[PATCH, PR] Crash of Bessel functions at x==0!

[Ed Smith-Rowland]

On 02/07/2013 06:45 AM, Paolo Carlini wrote:
> Hi,
>
> On 02/07/2013 04:34 AM, Ed Smith-Rowland wrote:
>> All,
>>
>> This patch catches cyl_bessel_i, and cyl_bessel_j returning -nan for 
>> zero argument.  Not sure how i missed that.
>>
>> Anyhow, this patch cleans that up.
>> Also, spurious const is removed from numeric arguments of internal 
>> functions throughout the TR1 special maths.
> These two hunks look straightforward and can certainly go in now. Thanks.
>> Also, a better asymptotic treatment of Bessel functions is supplied.
> This one worries me a bit: we don't want to introduce regressions on 
> some less known platform at this stage. Can we delay it to post 4.8.0? 
> 4.8.1 would be also fine. 
I get it.  I'll split this off.  I'd like a unit test on this myself.
> By the way, in general, in __cyl_bessel_jn_asymp and in other places, 
> something like an hardcoded 1000, without a comment, without a 
> specific analysis explaing why 1000 instead of 100 or 10000 is 
> something we should really, really, really, avoid. At minimum, if we 
> can't do better in terms of analyzing the behavior of each specific 
> algorithm, those constants should be given a name (likely bundled 
> together in sets), be documented in the docs to enable the users to 
> change the values away from the defaults.
>
I agree.  The math special functions are going to get a working on these 
and other issues.  Then my goal is to proceed, for 4.9 of course, with 
ISO/IEC 29123 - basically adding these functions to namespace std, 
versioned, and guarded with a macro as described 
inhttp://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3060.pdf.
<http://www.open-std.org/jtc1/sc22/wg21/docs/projects#29123>
> In any case, please remove the "// { dg-do compile }" from the 
> testcase: we want to *run* it (the default behavior), right? Also, 
> please try to follow the common format, have a separate function with 
> the tests, called by main, definining a test variable, etc, etc.
>
> Thanks!
> Paolo.
>
>