LXR linux/net/ceph/ceph

   1
   2#include <linux/ceph/types.h>
   3#include <linux/module.h>
   4
   5/*
   6 * Robert Jenkin's hash function.
   7 * http://burtleburtle.net/bob/hash/evahash.html
   8 * This is in the public domain.
   9 */
  10#define mix(a, b, c)                                            \
  11        do {                                                    \
  12                a = a - b;  a = a - c;  a = a ^ (c >> 13);      \
  13                b = b - c;  b = b - a;  b = b ^ (a << 8);       \
  14                c = c - a;  c = c - b;  c = c ^ (b >> 13);      \
  15                a = a - b;  a = a - c;  a = a ^ (c >> 12);      \
  16                b = b - c;  b = b - a;  b = b ^ (a << 16);      \
  17                c = c - a;  c = c - b;  c = c ^ (b >> 5);       \
  18                a = a - b;  a = a - c;  a = a ^ (c >> 3);       \
  19                b = b - c;  b = b - a;  b = b ^ (a << 10);      \
  20                c = c - a;  c = c - b;  c = c ^ (b >> 15);      \
  21        } while (0)
  22
  23unsigned int ceph_str_hash_rjenkins(const char *str, unsigned int length)
  24{
  25        const unsigned char *k = (const unsigned char *)str;
  26        __u32 a, b, c;  /* the internal state */
  27        __u32 len;      /* how many key bytes still need mixing */
  28
  29        /* Set up the internal state */
  30        len = length;
  31        a = 0x9e3779b9;      /* the golden ratio; an arbitrary value */
  32        b = a;
  33        c = 0;               /* variable initialization of internal state */
  34
  35        /* handle most of the key */
  36        while (len >= 12) {
  37                a = a + (k[0] + ((__u32)k[1] << 8) + ((__u32)k[2] << 16) +
  38                         ((__u32)k[3] << 24));
  39                b = b + (k[4] + ((__u32)k[5] << 8) + ((__u32)k[6] << 16) +
  40                         ((__u32)k[7] << 24));
  41                c = c + (k[8] + ((__u32)k[9] << 8) + ((__u32)k[10] << 16) +
  42                         ((__u32)k[11] << 24));
  43                mix(a, b, c);
  44                k = k + 12;
  45                len = len - 12;
  46        }
  47
  48        /* handle the last 11 bytes */
  49        c = c + length;
  50        switch (len) {            /* all the case statements fall through */
  51        case 11:
  52                c = c + ((__u32)k[10] << 24);
  53        case 10:
  54                c = c + ((__u32)k[9] << 16);
  55        case 9:
  56                c = c + ((__u32)k[8] << 8);
  57                /* the first byte of c is reserved for the length */
  58        case 8:
  59                b = b + ((__u32)k[7] << 24);
  60        case 7:
  61                b = b + ((__u32)k[6] << 16);
  62        case 6:
  63                b = b + ((__u32)k[5] << 8);
  64        case 5:
  65                b = b + k[4];
  66        case 4:
  67                a = a + ((__u32)k[3] << 24);
  68        case 3:
  69                a = a + ((__u32)k[2] << 16);
  70        case 2:
  71                a = a + ((__u32)k[1] << 8);
  72        case 1:
  73                a = a + k[0];
  74                /* case 0: nothing left to add */
  75        }
  76        mix(a, b, c);
  77
  78        return c;
  79}
  80
  81/*
  82 * linux dcache hash
  83 */
  84unsigned int ceph_str_hash_linux(const char *str, unsigned int length)
  85{
  86        unsigned long hash = 0;
  87        unsigned char c;
  88
  89        while (length--) {
  90                c = *str++;
  91                hash = (hash + (c << 4) + (c >> 4)) * 11;
  92        }
  93        return hash;
  94}
  95
  96
  97unsigned int ceph_str_hash(int type, const char *s, unsigned int len)
  98{
  99        switch (type) {
 100        case CEPH_STR_HASH_LINUX:
 101                return ceph_str_hash_linux(s, len);
 102        case CEPH_STR_HASH_RJENKINS:
 103                return ceph_str_hash_rjenkins(s, len);
 104        default:
 105                return -1;
 106        }
 107}
 108EXPORT_SYMBOL(ceph_str_hash);
 109
 110const char *ceph_str_hash_name(int type)
 111{
 112        switch (type) {
 113        case CEPH_STR_HASH_LINUX:
 114                return "linux";
 115        case CEPH_STR_HASH_RJENKINS:
 116                return "rjenkins";
 117        default:
 118                return "unknown";
 119        }
 120}
 121EXPORT_SYMBOL(ceph_str_hash_name);
 122