On 2010-03-17 17:14:37 +0100, Giacomo A. Catenazzi wrote:
> From C standard (not really the standard, but the draft n1256:
> 5.2.4.2.2, point 5):
> 
> : The accuracy of the floating-point operations (+, -, *, /) and of
> : the library functions in <math.h> and <complex.h> that return
> : floating-point results is implementationdefined,
> : as is the accuracy of the conversion between floating-point
> : internal representations and string representations performed by
> : the library functions in <stdio.h>, <stdlib.h>, and <wchar.h>.
> : The implementation may state that the accuracy is unknown.

The values are defined by 5.2.4.2.2p2 (see the equality). The model
is that a floating-point number represents a real number, not an
interval.

"accuracy" is a measure of the difference between the exact value
and the (rounded) value returned by the function.

> So maybe the bug is to define __STDC_IEC_559__ on such case.
> 
> OTOH, section F9.1 don't require (my interpretation)
> trigonometric to be IEC 60559 functions. It has such requirement
> for more elementary functions, e.g. for sqrt (see section F3).

Yes, elementary functions are not covered by Annex F (which is on
the old IEEE 754-1985 standard). However, a C implementation could
claim to conform to IEEE 754 (i.e. more than being conform to
ISO C). This is more a quality of implementation.

Note: I don't know about other languages, whose implementation could
also use the glibc. They could be more restrictive than C.

-- 
Vincent Lefèvre <vinc...@vinc17.net> - Web: <http://www.vinc17.net/>
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Work: CR INRIA - computer arithmetic / Arénaire project (LIP, ENS-Lyon)



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