configure and asinl function problem

Tim Prince tprince@myrealbox.com
Sat Oct 8 20:12:00 GMT 2005


Joost Kraaijeveld wrote:
> On Sat, 2005-10-08 at 07:50 -0700, Tim Prince wrote:
> 
>>such as the one used in the libstdc++ build itself.  Maybe we should 
>>look into how libstdc++ decides it can support asinl() on Cygwin.  Did 
> 
> Actually asinl is a built-in functions provided by GCC, so I
> *think/hope* that it just is a matter of adding those functions to a
> header? 
> 
> See:
> http://gcc.gnu.org/onlinedocs/gcc-3.4.4/gcc/Other-Builtins.html
> 
I've never seen trig functions "provided" by gcc; a very few math 
built-ins are implemented for i386 (fabs, sqrt, et al., where it is 
clear what needs to be done to support the various -march= options). gcc 
has always followed the tradition of relying on someone else to provide 
the C math library, and the corresponding headers.
To me, at least, the provision of a framework for defining built-in 
functions is a separate question from actually "providing" them, in a 
form ready to use.
Commonly used linux glibc headers tend to over-ride even the existing 
limited built-in implementation, so gcc configure has to deal with that. 
  cygwin continues to get math functions from newlib, which supports 
primarily platforms without long double.
I checked libstdc++ config.log, and it does determine that cygwin 
supports no long double trig functions.  As a result, libstdc++ is built 
  with _asinl() calling asin().  It would seem that a configure script 
which comes to a different conclusion about cygwin math libraries than 
the ones used by gcc must be broken.


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