X-Git-Url: https://git.hcoop.net/bpt/guile.git/blobdiff_plain/9b977c836bf147d386944c401113aba32776fa68..1f3babaaef5f4c41c24615035a9549e2faf2605e:/libguile/list.c

diff --git a/libguile/list.c b/libguile/list.c
index 627640334..27ac22f2b 100644
--- a/libguile/list.c
+++ b/libguile/list.c
@@ -1,5 +1,5 @@
-/* Copyright (C) 1995,1996,1997,2000,2001,2003,2004,2008,2009,2010,2011
- * Free Software Foundation, Inc.
+/* Copyright (C) 1995-1997, 2000, 2001, 2003, 2004, 2008-2011,
+ *   2014 Free Software Foundation, Inc.
  * 
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public License
@@ -179,24 +179,25 @@ SCM_DEFINE (scm_list_p, "list?", 1, 0, 0,
    long" lists (i.e. lists with cycles in their cdrs), and returns -1
    if it does find one.  */
 long
-scm_ilength(SCM sx)
+scm_ilength (SCM sx)
 {
   long i = 0;
   SCM tortoise = sx;
   SCM hare = sx;
 
-  do {
-    if (SCM_NULL_OR_NIL_P(hare)) return i;
-    if (!scm_is_pair (hare)) return -1;
-    hare = SCM_CDR(hare);
-    i++;
-    if (SCM_NULL_OR_NIL_P(hare)) return i;
-    if (!scm_is_pair (hare)) return -1;
-    hare = SCM_CDR(hare);
-    i++;
-    /* For every two steps the hare takes, the tortoise takes one.  */
-    tortoise = SCM_CDR(tortoise);
-  }
+  do
+    {
+      if (!scm_is_pair (hare))
+        return SCM_NULL_OR_NIL_P (hare) ? i : -1;
+      hare = SCM_CDR (hare);
+      i++;
+      if (!scm_is_pair (hare))
+        return SCM_NULL_OR_NIL_P (hare) ? i : -1;
+      hare = SCM_CDR (hare);
+      i++;
+      /* For every two steps the hare takes, the tortoise takes one.  */
+      tortoise = SCM_CDR (tortoise);
+    }
   while (!scm_is_eq (hare, tortoise));
 
   /* If the tortoise ever catches the hare, then the list must contain
@@ -374,20 +375,49 @@ SCM_DEFINE (scm_reverse_x, "reverse!", 1, 1, 0,
 	    "@code{reverse!}")
 #define FUNC_NAME s_scm_reverse_x
 {
-  SCM_VALIDATE_LIST (1, lst);
+  SCM old_lst = lst;
+  SCM tail = SCM_BOOL_F;
+
   if (SCM_UNBNDP (new_tail))
     new_tail = SCM_EOL;
-  else
-    SCM_VALIDATE_LIST (2, new_tail);
 
-  while (!SCM_NULL_OR_NIL_P (lst))
+  if (SCM_NULL_OR_NIL_P (lst))
+    return new_tail;
+
+  /* SCM_VALIDATE_LIST would run through the whole list to make sure it
+     is not eventually circular.  In contrast to most list operations,
+     reverse! cannot get stuck in an infinite loop but arrives back at
+     the start when given an eventually or fully circular list.  Because
+     of that, we can save the cost of an upfront proper list check at
+     the price of having to do a double reversal in the error case.
+  */
+
+  while (scm_is_pair (lst))
     {
       SCM old_tail = SCM_CDR (lst);
-      SCM_SETCDR (lst, new_tail);
-      new_tail = lst;
+      SCM_SETCDR (lst, tail);
+      tail = lst;
       lst = old_tail;
     }
-  return new_tail;
+
+  if (SCM_LIKELY (SCM_NULL_OR_NIL_P (lst)))
+    {
+      SCM_SETCDR (old_lst, new_tail);
+      return tail;
+    }
+
+  /* We did not start with a proper list.  Undo the reversal. */
+
+  while (scm_is_pair (tail))
+    {
+      SCM old_tail = SCM_CDR (tail);
+      SCM_SETCDR (tail, lst);
+      lst = tail;
+      tail = old_tail;
+    }
+
+  SCM_WRONG_TYPE_ARG (1, lst);
+  return lst;
 }
 #undef FUNC_NAME