Subject: Re: [boost] C++11 compilers and fenv
From: John Maddock (jz.maddock_at_[hidden])
Date: 2015-05-06 13:28:40
> How are c++11 boost libraries dealing with these compiler issues?
> I got some options in mind:
> â Implement everything using custom detections, this will work in every compiler, but it will run slower for everyone too.
> â Finding a compiler with the support, implementing the library using the FENV, and assuming compilers will support it when the library is finished and reviewed.
> â Detect somehow the FENV pragma was not processed and have 2 implementations. No idea how to detect something like this.
> Had someone dealt with similar problem already?
> Is there a common approach?
No, but you've had some good suggestions, and I would just add my +1
that FENV is unlikely to be very widely available due to the issues
Some other resources that may help you:
* If you're targeting C++11 then you can reasonably rely on
std::isfinite and friends.
* If as suggested you want to try bit-fiddling to get the status of an
FP value, then that code is already in Boost.Math (see fpclassify.hpp
and includes thereof) and you can steal as required ;-) Obviously any
software solution will be *much* slower than getting the hardware to
raise an exception for you.
* When it comes to testing, libs/multiprecision/test/test_arithmetic.hpp
has a template function "test_arithmetic" that's designed to test every
conceivable arithmetic operator (and permutations thereof).
* In fact it occurs to me that you could implement what you had in mind
in about 10 minutes using Boost.Multiprecision - albeit in a more
heavyweight and less flexible manner than a dedicated solution.... in
fact I've attached sample code below. Given that we known that the
"abstraction overhead" of boost::multiprecision::number with
arithmetic_backend is very small, this might make a quick/easy/dirty way
to test various FP-testing methods?
Here's the test code:
typedef arithmetic_backend<double> fp_wrapper;
typedef logged_adaptor<fp_wrapper> backend_type;
void log_postfix_event(const fp_wrapper& val, const char*
typedef number<backend_type, et_off> checked_double;
int main(int argc, char *argv)
using namespace boost::multiprecision;
checked_double a(2), b(0);
a /= b;
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