* lisp/emacs-lisp/cl-extra.el (cl-isqrt): Speed up bignum case

1 files changed, 2 insertions, 3 deletions

diff --git a/lisp/emacs-lisp/cl-extra.el b/lisp/emacs-lisp/cl-extra.el
index 90533295b68..ca33c56a958 100644
--- a/lisp/emacs-lisp/cl-extra.el
+++ b/lisp/emacs-lisp/cl-extra.el
@@ -332,10 +332,9 @@ If so, return the true (non-nil) value returned by PREDICATE.
 
 ;;;###autoload
 (defun cl-isqrt (x)
-  "Return the integer square root of the argument."
+  "Return the integer square root of the (integer) argument."
   (if (and (integerp x) (> x 0))
-      (let ((g (cond ((<= x 100) 10) ((<= x 10000) 100)
-                     ((<= x 1000000) 1000) (t x)))
+      (let ((g (ash 2 (/ (logb x) 2)))
             g2)
         (while (< (setq g2 (/ (+ g (/ x g)) 2)) g)
           (setq g g2))