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[Guile-commits] GNU Guile branch, stable-2.0, updated. v2.0.11-2-g0ece48
From: |
Mark H Weaver |
Subject: |
[Guile-commits] GNU Guile branch, stable-2.0, updated. v2.0.11-2-g0ece485 |
Date: |
Tue, 01 Apr 2014 16:32:12 +0000 |
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http://git.savannah.gnu.org/cgit/guile.git/commit/?id=0ece4850c5423d53db3245f57681053486327aa3
The branch, stable-2.0 has been updated
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from 8d124d207738be0b43dfc235a5d72519a2ab5db9 (commit)
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- Log -----------------------------------------------------------------
commit 0ece4850c5423d53db3245f57681053486327aa3
Author: David Kastrup <address@hidden>
Date: Tue Apr 1 16:24:29 2014 +0200
Make reverse! forego the cost of SCM_VALIDATE_LIST
* libguile/list.c (scm_reverse_x): Do not validate first argument to
reverse! in advance. Instead undo reversal in error case.
Signed-off-by: David Kastrup <address@hidden>
Signed-off-by: Mark H Weaver <address@hidden>
-----------------------------------------------------------------------
Summary of changes:
libguile/list.c | 41 ++++++++++++++++++++++++++++++++++++-----
1 files changed, 36 insertions(+), 5 deletions(-)
diff --git a/libguile/list.c b/libguile/list.c
index d30f9e8..01f23c0 100644
--- a/libguile/list.c
+++ b/libguile/list.c
@@ -374,18 +374,49 @@ 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;
- 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
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Mark H Weaver <=