Add "buzzhash16" - a random hash function

This is just a toy. Probably not worth using in production. But
interesting enough I thought I would include it.

The idea is to use the hash seed as a table of random 16 bit integers
whose values are what we hash depending on the character we read.

It is pretty fast, I have no idea how secure it is. It will probably
work really badly if the seed is crap. YMMV.

1 files changed, 55 insertions, 2 deletions

diff --git a/hv.h b/hv.h
index 3f899e5362..26ad8a9858 100644
--- a/hv.h
+++ b/hv.h
@@ -129,6 +129,7 @@ struct xpvhv {
 #define PERL_HASH_SEED_U32   *((U32*)PERL_HASH_SEED)
 #define PERL_HASH_SEED_U64_1 (((U64*)PERL_HASH_SEED)[0])
 #define PERL_HASH_SEED_U64_2 (((U64*)PERL_HASH_SEED)[1])
+#define PERL_HASH_SEED_U16_x(idx) (((U16*)PERL_HASH_SEED)[idx])
 
 /* legacy - only mod_perl should be doing this.  */
 #ifdef PERL_HASH_INTERNAL_ACCESS
@@ -142,13 +143,65 @@ struct xpvhv {
 #define PERL_HASH_FUNC_MURMUR3
 #define PERL_HASH_FUNC_SIPHASH
 #define PERL_HASH_FUNC_ONE_AT_A_TIME
+#define PERL_HASH_FUNC_BUZZHASH16
 */
 
-#if !(defined(PERL_HASH_FUNC_SDBM) || defined(PERL_HASH_FUNC_DJB2) || defined(PERL_HASH_FUNC_SUPERFAST) || defined(PERL_HASH_FUNC_MURMUR3) || defined(PERL_HASH_FUNC_ONE_AT_A_TIME))
+#if !(defined(PERL_HASH_FUNC_SDBM) || defined(PERL_HASH_FUNC_DJB2) || defined(PERL_HASH_FUNC_SUPERFAST) \
+        || defined(PERL_HASH_FUNC_MURMUR3) || defined(PERL_HASH_FUNC_ONE_AT_A_TIME) || defined(PERL_HASH_FUNC_BUZZHASH16))
 #define PERL_HASH_FUNC_MURMUR3
 #endif
 
-#if defined(PERL_HASH_FUNC_SIPHASH)
+#if defined(PERL_HASH_FUNC_BUZZHASH16)
+/* "BUZZHASH16"
+ *
+ * I whacked this together while just playing around.
+ *
+ * The idea is that instead of hashing the actual string input we use the
+ * bytes of the string as an index into a table of randomly generated
+ * 16 bit values.
+ *
+ * A left rotate is used to "mix" in previous bits as we go, and I borrowed
+ * the avalanche function from one-at-a-time for the final step. A lookup
+ * into the table based on the lower 8 bits of the length combined with
+ * the length itself is used as an itializer.
+ *
+ * The resulting hash value has no actual bits fed in from the string so
+ * I would guess it is pretty secure, although I am not a cryptographer
+ * and have no idea for sure. Nor has it been rigorously tested. On the
+ * other hand it is reasonably fast, and seems to produce reasonable
+ * distributions.
+ *
+ * Yves Orton
+ */
+
+
+#define PERL_HASH_FUNC "BUZZHASH16"
+#define PERL_HASH_SEED_BYTES 512 /* 2 bytes per octet value, 2 * 256 */
+/* Find best way to ROTL32 */
+#if defined(_MSC_VER)
+  #include <stdlib.h>  /* Microsoft put _rotl declaration in here */
+  #define BUZZHASH_ROTL32(x,r)  _rotl(x,r)
+#else
+  /* gcc recognises this code and generates a rotate instruction for CPUs with one */
+  #define BUZZHASH_ROTL32(x,r)  (((U32)x << r) | ((U32)x >> (32 - r)))
+#endif
+
+#define PERL_HASH(hash,str,len) \
+     STMT_START        { \
+        register const char * const s_PeRlHaSh_tmp = (str); \
+        register const unsigned char *s_PeRlHaSh = (const unsigned char *)s_PeRlHaSh_tmp; \
+        register const unsigned char *end_PeRlHaSh = (const unsigned char *)s_PeRlHaSh + len; \
+        register U32 hash_PeRlHaSh = (PERL_HASH_SEED_U16_x(len & 0xff) << 16) + len; \
+        while (s_PeRlHaSh < end_PeRlHaSh) { \
+            hash_PeRlHaSh ^= PERL_HASH_SEED_U16_x((U8)*s_PeRlHaSh++); \
+            hash_PeRlHaSh += BUZZHASH_ROTL32(hash_PeRlHaSh,11); \
+        } \
+        hash_PeRlHaSh += (hash_PeRlHaSh << 3); \
+        hash_PeRlHaSh ^= (hash_PeRlHaSh >> 11); \
+        (hash) = (hash_PeRlHaSh + (hash_PeRlHaSh << 15)); \
+    } STMT_END
+
+#elif defined(PERL_HASH_FUNC_SIPHASH)
 #define PERL_HASH_FUNC "SIPHASH"
 #define PERL_HASH_SEED_BYTES 16