Re: [Bug-gsl] Bug in sys/ldfrexp.c

[Andrew W. Steiner]

I'm surprised about the presence of 1e308 in the isfinite macro. Do we
have to worry about that being somewhat machine dependent?

On 10/27/07, Chris Mihelich <address@hidden> wrote:
> Good evening,
>
> I wish to report and correct the following bugs in sys/ldfrexp.c:
>
> (1) gsl_ldexp computes a power of 2 (p2) that may overflow or
> underflow even though the correct answer is representable;
> consequently the return value x * p2 may be spuriously zero or
> infinity.
>
> (2) gsl_frexp can hang (this is what bit me in the rear at work
> yesterday) if its call to gsl_ldexp spuriously returns zero or
> infinity as in (1).  The first while loop divides infinity by 2.0 over
> and over and wonders why it doesn't get any smaller; the second while
> loop has an analogous problem with zero.
>
> I have attached a tgz ball containing revised copies of the following
> files hoping that you will correct these faults in the next release:
>
> (a) sys/ldfrexp.c, rewritten from scratch.  You will want to put
> suitable identifying comments at the top.
> (b) sys/test.c, to which I have added very thorough tests for
> gsl_ldexp and gsl_frexp.
> (c) test/results.c, to which I have added a function
> gsl_test_rel_subnormals_ok that is just like gsl_test_rel except for
> not automatically failing if an argument is subnormal.  The additions
> in (b) need this.
> (d) err/gsl_test.h, to which I have added the declaration of
> gsl_test_rel_subnormals_ok.
>
> Thank you for continuing to maintain GSL.  Aside from this cute little
> glitch, it has been a very helpful tool for me in my day job.
>
> Chris Mihelich (address@hidden, 609-658-5827)
> "Never made it as a wise man"
>
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