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Date: Tue, 2 Mar 2010 16:46:35 -0800
From: Sage Weil <sage@...dream.net>
To: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: Sage Weil <sage@...dream.net>
Subject: [PATCH 04/26] ceph: hash function
Define the hash functions used for placing dentries in directories
and for mapping objects into placement groups.
Signed-off-by: Sage Weil <sage@...dream.net>
---
fs/ceph/ceph_hash.c | 118 +++++++++++++++++++++++++++++++++++++++++++++++++++
fs/ceph/ceph_hash.h | 13 ++++++
2 files changed, 131 insertions(+), 0 deletions(-)
create mode 100644 fs/ceph/ceph_hash.c
create mode 100644 fs/ceph/ceph_hash.h
diff --git a/fs/ceph/ceph_hash.c b/fs/ceph/ceph_hash.c
new file mode 100644
index 0000000..bd57001
--- /dev/null
+++ b/fs/ceph/ceph_hash.c
@@ -0,0 +1,118 @@
+
+#include "types.h"
+
+/*
+ * Robert Jenkin's hash function.
+ * http://burtleburtle.net/bob/hash/evahash.html
+ * This is in the public domain.
+ */
+#define mix(a, b, c) \
+ do { \
+ a = a - b; a = a - c; a = a ^ (c >> 13); \
+ b = b - c; b = b - a; b = b ^ (a << 8); \
+ c = c - a; c = c - b; c = c ^ (b >> 13); \
+ a = a - b; a = a - c; a = a ^ (c >> 12); \
+ b = b - c; b = b - a; b = b ^ (a << 16); \
+ c = c - a; c = c - b; c = c ^ (b >> 5); \
+ a = a - b; a = a - c; a = a ^ (c >> 3); \
+ b = b - c; b = b - a; b = b ^ (a << 10); \
+ c = c - a; c = c - b; c = c ^ (b >> 15); \
+ } while (0)
+
+unsigned ceph_str_hash_rjenkins(const char *str, unsigned length)
+{
+ const unsigned char *k = (const unsigned char *)str;
+ __u32 a, b, c; /* the internal state */
+ __u32 len; /* how many key bytes still need mixing */
+
+ /* Set up the internal state */
+ len = length;
+ a = 0x9e3779b9; /* the golden ratio; an arbitrary value */
+ b = a;
+ c = 0; /* variable initialization of internal state */
+
+ /* handle most of the key */
+ while (len >= 12) {
+ a = a + (k[0] + ((__u32)k[1] << 8) + ((__u32)k[2] << 16) +
+ ((__u32)k[3] << 24));
+ b = b + (k[4] + ((__u32)k[5] << 8) + ((__u32)k[6] << 16) +
+ ((__u32)k[7] << 24));
+ c = c + (k[8] + ((__u32)k[9] << 8) + ((__u32)k[10] << 16) +
+ ((__u32)k[11] << 24));
+ mix(a, b, c);
+ k = k + 12;
+ len = len - 12;
+ }
+
+ /* handle the last 11 bytes */
+ c = c + length;
+ switch (len) { /* all the case statements fall through */
+ case 11:
+ c = c + ((__u32)k[10] << 24);
+ case 10:
+ c = c + ((__u32)k[9] << 16);
+ case 9:
+ c = c + ((__u32)k[8] << 8);
+ /* the first byte of c is reserved for the length */
+ case 8:
+ b = b + ((__u32)k[7] << 24);
+ case 7:
+ b = b + ((__u32)k[6] << 16);
+ case 6:
+ b = b + ((__u32)k[5] << 8);
+ case 5:
+ b = b + k[4];
+ case 4:
+ a = a + ((__u32)k[3] << 24);
+ case 3:
+ a = a + ((__u32)k[2] << 16);
+ case 2:
+ a = a + ((__u32)k[1] << 8);
+ case 1:
+ a = a + k[0];
+ /* case 0: nothing left to add */
+ }
+ mix(a, b, c);
+
+ return c;
+}
+
+/*
+ * linux dcache hash
+ */
+unsigned ceph_str_hash_linux(const char *str, unsigned length)
+{
+ unsigned long hash = 0;
+ unsigned char c;
+
+ while (length--) {
+ c = *str++;
+ hash = (hash + (c << 4) + (c >> 4)) * 11;
+ }
+ return hash;
+}
+
+
+unsigned ceph_str_hash(int type, const char *s, unsigned len)
+{
+ switch (type) {
+ case CEPH_STR_HASH_LINUX:
+ return ceph_str_hash_linux(s, len);
+ case CEPH_STR_HASH_RJENKINS:
+ return ceph_str_hash_rjenkins(s, len);
+ default:
+ return -1;
+ }
+}
+
+const char *ceph_str_hash_name(int type)
+{
+ switch (type) {
+ case CEPH_STR_HASH_LINUX:
+ return "linux";
+ case CEPH_STR_HASH_RJENKINS:
+ return "rjenkins";
+ default:
+ return "unknown";
+ }
+}
diff --git a/fs/ceph/ceph_hash.h b/fs/ceph/ceph_hash.h
new file mode 100644
index 0000000..5ac470c
--- /dev/null
+++ b/fs/ceph/ceph_hash.h
@@ -0,0 +1,13 @@
+#ifndef _FS_CEPH_HASH_H
+#define _FS_CEPH_HASH_H
+
+#define CEPH_STR_HASH_LINUX 0x1 /* linux dcache hash */
+#define CEPH_STR_HASH_RJENKINS 0x2 /* robert jenkins' */
+
+extern unsigned ceph_str_hash_linux(const char *s, unsigned len);
+extern unsigned ceph_str_hash_rjenkins(const char *s, unsigned len);
+
+extern unsigned ceph_str_hash(int type, const char *s, unsigned len);
+extern const char *ceph_str_hash_name(int type);
+
+#endif
--
1.7.0
--
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