hv_func.h - fix seed initialization in sdbm and djb2 hashing algorithms.

In a previous commit I added code to "mix in" the length of the
string into the seed used by these functions, to avoid issues with
zero seeds, and with the hope that it makes it harder to create
multicollision attacks against these hash functions.

Unfortunately when I restructured the seed logic for the inline
functions in hv_func.h I messed it up, and these hash functions
were broken. I never noticed because they are both such bad hash
functions for our needs that I never built with them, and we have
no infrastructure to make it easy to test building with non-standard
hash functions so it never got automatically tested. Hopefully
at some point someone will find a round-tuit and teach Configure
about selecting alternate hash functions.

diff --git a/hv_func.h b/hv_func.h
index 53230ae..473ec46 100644 (file)
--- a/hv_func.h
+++ b/hv_func.h
@@ -455,7 +455,7 @@ S_perl_hash_murmur3(const unsigned char * const seed, const unsigned char *ptr,
 PERL_STATIC_INLINE U32
 S_perl_hash_djb2(const unsigned char * const seed, const unsigned char *str, const STRLEN len) {
     const unsigned char * const end = (const unsigned char *)str + len;
-    U32 hash = *((U32*)seed + len);
+    U32 hash = *((U32*)seed) + len;
     while (str < end) {
         hash = ((hash << 5) + hash) + *str++;
     }
@@ -465,7 +465,7 @@ S_perl_hash_djb2(const unsigned char * const seed, const unsigned char *str, con
 PERL_STATIC_INLINE U32
 S_perl_hash_sdbm(const unsigned char * const seed, const unsigned char *str, const STRLEN len) {
     const unsigned char * const end = (const unsigned char *)str + len;
-    U32 hash = *((U32*)seed + len);
+    U32 hash = *((U32*)seed) + len;
     while (str < end) {
         hash = (hash << 6) + (hash << 16) - hash + *str++;
     }