(isnan): Define even if LISP_FLOAT_TYPE is not defined, since fmod

might need it.
(fmod): Ensure that the magnitude of the result does not exceed that
of the divisor, and that the sign of the result does not disagree with
that of the dividend.  This does not yield a
particularly accurate result, but at least it will be in the
range promised by fmod.

1 files changed, 15 insertions, 3 deletions

diff --git a/src/data.c b/src/data.c
index 6fac1131eba..96d0a1032e7 100644
--- a/src/data.c
+++ b/src/data.c
@@ -2007,11 +2007,11 @@ arith_driver (code, nargs, args)
   return val;
 }
 
-#ifdef LISP_FLOAT_TYPE
-
 #undef isnan
 #define isnan(x) ((x) != (x))
 
+#ifdef LISP_FLOAT_TYPE
+
 Lisp_Object
 float_arith_driver (accum, argnum, code, nargs, args)
      double accum;
@@ -2141,9 +2141,21 @@ double
 fmod (f1, f2)
      double f1, f2;
 {
+  double r = f1;
+
   if (f2 < 0.0)
     f2 = -f2;
-  return (f1 - f2 * floor (f1/f2));
+
+  /* If the magnitude of the result exceeds that of the divisor, or
+     the sign of the result does not agree with that of the dividend,
+     iterate with the reduced value.  This does not yield a
+     particularly accurate result, but at least it will be in the
+     range promised by fmod.  */
+  do
+    r -= f2 * floor (r / f2);
+  while (f2 <= (r < 0 ? -r : r) || ((r < 0) != (f1 < 0) && ! isnan (r)));
+
+  return r;
 }
 #endif /* ! HAVE_FMOD */