From 42e68d71cfa149be195ddf8fce2f6e3b78f7d66a Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Tue, 2 Jan 2018 02:43:18 -0800
Subject: eliminate cdr_l use from implementation of last.

* lib.c (lastcons): Return value is just the last cons rather
than a loc. The only caller of this function is last.
(last): Adapt to the new lastcons.
---
 lib.c | 18 +++++++-----------
 lib.h |  2 +-
 2 files changed, 8 insertions(+), 12 deletions(-)

diff --git a/lib.c b/lib.c
index a48fb78a..fe8efbb6 100644
--- a/lib.c
+++ b/lib.c
@@ -664,26 +664,22 @@ loc term(loc head)
   return head;
 }
 
-loc lastcons(val list)
+val lastcons(val list)
 {
-  loc ret = nulloc;
-
+  val ret;
   gc_hint(list);
 
-  while (consp(cdr(list))) {
-    ret = cdr_l(list);
-    list = deref(ret);
-  }
+  for (ret = nil; consp(list); list = cdr(list))
+    ret = list;
+
   return ret;
 }
 
 val last(val seq, val n)
 {
   if (null_or_missing_p(n)) {
-    if (listp(seq)) {
-      loc p = lastcons(seq);
-      return nullocp(p) ? seq : deref(p);
-    }
+    if (listp(seq))
+      return lastcons(seq);
     return sub(seq, negone, t);
   } else {
     if (listp(seq))
diff --git a/lib.h b/lib.h
index 6ba0140c..f38314dc 100644
--- a/lib.h
+++ b/lib.h
@@ -537,7 +537,7 @@ val listref(val list, val ind);
 loc listref_l(val list, val ind);
 loc tail(val cons);
 loc term(loc head);
-loc lastcons(val list);
+val lastcons(val list);
 val last(val list, val n);
 val nthlast(val pos, val list);
 val nthcdr(val pos, val list);
-- 
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