[Bug libquadmath/68686] tgammaq(x) is always negative for noninteger x < 0

[3dw4rd at verizon dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68686

--- Comment #4 from Ed Smith-Rowland <3dw4rd at verizon dot net> ---
Created attachment 41079
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41079&action=edit
Correct sign of negative arg tgammaq.

Basically,

return (x > 0.0Q || (int)(-x) & 1) ? +res : -res;

CL:
2017-03-29  Edward Smith-Rowland  <3dw4rd@verizon.net>

        PR libquadmath/68686
        * math/tgammaq.c: Correct sign for negative argument.
        * testsuite/pr68686.c

We need a testsuite for libquadmath?

pr68686.c
--------------------------------------------------------
#include <quadmath.h>
#include <assert.h>

int
main(void)
{
  __float128 result = tgammaq(-1.5Q);
  assert(result > 0.0Q);

  result = tgammaq(-2.5Q);
  assert(result < 0.0Q);

  return 0;
}
--------------------------------------------------------