------- Comment #5 from dominiq at lps dot ens dot fr 2009-06-16 20:30 ------- I have forgotten this one!
> This is not darwin-specific, I also see it happening on x86_64-linux. > > And what's more, the output changes between -m32 and -m64. This is probably related to the extra precision for some floating-point computations (disabled by default on darwin and I refuse to learn what to do to change it!-). > The code is invalid Fortran, so gfortran is not required to give > any sensible output. You know that it is not relevant for this pr!-( would the following make you happier?) integer(8), parameter :: l = z'5fe6eb3be0000000' integer, parameter :: ni = 3 integer :: i, j, n integer(8) :: k real(8) :: a, b, e, m, s !equivalence (b, k) a = 1.0d0 e = epsilon(1.0)/2.0d0**4 m = 0.0d0 s = 0.0d0 n = 0 do n = n + 1 b = a k = transfer(b,k) k = l - ishft(k, -1_8) b = transfer(k,b) do i = 1, ni b = b*(1.5-(0.5*a)*b*b) end do b = b + b*(0.5-(0.5*a)*b*b) ! b = 1.0d0/sqrt(a) m = max(m, abs(a*b*b - 1.0d0)) s = s + abs(a*b*b - 1.0d0) a = a + e if (a == 2.0d0) exit end do print *, n, m/epsilon(a), s/(n*epsilon(a)) end The timings are: [ibook-dhum] f90/bug% gfc -O3 pr36241_db.f90 [ibook-dhum] f90/bug% time a.out 134217728 2.0000000000000000 0.36966567113995552 7.832u 0.010s 0:07.85 99.8% 0+0k 0+0io 0pf+0w [ibook-dhum] f90/bug% gfc -m64 -O3 pr36241_db.f90 [ibook-dhum] f90/bug% time a.out 134217728 2.0000000000000000 0.36966567113995552 3.327u 0.011s 0:03.35 99.4% 0+0k 0+0io 0pf+0w -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36241