Re: Change a while loop into do while

[Paul Eggert <eggert@cs.ucla.edu>]

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> From: Chris Gregory <czipperz@gmail.com>
> Date: Mon, 26 Dec 2016 22:55:54 -0600
>
> This patch changes string_from_display_spec (a static function in
> xdisp.c) to use a do while loop instead of a while loop.  The
> precondition is checked by the if statement and is redundant in the
> first iteration.  This redundancy is now removed.

The indenting for 'do-while' wasn't using the usual GNU style, and while fixing 
that I noticed that the code could be further simplified, so I installed the 
attached further patch.

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From c48d410258353bc1ed8ec658ab69da2d67e1e8ea Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Sat, 31 Dec 2016 09:13:38 -0800
Subject: [PATCH] * src/xdisp.c (string_from_display_spec): Simplify.

---
 src/xdisp.c | 24 ++++++++----------------
 1 file changed, 8 insertions(+), 16 deletions(-)

diff --git a/src/xdisp.c b/src/xdisp.c
index 45a04ca..aced59e 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -1250,26 +1250,18 @@ default_line_pixel_height (struct window *w)
 static Lisp_Object
 string_from_display_spec (Lisp_Object spec)
 {
-  if (CONSP (spec))
+  if (VECTORP (spec))
     {
-      do {
-	if (STRINGP (XCAR (spec)))
-	  return XCAR (spec);
-	spec = XCDR (spec);
-      } while (CONSP (spec));
+      for (ptrdiff_t i = 0; i < ASIZE (spec); i++)
+	if (STRINGP (AREF (spec, i)))
+	  return AREF (spec, i);
     }
-  else if (VECTORP (spec))
+  else
     {
-      ptrdiff_t i;
-
-      for (i = 0; i < ASIZE (spec); i++)
-	{
-	  if (STRINGP (AREF (spec, i)))
-	    return AREF (spec, i);
-	}
-      return Qnil;
+      for (; CONSP (spec); spec = XCDR (spec))
+	if (STRINGP (XCAR (spec)))
+	  return XCAR (spec);
     }
-
   return spec;
 }
 
-- 
2.7.4