(compare-windows): Use compare-buffer-substrings.

1 files changed, 6 insertions, 9 deletions

diff --git a/lisp/compare-w.el b/lisp/compare-w.el
index 13b7d4d1794..d4d6a4d746e 100644
--- a/lisp/compare-w.el
+++ b/lisp/compare-w.el
@@ -106,24 +106,21 @@ If `compare-ignore-case' is non-nil, changes in case are also ignored."
       ;; Try advancing comparing 1000 chars at a time.
       ;; When that fails, go 500 chars at a time, and so on.
       (let ((size 1000)
-            success-1)
+            success-1
+            (case-fold-search compare-ignore-case))
         (while (> size 0)
           (setq success-1 t)
+          ;; Try comparing SIZE chars at a time, repeatedly, till that fails.
           (while success-1
             (setq size (min size (- maxp1 p1) (- maxp2 p2)))
-            (save-excursion
-              (set-buffer b2)
-              (setq s2 (buffer-substring p2 (+ size p2))))
             (setq success-1
                   (and (> size 0)
-                       (if compare-ignore-case
-                           (let ((case-fold-search t))
-                             (save-excursion
-                               (search-forward s2 (+ p1 size) t)))
-                         (equal (buffer-substring p1 (+ size p1)) s2))))
+                       (= 0 (compare-buffer-substrings b2 p2 (+ size p2)
+                                                       b1 p1 (+ size p1)))))
             (if success-1
                 (setq p1 (+ p1 size) p2 (+ p2 size)
                       success t)))
+          ;; If SIZE chars don't match, try fewer.
           (setq size (/ size 2)))))
 
     (goto-char p1)