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Subject:	gcc-3.4.4-1: c++: cmath: calling std::isnan results in endless loop
From:	Thomas Sailer <sailer AT sailer DOT dynip DOT lugs DOT ch>
To:	cygwin AT cygwin DOT com
Date:	Mon, 27 Feb 2006 15:40:17 +0100
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When I try to call std::isnan(double) from a program compiled with g++
3.4.4, the program gets into an endless loop.

The problem is that gcc compiles
__gnu_cxx::isnan<double>(double) as a tail call to
__gnu_cxx::__capture_isnan<double>(double), and it compiles
__gnu_cxx::__capture_isnan<double>(double) to
__gnu_cxx::isnan<double>(double). It looks to me that this wrapping hack
(that is also in current glibc) only works if isnan is a macro. But on
cygwin, this isn't the case.

I'm using the patch below to work around this problem, but I'm not C++
language lawyer enough to know whether this fulfills all applicable
namespace purity standards...

Tom


--- cmath.orig	2006-02-27 15:15:05.101562500 +0100
+++ cmath	2006-02-27 15:18:51.882812500 +0100
@@ -455,10 +455,16 @@
     int
     __capture_isinf(_Tp __f) { return isinf(__f); }
 
+  using ::isnan;
+  using ::isnanf;
+
   template<typename _Tp>
     int
     __capture_isnan(_Tp __f) { return isnan(__f); }
 
+  template<> int __capture_isnan<double>(double __f) { return ::isnan(__f); }
+  template<> int __capture_isnan<float>(float __f) { return ::isnanf(__f); }
+
   template<typename _Tp>
     int
     __capture_isnormal(_Tp __f) { return isnormal(__f); }



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