1 files changed, 103 insertions, 0 deletions
diff --git a/libglusterfs/src/hashfn.c b/libglusterfs/src/hashfn.c
index 810cc92495e..9ef8955a87d 100644
--- a/libglusterfs/src/hashfn.c
+++ b/libglusterfs/src/hashfn.c
@@ -29,6 +29,10 @@
 
 #define get16bits(d) (*((const uint16_t *) (d)))
 
+#define DM_DELTA 0x9E3779B9
+#define DM_FULLROUNDS 10        /* 32 is overkill, 16 is strong crypto */
+#define DM_PARTROUNDS 6	        /* 6 gets complete mixing */
+
 /*
   This is apparently the "fastest hash function for strings".
   Written by Paul Hsieh <http://www.azillionmonkeys.com/qed/hash.html>
@@ -87,3 +91,102 @@ uint32_t SuperFastHash (const char * data, int32_t len) {
 
   return hash;
 }
+
+
+/* Davies-Meyer hashing function implementation
+ */
+static int
+dm_round (int rounds, uint32_t *array, uint32_t *h0, uint32_t *h1)
+{
+	uint32_t sum = 0;
+	int      n = 0;
+	uint32_t b0  = 0;
+	uint32_t b1  = 0;
+
+	b0 = *h0;
+	b1 = *h1;
+
+	n = rounds;
+
+	do {
+		sum += DM_DELTA;
+		b0  += ((b1 << 4) + array[0])
+			^ (b1 + sum)
+			^ ((b1 >> 5) + array[1]);
+		b1  += ((b0 << 4) + array[2])
+			^ (b0 + sum)
+			^ ((b0 >> 5) + array[3]);
+	} while (--n);
+
+	*h0 += b0;
+	*h1 += b1;
+
+	return 0;
+}
+
+
+uint32_t
+__pad (int len)
+{
+	uint32_t pad = 0;
+
+	pad = (uint32_t) len | ((uint32_t) len << 8);
+	pad |= pad << 16;
+
+	return pad;
+}
+
+uint32_t
+gf_dm_hashfn (const char *msg, int len)
+{
+	uint32_t  h0 = 0x9464a485;
+	uint32_t  h1 = 0x542e1a94;
+	uint32_t  array[4];
+	uint32_t  pad = 0;
+	int       i = 0;
+	int       j = 0;
+	int       full_quads = 0;
+	int       full_words = 0;
+	int       full_bytes = 0;
+	uint32_t *intmsg = NULL;
+	int       word = 0;
+
+
+	intmsg = (uint32_t *) msg;
+	pad = __pad (len);
+
+	full_bytes   = len;
+	full_words   = len / 4;
+	full_quads   = len / 16;
+
+	for (i = 0; i < full_quads; i++) {
+		for (j = 0; j < 4; j++) {
+			word     = *intmsg;
+			array[j] = word;
+			intmsg++;
+			full_words--;
+			full_bytes -= 4;
+		}
+		dm_round (DM_PARTROUNDS, &array[0], &h0, &h1);
+	}
+
+	for (j = 0; j < 4; j++) {
+		if (full_words) {
+			word     = *intmsg;
+			array[j] = word;
+			intmsg++;
+			full_words--;
+			full_bytes -= 4;
+		} else {
+			array[j] = pad;
+			while (full_bytes) {
+				array[j] <<= 8;
+				array[j] |= msg[len - full_bytes];
+				full_bytes--;
+			}
+		}
+	}
+	dm_round (DM_FULLROUNDS, &array[0], &h0, &h1);
+
+	return h0 ^ h1;
+}