Re: [Mingw-users] expm1()

[Greg C. <chi...@co...>]

On 2005-01-29 00:41 AM, Danny Smith wrote:

> Greg Chicares wrote:
> 
>>On 2005-01-27 03:29 AM, Danny Smith wrote:
>>
>>>Greg Chicares wrote:
>>
>>I will. First, though, let's try to solve the M_LN2 problem.
>>I'd hate to hardcode a constant value in expm1() now, when what
>>we really want is to use that macro, but with a value that's
>>not overstated.
> 
> On second thought, hardcoded values of the constants may be the way to go,
> particulary if we put inline versions of the functions in math.h.  The M_*
> defines are !__STRICT_ANSI__, so we can't be sure that they will be visible (eg,
> if --std=c99).

Good point. I've updated
http://sourceforge.net/tracker/index.php?func=detail&aid=1109674&group_id=2435&atid=302435
and I believe it reflects all our discussions to date.

Please take a look at the included test program. It shows
differences of exactly one between expm1() and exp()-1 for
arguments extreme enough to return infinity or indefinite.

C99 7.12.6.3/2 says
   "A range error occurs if x is too large."
but 7.12.1/3 doesn't seem to say what an implementation
should do when a range error occurs, so I guess anything
goes for extremely high arguments.

I'm not sure what should happen for an argument of -INF.
I get an indefinite for both expm1(-INF) and exp(-INF)-1.
7.12.1/5 seems to allow that if we regard indefinites as
representable "without extraordinary roundoff error".