From 99c17feac1cd1e5bb7d0b1d3b3793e2416f6f917 Mon Sep 17 00:00:00 2001
From: JeffBezanson <jeff.bezanson@gmail.com>
Date: Wed, 20 May 2009 18:52:09 +0000
Subject: [PATCH] made cons hashing tail recursive on cdrs plus one more test

---
 femtolisp/equal.c      | 33 ++++++++++++++++++---------------
 femtolisp/unittest.lsp |  8 ++++++++
 2 files changed, 26 insertions(+), 15 deletions(-)

diff --git a/femtolisp/equal.c b/femtolisp/equal.c
index 5cd6231..fe0eb3a 100644
--- a/femtolisp/equal.c
+++ b/femtolisp/equal.c
@@ -308,21 +308,24 @@ static uptrint_t bounded_hash(value_t a, int bound, int *oob)
         return h;
 
     case TAG_CONS:
-        if (bound <= 0) {
-            *oob = 1;
-            return 1;
-        }
-        h = bounded_hash(car_(a), bound/2, oob);
-        // bounds balancing: try to share the bounds efficiently
-        // between the car and cdr so we can hash better when a list is
-        // car-shallow and cdr-deep (a common case) or vice-versa.
-        if (*oob)
-            bound/=2;
-        else
-            bound--;
-        h = MIX(h, bounded_hash(cdr_(a), bound, &oob2)+2);
-        // recursive OOB propagation. otherwise this case is slow:
-        // (hash '#2=('#0=(#1=(#1#) . #0#) . #2#))
+        do {
+            if (bound <= 0) {
+                *oob = 1;
+                return h;
+            }
+            h = MIX(h, bounded_hash(car_(a), bound/2, &oob2));
+            // bounds balancing: try to share the bounds efficiently
+            // so we can hash better when a list is cdr-deep (a common case)
+            if (oob2)
+                bound/=2;
+            else
+                bound--;
+            // recursive OOB propagation. otherwise this case is slow:
+            // (hash '#2=((#0=(#1=(#1#) . #0#)) . #2#))
+            *oob = *oob || oob2;
+            a = cdr_(a);
+        } while (iscons(a));
+        h = MIX(h, bounded_hash(a, bound-1, &oob2)+2);
         *oob = *oob || oob2;
         return h;
     }
diff --git a/femtolisp/unittest.lsp b/femtolisp/unittest.lsp
index 5bba7a6..19064ac 100644
--- a/femtolisp/unittest.lsp
+++ b/femtolisp/unittest.lsp
@@ -130,6 +130,14 @@
 	      (hash '#0=((1 . #0#) . #0#))
 	      (hash '#1=((1 . #1#) (2 . #1#) . #1#)))))
 
+(assert (equal?
+	 (hash '(#0=(#0#) 0))
+	 (hash '(#1=(((((#1#))))) 0))))
+
+(assert (not (equal?
+	      (hash '(#0=(#0#) 0))
+	      (hash '(#1=(((((#1#))))) 1)))))
+
 (assert (equal?
 	 (hash #0=[1 [2 [#0#]] 3])
 	 (hash #1=[1 [2 [[1 [2 [#1#]] 3]]] 3])))