(Fexpt): Use floats for negative exponent.

src/ChangeLog

+2005-08-06  Thien-Thi Nguyen  <ttn@gnu.org>
+
+	* floatfns.c (Fexpt): Use floats for negative
+	exponent (computing a root).  Reported by D Goel.
+
 2005-08-02  Richard M. Stallman  <rms@gnu.org>
 	* frame.c (Fframe_char_width): Doc fix.

src/floatfns.c

@@ -460,7 +460,8 @@ DEFUN ("expt", Fexpt, Sexpt, 2, 2, 0,
   CHECK_NUMBER_OR_FLOAT (arg1);
   CHECK_NUMBER_OR_FLOAT (arg2);
   if (INTEGERP (arg1)     /* common lisp spec */
-      && INTEGERP (arg2)) /* don't promote, if both are ints */
+      && INTEGERP (arg2)   /* don't promote, if both are ints, and */
+      && 0 <= XINT (arg2)) /* we are not computing the -ARG2 root */
     {				/* this can be improved by pre-calculating */
       EMACS_INT acc, x, y;	/* some binary powers of x then accumulating */
       Lisp_Object val;