Do not allow out-of-range character position in Fcompare_strings.

* src/fns.c (validate_subarray): Add prototype.
(Fcompare_substring): Use validate_subarray to check ranges.
Adjust comment to mention that the semantics was changed.  Also see
http://lists.gnu.org/archive/html/emacs-devel/2014-06/msg00447.html.
* lisp/files.el (dir-locals-find-file, file-relative-name):
* lisp/info.el (Info-complete-menu-item):
* lisp/minibuffer.el (completion-table-subvert): Prefer string-prefix-p
to compare-strings to avoid out-of-range errors.
* lisp/subr.el (string-prefix-p): Adjust to match strict range
checking in compare-strings.
* test/automated/fns-tests.el (fns-tests-compare-string): New test.

2 files changed, 31 insertions, 42 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 9f676a6518d..fc47fbc8978 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,11 @@
+2014-06-25  Dmitry Antipov  <dmantipov@yandex.ru>
+
+        Do not allow out-of-range character position in Fcompare_strings.
+        * fns.c (validate_subarray): Add prototype.
+        (Fcompare_substring): Use validate_subarray to check ranges.
+        Adjust comment to mention that the semantics was changed.  Also see
+        http://lists.gnu.org/archive/html/emacs-devel/2014-06/msg00447.html.
+
 2014-06-24  Paul Eggert  <eggert@cs.ucla.edu>
 
         Be more consistent about the 'Qfoo' naming convention.
diff --git a/src/fns.c b/src/fns.c
index 5074ae3b41b..85e9f482fc1 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -50,7 +50,9 @@ static Lisp_Object Qcodeset, Qdays, Qmonths, Qpaper;
 static Lisp_Object Qmd5, Qsha1, Qsha224, Qsha256, Qsha384, Qsha512;
 
 static bool internal_equal (Lisp_Object, Lisp_Object, int, bool, Lisp_Object);
-
+static void validate_subarray (Lisp_Object, Lisp_Object, Lisp_Object,
+                               ptrdiff_t, EMACS_INT *, EMACS_INT *);
+
 DEFUN ("identity", Fidentity, Sidentity, 1, 1, 0,
        doc: /* Return the argument unchanged.  */)
   (Lisp_Object arg)
@@ -232,6 +234,7 @@ string STR1, compare the part between START1 (inclusive) and END1
 \(exclusive).  If START1 is nil, it defaults to 0, the beginning of
 the string; if END1 is nil, it defaults to the length of the string.
 Likewise, in string STR2, compare the part between START2 and END2.
+Like in `substring', negative values are counted from the end.
 
 The strings are compared by the numeric values of their characters.
 For instance, STR1 is "less than" STR2 if its first differing
@@ -244,43 +247,25 @@ If string STR1 is less, the value is a negative number N;
   - 1 - N is the number of characters that match at the beginning.
 If string STR1 is greater, the value is a positive number N;
   N - 1 is the number of characters that match at the beginning.  */)
-  (Lisp_Object str1, Lisp_Object start1, Lisp_Object end1, Lisp_Object str2, Lisp_Object start2, Lisp_Object end2, Lisp_Object ignore_case)
+  (Lisp_Object str1, Lisp_Object start1, Lisp_Object end1, Lisp_Object str2,
+   Lisp_Object start2, Lisp_Object end2, Lisp_Object ignore_case)
 {
-  register ptrdiff_t end1_char, end2_char;
-  register ptrdiff_t i1, i1_byte, i2, i2_byte;
+  EMACS_INT from1, to1, from2, to2;
+  ptrdiff_t i1, i1_byte, i2, i2_byte;
 
   CHECK_STRING (str1);
   CHECK_STRING (str2);
-  if (NILP (start1))
-    start1 = make_number (0);
-  if (NILP (start2))
-    start2 = make_number (0);
-  CHECK_NATNUM (start1);
-  CHECK_NATNUM (start2);
-  if (! NILP (end1))
-    CHECK_NATNUM (end1);
-  if (! NILP (end2))
-    CHECK_NATNUM (end2);
-
-  end1_char = SCHARS (str1);
-  if (! NILP (end1) && end1_char > XINT (end1))
-    end1_char = XINT (end1);
-  if (end1_char < XINT (start1))
-    args_out_of_range (str1, start1);
-
-  end2_char = SCHARS (str2);
-  if (! NILP (end2) && end2_char > XINT (end2))
-    end2_char = XINT (end2);
-  if (end2_char < XINT (start2))
-    args_out_of_range (str2, start2);
-
-  i1 = XINT (start1);
-  i2 = XINT (start2);
+
+  validate_subarray (str1, start1, end1, SCHARS (str1), &from1, &to1);
+  validate_subarray (str2, start2, end2, SCHARS (str2), &from2, &to2);
+
+  i1 = from1;
+  i2 = from2;
 
   i1_byte = string_char_to_byte (str1, i1);
   i2_byte = string_char_to_byte (str2, i2);
 
-  while (i1 < end1_char && i2 < end2_char)
+  while (i1 < to1 && i2 < to2)
     {
       /* When we find a mismatch, we must compare the
          characters, not just the bytes.  */
@@ -307,12 +292,8 @@ If string STR1 is greater, the value is a positive number N;
 
       if (! NILP (ignore_case))
         {
-          Lisp_Object tem;
-
-          tem = Fupcase (make_number (c1));
-          c1 = XINT (tem);
-          tem = Fupcase (make_number (c2));
-          c2 = XINT (tem);
+          c1 = XINT (Fupcase (make_number (c1)));
+          c2 = XINT (Fupcase (make_number (c2)));
         }
 
       if (c1 == c2)
@@ -322,15 +303,15 @@ If string STR1 is greater, the value is a positive number N;
          past the character that we are comparing;
          hence we don't add or subtract 1 here.  */
       if (c1 < c2)
-        return make_number (- i1 + XINT (start1));
+        return make_number (- i1 + from1);
       else
-        return make_number (i1 - XINT (start1));
+        return make_number (i1 - from1);
     }
 
-  if (i1 < end1_char)
-    return make_number (i1 - XINT (start1) + 1);
-  if (i2 < end2_char)
-    return make_number (- i1 + XINT (start1) - 1);
+  if (i1 < to1)
+    return make_number (i1 - from1 + 1);
+  if (i2 < to2)
+    return make_number (- i1 + from1 - 1);
 
   return Qt;
 }