data.cc failing 1 test

[John W. Eaton]

On 16-Dec-2009, Rik wrote:

| 'make check' is failing for one test in data.cc.  I'm pretty sure I was
| able to pass the entire test suite as little as two weeks ago.
| 
| >>>>> processing octave-dev/src/data.cc
|   ***** assert(log2(complex(0,Inf)), Inf + log2(i));
| !!!!! test failed
| assert (log2 (complex (0, Inf)),Inf + log2 (i)) expected
| Inf + 2.266i
| but got
| Inf - NaNi
| NaNs don't match

What compiler are you using?  What options?  For the following
program, I see the following result with g++ -O0,

  $ g++ -O0 cmplx-bug.cc
  $ ./a.out
  inf, (0,inf)
  (inf,nan)

but with -O2, I see

  $ g++ -O2 cmplx-bug.cc
  $ ./a.out
  inf, (0,inf)
  (inf,2.26618)

So I think this is a bug in g++ or the complex class in the GNU
libstdc++ library.

I'm using

  $ g++ -v
  Using built-in specs.
  Target: x86_64-linux-gnu
  Configured with: ../src/configure -v --with-pkgversion='Debian 4.3.4-6' 
--with-bugurl=file:///usr/share/doc/gcc-4.3/README.Bugs 
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared 
--enable-multiarch --enable-linker-build-id --with-system-zlib 
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix 
--enable-nls --with-gxx-include-dir=/usr/include/c++/4.3 --program-suffix=-4.3 
--enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc --enable-mpfr 
--with-tune=generic --enable-checking=release --build=x86_64-linux-gnu 
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
  Thread model: posix
  gcc version 4.3.4 (Debian 4.3.4-6) 

but I also see the same result with g++ 3.3, 4.0, 4.1, and 4.2.

jwe

#include <iostream>
#include <complex>

std::complex<double>
xlog2 (const std::complex<double>& x)
{
#if defined (M_LN2)
  static double ln2 = M_LN2;
#else
  static double ln2 = log (2);
#endif

  return std::log (x) / ln2;
}

int
main (void)
{
  double inf = 1.0 / 0.0;
  std::complex<double> infi (0.0, inf);
  std::cerr << inf << ", " << infi << std::endl;
  std::cerr << xlog2 (infi) << std::endl;
  return 0;
}