From 5255fd1f36eece1cbf4000ffc3120dbcb9bf5038 Mon Sep 17 00:00:00 2001
From: "H. Peter Anvin" <hpa@zytor.com>
Date: Tue, 18 Sep 2007 12:38:07 -0700
Subject: Change the token prehash function for better convergence

Combining arithmetric (add) and bitwise (xor) mixing seems to give
better result than either.

With the new prehash function, we find a valid hash much quicker.
---
 perllib/phash.ph | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

(limited to 'perllib')

diff --git a/perllib/phash.ph b/perllib/phash.ph
index 6033427..3bb3a05 100644
--- a/perllib/phash.ph
+++ b/perllib/phash.ph
@@ -42,8 +42,8 @@ sub prehash($$$) {
 
     foreach $c (unpack("C*", $key)) {
 	$ko1 = $k1;  $ko2 = $k2;
-	$k1 = int32(rot($ko1,$s0)-rot($ko2, $s1)+$c);
-	$k2 = int32(rot($ko2,$s2)-rot($ko1, $s3)+$c);
+	$k1 = int32(rot($ko1,$s0)^int32(rot($ko2, $s1)+$c));
+	$k2 = int32(rot($ko2,$s2)^int32(rot($ko1, $s3)+$c));
     }
 
     # Create a bipartite graph...
-- 
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