------- Comment #9 from sylvain dot pion at sophia dot inria dot fr 2008-12-09 20:03 ------- Incidentally, I submitted to WG21 a few days ago a proposal which will appear in the coming mid-term mailing as N2811, named "Directed Rounding Arithmetic Operations". In the meantime, you can find it here: http://www-sop.inria.fr/members/Sylvain.Pion/cxx/rounded_operations_N2811.pdf
This document proposes the addition of functions like: -------------------------------------------------------------- template < float_round_style r, FloatingPointLike T, FloatingPointLike U > requires True<(r != round_indeterminate)> constexpr auto add(T t, U u) -> decltype(t + u); Returns: The addition of t and u rounded according to r. -------------------------------------------------------------- (and similarly for sub, mul, div, sqrt, fma, and int<->float and float<->float conversions). With these, it would be possible to explictly attach a rounding mode to an operation in the source code. Moreover, their constexpr nature would mean that they would work for compile-time constants as well. This would require a bit of help from the compiler. That would mean that code which cares about rounding modes would have a way to say so, and then, other codes can more easily be dealt with (that is: no need to bother thinking about the effect of -frounding-math on compile-time constants computations). (comments on the proposal are welcome, BTW) -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36912
