE_INEXACT exception question (lrint function on aarch64)

[Joseph Myers]

On Wed, 21 Jun 2017, Steve Ellcey wrote:

> I have a question about floating point exceptions and the lrint function.
> While working on ILP32 mode for aarch64 I get these glibc failures in 32 bit
> mode (but not in 64 bit mode).  I believe that all of these cases are
> due to aarch64 setting the FE_INEXACT exception as well as the FE_INVALID
> exception whereas the x86 sets only the FE_INVALID exception.  If we
> were converting to a 64 bit long all of these would raise only the FE_INEXACT
> exception on both the x86 and aarch64 because the resulting values fit into
> a 64 bit long.
> 
> My question is: Is it wrong to set the FE_INEXACT exception as long as
> one is also setting the FE_INVALID exception?  If so, what standard
> (C,C++,POSIX,IEEE) requires that we not set it.

See C11 F.10.6.5, "When they raise no other floating-point exception and 
the result differs from the argument" as the condition for raising 
inexact.  As a fully specified function bound to IEEE 754 operations, 
there should be no spurious "inexact".

-- 
Joseph S. Myers
joseph@codesourcery.com