Don’t signal overflow for (expt 1 bignum)

Similarly for (expt 0 bignum) and (expt -1 bignum).
The result is always a -1, 0 or 1, so do not signal overflow.
* src/data.c (expt_integer): Do not signal an overflow if
-1 <= X <= 1.  Be clearer about when overflow is signaled.
* test/src/floatfns-tests.el (bignum-expt): Test this.

1 files changed, 5 insertions, 0 deletions

diff --git a/test/src/floatfns-tests.el b/test/src/floatfns-tests.el
index 643866f1146..62201a877d0 100644
--- a/test/src/floatfns-tests.el
+++ b/test/src/floatfns-tests.el
@@ -51,7 +51,12 @@
 (ert-deftest bignum-expt ()
   (dolist (n (list most-positive-fixnum (1+ most-positive-fixnum)
                    most-negative-fixnum (1- most-negative-fixnum)
+                   (* 5 most-negative-fixnum)
+                   (* 5 (1+ most-positive-fixnum))
                    -2 -1 0 1 2))
+    (should (or (<= n 0) (= (expt 0 n) 0)))
+    (should (= (expt 1 n) 1))
+    (should (or (< n 0) (= (expt -1 n) (if (zerop (logand n 1)) 1 -1))))
     (should (= (expt n 0) 1))
     (should (= (expt n 1) n))
     (should (= (expt n 2) (* n n)))