[Patch, libgfortran] Better format hash function

[Janne Blomqvist <blomqvist dot janne at gmail dot com>]

Hi,

the attached patch replaces the existing (too?) simple string hash
function with an almost equally simple but supposedly pretty well
working one by D.J. Bernstein.

Regtested on x86_64-unknown-linux-gnu, Ok for trunk?

-- 
Janne Blomqvist

Attachment: ChangeLog
Description: Binary data

diff --git a/libgfortran/io/format.c b/libgfortran/io/format.c
index 2c116d6..886b524 100644
--- a/libgfortran/io/format.c
+++ b/libgfortran/io/format.c
@@ -141,14 +141,15 @@ uint32_t format_hash (st_parameter_dt *dtp)
 {
   char *key;
   gfc_charlen_type key_len;
-  uint32_t hash = 0;
+  uint32_t hash = 5381;
   gfc_charlen_type i;
 
-  /* Hash the format string. Super simple, but what the heck!  */
+  /* Hash the format string. Uses the DJB algorithm, which is simple
+     but is supposed to work well.  */
   key = dtp->format;
   key_len = dtp->format_len;
   for (i = 0; i < key_len; i++)
-    hash ^= key[i];
+    hash = ((hash << 5) + hash) + key[i]; /* hash = hash * 33 + key[i]  */
   hash &= (FORMAT_HASH_SIZE - 1);
   return hash;
 }