math::signbit fails to report -0

[tegtmeye@…]

math::signbit fails to report -0. Observed from boost::units, IEEE 754 handling

#include <boost/math/special_functions/sign.hpp>

#include <iostream>
#include <math.h>

int main(void)
{
  float i=copysign(0.,-1.);
  float j=boost::math::copysign(0.,-1.);
  
  std::cout << "i: " << i << ", signbit: " << std::signbit(i) << "\n";
  std::cout << "j: " << j << ", signbit: " << boost::math::signbit(j) << "\n";

  return 0;
}

[tegtmeye@…]

Sorry, reports on my machine [Mac 10.5, gcc version 4.0.1 (Apple Inc. build 5490)]

i: -0, signbit: 1
j: -0, signbit: 0

[John Maddock]

I believe this has already been fixed in Trunk - unfortunately it didn't make the last release - should make the next one though.

I'm closing this for now, but please reopen if the version of sign.hpp here: ​https://svn.boost.org/trac/boost/browser/trunk/boost/math/special_functions/sign.hpp doesn't fix the issue.