Fix bug with ‘mod’ and float+bignum

Problem reported by Andy Moreton in:
https://lists.gnu.org/r/emacs-devel/2018-08/msg00442.html
* src/floatfns.c (fmod_float): Work even if an arg is a bignum.
* test/src/floatfns-tests.el (bignum-mod): New test.

2 files changed, 5 insertions, 4 deletions

diff --git a/src/floatfns.c b/src/floatfns.c
index ea2eb1016b1..713d42694ff 100644
--- a/src/floatfns.c
+++ b/src/floatfns.c
@@ -514,10 +514,8 @@ With optional DIVISOR, truncate ARG/DIVISOR.  */)
 Lisp_Object
 fmod_float (Lisp_Object x, Lisp_Object y)
 {
-  double f1, f2;
-
-  f1 = FLOATP (x) ? XFLOAT_DATA (x) : XFIXNUM (x);
-  f2 = FLOATP (y) ? XFLOAT_DATA (y) : XFIXNUM (y);
+  double f1 = XFLOATINT (x);
+  double f2 = XFLOATINT (y);
 
   f1 = fmod (f1, f2);
 
diff --git a/test/src/floatfns-tests.el b/test/src/floatfns-tests.el
index 7714c05d60a..43a2e278290 100644
--- a/test/src/floatfns-tests.el
+++ b/test/src/floatfns-tests.el
@@ -46,4 +46,7 @@
   (should (= (+ (logb most-positive-fixnum) 1)
              (logb (+ most-positive-fixnum 1)))))
 
+(ert-deftest bignum-mod ()
+  (should (= 0 (mod (1+ most-positive-fixnum) 2.0))))
+
 (provide 'floatfns-tests)