Draft C bindings for IEEE 754-2008 part 4 now available

[Joseph S. Myers]

On Tue, 7 Jan 2014, Florian Weimer wrote:

> On 01/04/2014 07:21 PM, Joseph S. Myers wrote:
> 
> > FYI: a draft set of C bindings for additional floating-point functions
> > from IEEE 754-2008 are now available (draft TS 18661-4):
> 
> Is there an accurate summary of IEEE 754-2008 available online?

No.  It's available for purchase from IEEE, or through IEEE Xplore if you 
have a site subscription to that.  (ISO/IEC/IEEE 60559:2011 is just IEEE 
754-2008 with different cover pages / front matter.)

> I'm asking because IEEE 754 is widely quoted, but nobody really seems to know
> what's in it.  (It seems that some operations are allowed to be off by an ulp
> or more, for instance, which I find rather surprising.)

The IEEE 754 operations are corrected rounded.  However, the C bindings 
choose to provide most of the recommended operations from IEEE 754-2008 
subclause 9.2 only in versions with unspecified accuracy, and not in 
correctly rounded versions, with names being reserved for the correctly 
rounded versions but no requirement that those functions be provided.  (As 
far as I know, the state of the art on exhaustive searches for worst cases 
for correct rounding - as needed to implement correctly rounded 
transcendental functions with bounded resource use - does not make such 
searches feasible for IEEE binary128, which is a clear reason not to 
require such functions to be provided.)

-- 
Joseph S. Myers
joseph@codesourcery.com