Added a function to combine hashvalues and produce a third one of them.

[r6238]

diff --git a/ir/adt/hashptr.h b/ir/adt/hashptr.h
index ff325c7..5755b3e 100644 (file)
--- a/ir/adt/hashptr.h
+++ b/ir/adt/hashptr.h
@@ -17,13 +17,17 @@
 #define _FIRM_FNV_OFFSET_BASIS 2166136261U
 #define _FIRM_FNV_FNV_PRIME 16777619U
 
+/* Computing x * _FIRM_FNV_FNV_PRIME */
+#define _FIRM_FNV_TIMES_PRIME(x) \
+  (((x) << 24) + ((x) << 8) + ((x) << 7) + ((x) << 4) + ((x) << 1) + 1)
+
 static INLINE unsigned firm_fnv_hash(const unsigned char *data, unsigned bytes)
 {
        unsigned i;
        unsigned hash = _FIRM_FNV_OFFSET_BASIS;
 
        for(i = 0; i < bytes; ++i) {
-               hash *= _FIRM_FNV_FNV_PRIME;
+               hash = _FIRM_FNV_TIMES_PRIME(hash);
                hash ^= data[i];
        }
 
@@ -44,4 +48,21 @@ static INLINE unsigned firm_fnv_hash(const unsigned char *data, unsigned bytes)
  */
 #define HASH_STR(str,len) firm_fnv_hash((const unsigned char *) (str), (len))
 
+static INLINE unsigned _hash_combine(unsigned x, unsigned y)
+{
+  unsigned hash = _FIRM_FNV_TIMES_PRIME(_FIRM_FNV_OFFSET_BASIS);
+  hash ^= x;
+  hash  = _FIRM_FNV_TIMES_PRIME(hash);
+  hash ^= y;
+  return hash;
+}
+
+/**
+ * Make one hash value out of two others.
+ * @param a One hash value.
+ * @param b Another hash value.
+ * @return A hash value computed from the both.
+ */
+#define HASH_COMBINE(a,b) _hash_combine(a, b)
+
 #endif /* __HASHPTR_H__ */