http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48602
--- Comment #25 from Thomas Henlich <thenlich at users dot sourceforge.net> 2011-04-18 08:39:17 UTC --- After some testing, I found the problem to be optimization-related. It seems the following term is calculated as a long double and not rounded before the "if (m < temp)" comparison, resulting in an unexpected and in this case invalid result. temp = calculate_exp(mid - 1) * (1 - r * rexp_d); Compare: $ gcc -O2 write_float.c && ./a.out d=2 $ gcc -O2 -fexcess-precision=standard write_float.c && ./a.out d=1
