-----Original Message----- From: boost-bounces@lists.boost.org [mailto:boost-bounces@lists.boost.org] On Behalf Of Gaetano Mendola Sent: Monday, November 26, 2012 1:34 PM To: boost@lists.boost.org Cc: John Maddock Subject: Re: [boost] [math] boost::math::isfinite fails with --fast-math
On 11/26/2012 02:13 PM, John Maddock wrote:
I'm wandering if this is to be expected, the following code fails if compiled with --fast-math:
//==================================================== #include <boost/math/special_functions/fpclassify.hpp> int main() { const float a = 0.0f/0.0f; assert(not boost::math::isfinite(a)); }
Which fails - does the 0/0 actually yield an infinity? Or is it isfinite that fails?
Either way is hard to make guarentees once you enable an option like that.
The following code:
#include <boost/math/special_functions/fpclassify.hpp> int main() { const float a = 0.0f/0.0f; std::cout << "a => " << a << std::endl; std::cout << "boost::math::isfinite(a) => " << boost::math::isfinite(a) << std::endl; std::cout << "a != a: " << (a!=a ? "true" : "false") << std::endl; }
gives:
a => nan boost::math::isfinite(a) => 1 a != a: true
This appears to perhaps not conform to this -ffinite-math-only, <<<<<<<<<<<< so the IEEE pattern for infinity (or NaN?) will never be set. " -ffast-math Sets -fno-math-errno, -funsafe-math-optimizations, -fno-trapping-math, -ffinite-math-only, <<<<<<<<<<<< so the IEEE pattern for infinity will never be set. -fno-rounding-math, -fno-signaling-nans Or does this mean quiet NaNs *are* supported? And do the specific tests boost::math:: isnan and isinf help you any more? (They shouldn't, I think). Can you achieve what you want (-funsafe-math-optimizations for speed ?) by specifying individual options? And provide some test cases and raise a Trac ticket (No promises - the logic is more than byzantine enough already). Paul