From: Ben Pfaff <blp@nicira.com>
Date: Tue, 6 Jan 2009 20:55:14 +0000 (-0800)
Subject: Add lookup3-based hash for bytes, and remove FNV hash entirely.
X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=967da83e032e31f1cf680ffacab1cc46565411cf;p=openvswitch

Add lookup3-based hash for bytes, and remove FNV hash entirely.

The lookup3 hash is superior to FNV.  This change makes OpenFlow use
lookup3 exclusively, by adding a variant of it that can hash arbitrary
byte sequences.
---

diff --git a/lib/flow.h b/lib/flow.h
index 63974c45..99b5752c 100644
--- a/lib/flow.h
+++ b/lib/flow.h
@@ -1,4 +1,4 @@
-/* Copyright (c) 2008 The Board of Trustees of The Leland Stanford
+/* Copyright (c) 2008, 2009 The Board of Trustees of The Leland Stanford
  * Junior University
  * 
  * We are making the OpenFlow specification and associated documentation
@@ -82,8 +82,8 @@ static inline size_t
 flow_hash(const struct flow *flow, uint32_t basis)
 {
     BUILD_ASSERT_DECL(!(sizeof *flow % sizeof(uint32_t)));
-    return hash_lookup3((const uint32_t *) flow,
-                        sizeof *flow / sizeof(uint32_t), basis);
+    return hash_words((const uint32_t *) flow,
+                      sizeof *flow / sizeof(uint32_t), basis);
 }
 
 #endif /* flow.h */
diff --git a/lib/hash.c b/lib/hash.c
index 22caa923..104ce224 100644
--- a/lib/hash.c
+++ b/lib/hash.c
@@ -1,4 +1,4 @@
-/* Copyright (c) 2008 The Board of Trustees of The Leland Stanford
+/* Copyright (c) 2008, 2009 The Board of Trustees of The Leland Stanford
  * Junior University
  * 
  * We are making the OpenFlow specification and associated documentation
@@ -32,18 +32,7 @@
  */
 #include <config.h>
 #include "hash.h"
-
-uint32_t
-hash_fnv(const void *p_, size_t n, uint32_t basis)
-{
-    const uint8_t *p = p_;
-    uint32_t hash = basis;
-    while (n--) {
-        hash *= HASH_FNV_PRIME;
-        hash ^= *p++;
-    }
-    return hash;
-}
+#include <string.h>
 
 /* This is the public domain lookup3 hash by Bob Jenkins from
  * http://burtleburtle.net/bob/c/lookup3.c, modified for style. */
@@ -70,11 +59,10 @@ hash_fnv(const void *p_, size_t n, uint32_t basis)
       c ^= b; c -= rot(b, 24);                  \
     } while (0)
 
-/* Returns the hash of the 'n' uint32_t values at 'p', starting from 'basis'.
- * Note especially that 'n' is a count of 32-bit words, not bytes, and that
+/* Returns the hash of the 'n' 32-bit words at 'p', starting from 'basis'.
  * 'p' must be properly aligned. */
 uint32_t
-hash_lookup3(const uint32_t *p, size_t n, uint32_t basis)
+hash_words(const uint32_t *p, size_t n, uint32_t basis)
 {
     uint32_t a, b, c;
 
@@ -106,3 +94,34 @@ hash_lookup3(const uint32_t *p, size_t n, uint32_t basis)
     return c;
 }
 
+/* Returns the hash of the 'n' bytes at 'p', starting from 'basis'. */
+uint32_t
+hash_bytes(const void *p_, size_t n, uint32_t basis)
+{
+    const uint8_t *p = p_;
+    uint32_t a, b, c;
+    uint32_t tmp[3];
+
+    a = b = c = 0xdeadbeef + n + basis;
+
+    while (n >= sizeof tmp) {
+        memcpy(tmp, p, sizeof tmp);
+        a += tmp[0];
+        b += tmp[1];
+        c += tmp[2];
+        mix(a, b, c);
+        n -= sizeof tmp;
+        p += sizeof tmp;
+    }
+
+    if (n) {
+        tmp[0] = tmp[1] = tmp[2] = 0;
+        memcpy(tmp, p, n);
+        a += tmp[0];
+        b += tmp[1];
+        c += tmp[2];
+        final(a, b, c);
+    }
+
+    return c;
+}
diff --git a/lib/hash.h b/lib/hash.h
index 44d7b054..a52d8ca7 100644
--- a/lib/hash.h
+++ b/lib/hash.h
@@ -1,4 +1,4 @@
-/* Copyright (c) 2008 The Board of Trustees of The Leland Stanford
+/* Copyright (c) 2008, 2009 The Board of Trustees of The Leland Stanford
  * Junior University
  * 
  * We are making the OpenFlow specification and associated documentation
@@ -36,10 +36,7 @@
 #include <stddef.h>
 #include <stdint.h>
 
