Add bignum support to expt

Problem and initial solution reported by Andy Moreton in:
https://lists.gnu.org/r/emacs-devel/2018-08/msg00503.html
* doc/lispref/numbers.texi (Math Functions): expt integer
overflow no longer causes truncation; it now signals an error
since bignum overflow is a big deal.
* src/floatfns.c (Fexpt): Support bignum arguments.
* test/src/floatfns-tests.el (bignum-expt): New test.

1 files changed, 9 insertions, 0 deletions

diff --git a/test/src/floatfns-tests.el b/test/src/floatfns-tests.el
index 43a2e278290..e4caaa1e49b 100644
--- a/test/src/floatfns-tests.el
+++ b/test/src/floatfns-tests.el
@@ -42,6 +42,15 @@
   (should (= most-positive-fixnum
              (- (abs most-negative-fixnum) 1))))
 
+(ert-deftest bignum-expt ()
+  (dolist (n (list most-positive-fixnum (1+ most-positive-fixnum)
+                   most-negative-fixnum (1- most-negative-fixnum)
+                   -2 -1 0 1 2))
+    (should (= (expt n 0) 1))
+    (should (= (expt n 1) n))
+    (should (= (expt n 2) (* n n)))
+    (should (= (expt n 3) (* n n n)))))
+
 (ert-deftest bignum-logb ()
   (should (= (+ (logb most-positive-fixnum) 1)
              (logb (+ most-positive-fixnum 1)))))