# HG changeset patch
# User Aidan Kehoe <kehoea@parhasard.net>
# Date 1200493251 -3600
# Node ID 479443c0f95a6291466173eb0254f61681654c9c
# Parent  9e28067e3083ce90cdd48370cd9f7947862681f9
Have list hashes depend on the order of the contents, as is the case for vectors.

src/ChangeLog addition:

2008-01-16  Aidan Kehoe  <kehoea@parhasard.net>

	* elhash.c (internal_hash):
	Make short lists with the same contents in a different order hash
	distinctly. Gives better performance for things like three-element
	lists describing colours. Thank you Sebastian Freundt!

tests/ChangeLog addition:

2008-01-16  Aidan Kehoe  <kehoea@parhasard.net>

	* automated/hash-table-tests.el:
	Assert that two short lists with the same contents in distinct
	orders hash differently.

diff -r 9e28067e3083 -r 479443c0f95a src/ChangeLog
--- a/src/ChangeLog	Wed Jan 16 00:19:59 2008 +0100
+++ b/src/ChangeLog	Wed Jan 16 15:20:51 2008 +0100
@@ -1,3 +1,10 @@
+2008-01-16  Aidan Kehoe  <kehoea@parhasard.net>
+
+	* elhash.c (internal_hash):
+	Make short lists with the same contents in a different order hash
+	distinctly. Gives better performance for things like three-element
+	lists describing colours. Thank you Sebastian Freundt!
+
 2008-01-15  Aidan Kehoe  <kehoea@parhasard.net>
 
 	* print.c (prin1_to_string): New.
diff -r 9e28067e3083 -r 479443c0f95a src/elhash.c
--- a/src/elhash.c	Wed Jan 16 00:19:59 2008 +0100
+++ b/src/elhash.c	Wed Jan 16 15:20:51 2008 +0100
@@ -1719,12 +1719,33 @@
 {
   if (depth > 5)
     return 0;
-  if (CONSP (obj))
+
+  if (CONSP(obj)) 
     {
-      /* no point in worrying about tail recursion, since we're not
-	 going very deep */
-      return HASH2 (internal_hash (XCAR (obj), depth + 1),
-		    internal_hash (XCDR (obj), depth + 1));
+      Hashcode hash, h;
+      int s;
+
+      depth += 1;
+
+      if (!CONSP(XCDR(obj)))
+	{
+	  /* special case for '(a . b) conses */
+	  return HASH2(internal_hash(XCAR(obj), depth),
+		       internal_hash(XCDR(obj), depth));
+	}
+
+      /* Don't simply tail recurse; we want to hash lists with the
+	 same contents in distinct orders differently. */
+      hash = internal_hash(XCAR(obj), depth);
+
+      obj = XCDR(obj);
+      for (s = 1; s < 6 && CONSP(obj); obj = XCDR(obj), s++)
+	{
+	  h = internal_hash(XCAR(obj), depth);
+	  hash = HASH3(hash, h, s);
+	}
+
+      return hash;
     }
   if (STRINGP (obj))
     {
diff -r 9e28067e3083 -r 479443c0f95a tests/ChangeLog
--- a/tests/ChangeLog	Wed Jan 16 00:19:59 2008 +0100
+++ b/tests/ChangeLog	Wed Jan 16 15:20:51 2008 +0100
@@ -1,3 +1,9 @@
+2008-01-16  Aidan Kehoe  <kehoea@parhasard.net>
+
+	* automated/hash-table-tests.el: 
+	Assert that two short lists with the same contents in distinct
+	orders hash differently. 
+
 2008-01-15  Aidan Kehoe  <kehoea@parhasard.net>
 
 	* automated/lisp-tests.el (literal-with-uninterned):
diff -r 9e28067e3083 -r 479443c0f95a tests/automated/hash-table-tests.el
--- a/tests/automated/hash-table-tests.el	Wed Jan 16 00:19:59 2008 +0100
+++ b/tests/automated/hash-table-tests.el	Wed Jan 16 15:20:51 2008 +0100
@@ -281,3 +281,4 @@
 ;;; Test sxhash
 (Assert (= (sxhash "foo") (sxhash "foo")))
 (Assert (= (sxhash '(1 2 3)) (sxhash '(1 2 3))))
+(Assert (/= (sxhash '(1 2 3)) (sxhash '(3 2 1))))