ceph_hash.c
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#include <linux/ceph/types.h>
#include <linux/module.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;
}
}
EXPORT_SYMBOL(ceph_str_hash);
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";
}
}
EXPORT_SYMBOL(ceph_str_hash_name);