-#define HASH_FNV_BASIS UINT32_C(2166136261)
-#define HASH_FNV_PRIME UINT32_C(16777619)
-
-uint32_t hash_fnv(const void *, size_t, uint32_t basis);
-uint32_t hash_lookup3(const uint32_t *, size_t n, uint32_t basis);
+uint32_t hash_words(const uint32_t *, size_t n_word, uint32_t basis);
+uint32_t hash_bytes(const void *, size_t n_bytes, uint32_t basis);
 
 #endif /* hash.h */
diff --git a/lib/mac-learning.c b/lib/mac-learning.c
index 61c6fccb..aa1e3ad0 100644
--- a/lib/mac-learning.c
+++ b/lib/mac-learning.c
@@ -1,4 +1,4 @@
-/* Copyright (c) 2008 The Board of Trustees of The Leland Stanford
+/* Copyright (c) 2008, 2009 The Board of Trustees of The Leland Stanford
  * Junior University
  *
  * We are making the OpenFlow specification and associated documentation
@@ -79,7 +79,7 @@ struct mac_learning {
 static uint32_t
 mac_table_hash(const uint8_t mac[ETH_ADDR_LEN], uint16_t vlan)
 {
-    return hash_fnv(mac, ETH_ADDR_LEN, HASH_FNV_BASIS) ^ vlan;
+    return hash_bytes(mac, ETH_ADDR_LEN, vlan);
 }
 
 static struct mac_entry *
@@ -95,8 +95,9 @@ static tag_type
 make_unknown_mac_tag(const struct mac_learning *ml,
                      const uint8_t mac[ETH_ADDR_LEN], uint16_t vlan)
 {
-    return tag_create_deterministic(hash_fnv(&ml->secret, sizeof ml->secret,
-                                             mac_table_hash(mac, vlan)));
+    uint32_t h = hash_bytes(&ml->secret, sizeof ml->secret,
+                            mac_table_hash(mac, vlan));
+    return tag_create_deterministic(h);
 }
 
 static struct list *
diff --git a/lib/tag.c b/lib/tag.c
index ed198fcb..11d4dbe7 100644
--- a/lib/tag.c
+++ b/lib/tag.c
@@ -1,4 +1,4 @@
-/* Copyright (c) 2008 The Board of Trustees of The Leland Stanford
+/* Copyright (c) 2008, 2009 The Board of Trustees of The Leland Stanford
  * Junior University
  *
  * We are making the OpenFlow specification and associated documentation
@@ -61,7 +61,7 @@ tag_create_random(void)
  *
  * 'seed' should have data in all of its bits; if it has data only in its
  * low-order bits then the resulting tags will be poorly distributed.  Use a
- * hash function such as hash_lookup3() to generate 'seed' if necessary. */
+ * hash function such as hash_bytes() to generate 'seed' if necessary. */
 tag_type
 tag_create_deterministic(uint32_t seed)
 {
diff --git a/tests/test-hmap.c b/tests/test-hmap.c
index ee3289d1..962389fa 100644
--- a/tests/test-hmap.c
+++ b/tests/test-hmap.c
@@ -138,7 +138,7 @@ static size_t
 good_hash(int value)
 {
     const uint32_t x = value;
-    return hash_lookup3(&x, 1, 0x1234abcd);
+    return hash_words(&x, 1, 0x1234abcd);
 }
 
 static size_t
diff --git a/vswitchd/bridge.c b/vswitchd/bridge.c
index 9b88fcd4..4b8a343a 100644
--- a/vswitchd/bridge.c
+++ b/vswitchd/bridge.c
@@ -1174,7 +1174,7 @@ queue_tx(struct bridge *br, struct ofpbuf *msg)
 static struct bond_entry *
 lookup_bond_entry(const struct port *port, const uint8_t mac[ETH_ADDR_LEN])
 {
-    size_t h = hash_fnv(mac, ETH_ADDR_LEN, HASH_FNV_BASIS);
+    size_t h = hash_bytes(mac, ETH_ADDR_LEN, 0);
     return &port->bond_hash[h & BOND_MASK];
 }