[Bug math/16449] S/390 Missing exceptions with llrint

["joseph at codesourcery dot com" <sourceware-bugzilla at sourceware dot org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=16449

--- Comment #4 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
On Tue, 28 Jan 2014, stli at linux dot vnet.ibm.com wrote:

> the cast from float to long long is handled by a call to libgcc __fixsfdi
> function. This function in (libgcc/config/s390/32) does not raise the INVALID
> exception.
> According to c99 standard the cast is a conversion from float to integer and
> "If the value of the integral part cannot be represented by the integer type,
> the behavior is undefined."
> Is it correct to rely on the simple cast in glibc?

Annex F changes this from undefined to unspecified value plus INVALID 
exception (F.4 in C99).

There may well be a case for working around GCC deficiencies in this area 
in glibc (conditional on architecture and GCC version needing it) - such 
problems apply to several architectures, with the details of what needs 
fixing varying from architecture to architecture - but I'd also encourage 
reporting libgcc bugs found, and fixing them if possible.

(Properly supporting Annex F in GCC is a large amount of work - but I'd 
like to see it done, and indeed the more recent under-development C 
bindings for IEEE 754-2008.  This particular issue is one of the bits that 
could be addressed by a reasonably small self-contained patch.)

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