From ab28b8b9fd5e402c80aef0874ca35895dde858c5 Mon Sep 17 00:00:00 2001
From: Willy Tarreau <w@1wt.eu>
Date: Sun, 9 Sep 2007 21:13:47 +0200
Subject: [PATCH] [TESTS] added a new hash algorithm

added "wt_hash" which shows only 60 collisions in 575k values, which
sets it between hashword() and djbx33(). It's also between both in
terms of performance, but the most important part is that its variable
length rotation mechanism should make it really harder to predict and
attack than the other ones.
---
 tests/test_hashes.c | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

diff --git a/tests/test_hashes.c b/tests/test_hashes.c
index baac40479..39cb965f3 100644
--- a/tests/test_hashes.c
+++ b/tests/test_hashes.c
@@ -158,10 +158,6 @@ ub4 bernstein(ub1 *key, ub4 len, ub4 level){
                        +(uint32_t)(((const uint8_t *)(d))[0]) )
 #endif
 
-/*
- * This function has a hole of 11 unused bits in bytes 2 and 3 of each block of
- * 32 bits.
- */
 uint32_t SuperFastHash (const char * data, int len) {
 uint32_t hash = len, tmp;
 int rem;
@@ -208,7 +204,7 @@ int rem;
 }
 
 /*
- * This variant uses all bits from the input block, and is about 15% faster.
+ * This variant is about 15% faster.
  */
 uint32_t SuperFastHash2 (const char * data, int len) {
 uint32_t hash = len, tmp;
@@ -224,7 +220,7 @@ int rem;
 	register uint32_t next;
 	next   = get16bits(data+2);
         hash  += get16bits(data);
-        tmp    = ((next << 11) | (next >> 21)) ^ hash;
+        tmp    = (next << 11) ^ hash;
         hash   = (hash << 16) ^ tmp;
         data  += 2*sizeof (uint16_t);
         hash  += hash >> 11;
@@ -493,6 +489,23 @@ unsigned oat_hash ( void *key, int len )
   return h;
 }
 
+unsigned wt_hash ( void *key, int len )
+{
+  unsigned char *p = key;
+  unsigned h = 0x783c965aUL;
+  unsigned step = 16;
+
+  for (; len > 0; len--) {
+      h ^= *p * 9;
+      p++;
+      h = (h << step) | (h >> (32-step));
+      step ^= h;
+      step &= 0x1F;
+  }
+
+  return h;
+}
+
 
 #define run_test(fct, args) {						\
     unsigned long loop, count;						\
@@ -526,6 +539,7 @@ int main(){
   start = urls;
   len = strlen(*urls);
 
+  run_test(wt_hash, (*urls, len));
   run_test(SuperFastHash2, (*urls, len));
   run_test(SuperFastHash, (*urls, len));
   run_test(haproxy_uri_hash, (*urls, len));