https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68652
--- Comment #5 from Jean-Claude Arbaut <arbautjc at gmail dot com> --- I posted the bug report here, I hope it's the right place now: http://sourceforge.net/p/mingw-w64/bugs/517/ Nothing yet. However, I had a look at the assembly output, and it's interesting: the Fortran gamma function translates to a call to tgamma. tgamma is a C99 function, which can be found in several places: Apple libm, gcc source, glibc, netbsd... and the mingw-w64 source. Actually, the assembly output also tells me it's a function in tgamma.c that merely calls __tgamma_r. This is in the mingw-w64 source (mingw-w64-v4.0.4\mingw-w64-crt\math\tgamma.c and tgammaf.c). I tried a C program, and it shows the same bug, with some variations, with mingw-w64 4.9.3 and 5.2.0 (the recent rev1), and also with Rtools (mingw-w64 4.6.3), the toolchain for the statistical package R. Similar program for tgammaf: #include <stdio.h> #include <math.h> int main() { double x, y; for(;;) { scanf("%lf", &x); y = tgamma(x); printf("%.4e %.4e\n", x, y); } return 0; } All in all: * 32 bits GCC tgamma returns NaN for integer x >= 710 (the program prints -1.#INDe+000), but it's even worse than that: for 710.5 for instance, I get zero (also for 2000.5, 2100.5, and probably many other values of x). tgammaf does *not* fail for large values, and it returns Inf. However, it gets slower and slower for large values. * 64 bits gcc same problem with tgamma, though I don't get zeros. tgammaf hangs for integer x >= 1677720 (either I was off by 1 in my preceding post, or it's a slightly different version of mingw-w64, I'm not sure since it wasn't on the same machine). Just a note about the tgamma implementation of mingw-w64: it seems to use some code from Cephes (a library by Stephen Moshier, see www.moshier.net), but apparently only functions to evaluate polynomials. I'll have to investigate further what really goes wrong in tgamma.c and tgammaf.c. There is also a tgammal.c that is probably buggy as well.
