https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89991
--- Comment #15 from Andrew Pinski <pinskia at gcc dot gnu.org> --- (In reply to Jonathan Wakely from comment #13) > (In reply to Steve Kargl from comment #10) > > % g++8 -o z a.cpp -lm && ./z > > z = (-1.84250315177824e-07,-0) > > pow(z,0.5) = (2.62836076598358e-20,-0.000429243887758258) > > sqrt(z) = (0,0.000429243887758258) > > sqrt(conj(z)) = (0,0.000429243887758258) > > conj(sqrt(z)) = (0,-0.000429243887758258) > > > > This looks wrong. > > I can't reproduce this, I get: > > z = (-1.84250315177824e-07,-0) > pow(z,0.5) = (2.62836076598358e-20,-0.000429243887758258) > sqrt(z) = (0,-0.000429243887758258) > sqrt(conj(z)) = (0,0.000429243887758258) > conj(sqrt(z)) = (0,0.000429243887758258) My bet now comes to the fact there have been improvements to glibc which changed the behavior here .... Also I used the wrong term, it is the branch cut that is the issue. Most of the branch cuts were fixed in glibc in 2012; though there might have been some fixed later on.
