[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.

diff --git a/tests/test_hashes.c b/tests/test_hashes.c
index baac404..39cb965 100644 (file)
--- 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));