(mm-string-to-multibyte): New function.

(mm-detect-coding-region): Typo.

2 files changed, 26 insertions, 2 deletions

diff --git a/lisp/gnus/ChangeLog b/lisp/gnus/ChangeLog
index 7eb877a669f..052a7fdf5fc 100644
--- a/lisp/gnus/ChangeLog
+++ b/lisp/gnus/ChangeLog
@@ -1,3 +1,8 @@
+2005-04-10  Stefan Monnier  <monnier@iro.umontreal.ca>
+
+        * mm-util.el (mm-string-to-multibyte): New function.
+        (mm-detect-coding-region): Typo.
+
 2005-04-06  Katsumi Yamaoka  <yamaoka@jpl.org>
 
         * mm-util.el (mm-coding-system-p): Don't return binary for the nil
diff --git a/lisp/gnus/mm-util.el b/lisp/gnus/mm-util.el
index b8a739eeed6..0ee52e797d0 100644
--- a/lisp/gnus/mm-util.el
+++ b/lisp/gnus/mm-util.el
@@ -72,7 +72,26 @@
             string)))
      (string-as-unibyte . identity)
      (string-make-unibyte . identity)
+     ;; string-as-multibyte often doesn't really do what you think it does.
+     ;; Example:
+     ;;    (aref (string-as-multibyte "\201") 0) -> 129 (aka ?\201)
+     ;;    (aref (string-as-multibyte "\300") 0) -> 192 (aka ?\300)
+     ;;    (aref (string-as-multibyte "\300\201") 0) -> 192 (aka ?\300)
+     ;;    (aref (string-as-multibyte "\300\201") 1) -> 129 (aka ?\201)
+     ;; but
+     ;;    (aref (string-as-multibyte "\201\300") 0) -> 2240
+     ;;    (aref (string-as-multibyte "\201\300") 1) -> <error>
+     ;; Better use string-to-multibyte or encode-coding-string.
+     ;; If you really need string-as-multibyte somewhere it's usually
+     ;; because you're using the internal emacs-mule representation (maybe
+     ;; because you're using string-as-unibyte somewhere), which is
+     ;; generally a problem in itself.
+     ;; Here is an approximate equivalence table to help think about it:
+     ;; (string-as-multibyte s)   ~= (decode-coding-string s 'emacs-mule)
+     ;; (string-to-multibyte s)   ~= (decode-coding-string s 'binary)
+     ;; (string-make-multibyte s) ~= (decode-coding-string s locale-coding-system)
      (string-as-multibyte . identity)
+     (string-to-multibyte . mm-string-as-multibyte)
      (multibyte-string-p . ignore)
      ;; It is not a MIME function, but some MIME functions use it.
      (make-temp-file . (lambda (prefix &optional dir-flag)
@@ -938,7 +957,7 @@ If INHIBIT is non-nil, inhibit `mm-inhibit-file-name-handlers'."
     (defun mm-detect-coding-region (start end)
       "Like `detect-coding-region' except returning the best one."
       (let ((coding-systems
-             (detect-coding-region (point) (point-max))))
+             (detect-coding-region start end)))
         (or (car-safe coding-systems)
             coding-systems)))
   (defun mm-detect-coding-region (start end)
@@ -962,5 +981,5 @@ If INHIBIT is non-nil, inhibit `mm-inhibit-file-name-handlers'."
 
 (provide 'mm-util)
 
-;;; arch-tag: 94dc5388-825d-4fd1-bfa5-2100aa351238
+;; arch-tag: 94dc5388-825d-4fd1-bfa5-2100aa351238
 ;;; mm-util.el ends here