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-rw-r--r--libglusterfs/src/hashfn.c103
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;
+}