Fix (round FLOAT BIGNUM) bug

* src/floatfns.c (rounding_driver): Fix bug when one
argument is a float and the other is a bignum.
* test/src/floatfns-tests.el (bignum-round): Test for the bug.

2 files changed, 10 insertions, 2 deletions

diff --git a/src/floatfns.c b/src/floatfns.c
index 2f33b8652b2..13ab7b0359f 100644
--- a/src/floatfns.c
+++ b/src/floatfns.c
@@ -355,6 +355,8 @@ rounding_driver (Lisp_Object arg, Lisp_Object divisor,
       CHECK_NUMBER (divisor);
       if (!FLOATP (arg) && !FLOATP (divisor))
         {
+          /* Divide as integers.  Converting to double might lose
+             info, even for fixnums; also see the FIXME below.  */
           if (EQ (divisor, make_fixnum (0)))
             xsignal0 (Qarith_error);
           int_divide (mpz[0],
@@ -363,10 +365,11 @@ rounding_driver (Lisp_Object arg, Lisp_Object divisor,
           return make_integer_mpz ();
         }
 
-      double f1 = FLOATP (arg) ? XFLOAT_DATA (arg) : XFIXNUM (arg);
-      double f2 = FLOATP (divisor) ? XFLOAT_DATA (divisor) : XFIXNUM (divisor);
+      double f1 = XFLOATINT (arg);
+      double f2 = XFLOATINT (divisor);
       if (! IEEE_FLOATING_POINT && f2 == 0)
         xsignal0 (Qarith_error);
+      /* FIXME: This division rounds, so the result is double-rounded.  */
       d = f1 / f2;
     }
 
diff --git a/test/src/floatfns-tests.el b/test/src/floatfns-tests.el
index d41b08f7965..9a382058b43 100644
--- a/test/src/floatfns-tests.el
+++ b/test/src/floatfns-tests.el
@@ -70,6 +70,11 @@
       (should (= n (floor n)))
       (should (= n (round n)))
       (should (= n (truncate n)))
+      (let ((-n (- n))
+            (f (float n))
+            (-f (- (float n))))
+        (should (= 1 (round n f) (round -n -f) (round f n) (round -f -n)))
+        (should (= -1 (round -n f) (round n -f) (round f -n) (round -f n))))
       (dolist (d ns)
         (let ((q (/ n d))
               (r (% n d))