Prefer format-time-string to current-time-string

* lisp/arc-mode.el (archive-unixdate):
* lisp/gnus/nnrss.el (nnrss-normalize-date):
* lisp/tar-mode.el (tar-clip-time-string):
Prefer format-time-string to reassembling current-time-string output.

doc/lispref/os.texi

@@ -1352,7 +1352,7 @@ may change as higher-resolution clocks become available.
 
 @cindex time value
   Function arguments, e.g., the @var{time} argument to
-@code{current-time-string}, accept a more-general @dfn{time value}
+@code{format-time-string}, accept a more-general @dfn{time value}
 format, which can be a Lisp timestamp, @code{nil} for the current
 time, a single floating-point number for seconds, or a list
 @code{(@var{high} @var{low} @var{micro})} or @code{(@var{high}

lisp/arc-mode.el

@@ -617,12 +617,8 @@ OLDMODE will be modified accordingly just like chmod(2) would have done."
 
 (defun archive-unixdate (low high)
   "Stringify Unix (LOW HIGH) date."
-  (let* ((time (list high low))
-	 (str (current-time-string time)))
-    (format "%s-%s-%s"
-	    (substring str 8 10)
-	    (substring str 4 7)
-	    (format-time-string "%Y" time))))
+  (let ((system-time-locale "C"))
+    (format-time-string "%e-%b-%Y" (list high low))))
 
 (defun archive-unixtime (low high)
   "Stringify Unix (LOW HIGH) time."

lisp/gnus/nnrss.el

@@ -450,7 +450,7 @@ nnrss: %s: Not valid XML %s and libxml-parse-html-region doesn't work %s"
 This function handles the ISO 8601 date format described in
 URL `https://www.w3.org/TR/NOTE-datetime', and also the RFC 822 style
 which RSS 2.0 allows."
-  (let (case-fold-search vector year month day time zone cts given)
+  (let (case-fold-search vector year month day time zone given)
     (cond ((null date))			; do nothing for this case
 	  ;; if the date is just digits (unix time stamp):
 	  ((string-match "^[0-9]+$" date)
@@ -481,13 +481,13 @@ which RSS 2.0 allows."
 			    0
 			  (decoded-time-zone decoded))))))
     (if month
-	(progn
-	  (setq cts (current-time-string (encode-time 0 0 0 day month year)))
-	  (format "%s, %02d %s %04d %s%s"
-		  (substring cts 0 3) day (substring cts 4 7) year time
-		  (if zone
-		      (concat " " (format-time-string "%z" nil zone))
-		    "")))
+	(concat (let ((system-time-locale "C"))
+		  (format-time-string "%a, %d %b %Y "
+				      (encode-time 0 0 0 day month year)))
+		time
+		(if zone
+		    (format-time-string " %z" nil zone)
+		  ""))
       (message-make-date given))))
 
 ;;; data functions

lisp/tar-mode.el

@@ -467,8 +467,8 @@ checksum before doing the check."
 
 (defun tar-clip-time-string (time)
   (declare (obsolete format-time-string "27.1"))
-  (let ((str (current-time-string time)))
-    (concat " " (substring str 4 16) (format-time-string " %Y" time))))
+  (let ((system-time-locale "C"))
+    (format-time-string " %b %e %H:%M %Y" time)))
 
 (defun tar-grind-file-mode (mode)
   "Construct a `rw-r--r--' string indicating MODE.