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 * https://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) {
  51        case 11:
  52                c = c + ((__u32)k[10] << 24);
  53                fallthrough;
  54        case 10:
  55                c = c + ((__u32)k[9] << 16);
  56                fallthrough;
  57        case 9:
  58                c = c + ((__u32)k[8] << 8);
  59                /* the first byte of c is reserved for the length */
  60                fallthrough;
  61        case 8:
  62                b = b + ((__u32)k[7] << 24);
  63                fallthrough;
  64        case 7:
  65                b = b + ((__u32)k[6] << 16);
  66                fallthrough;
  67        case 6:
  68                b = b + ((__u32)k[5] << 8);
  69                fallthrough;
  70        case 5:
  71                b = b + k[4];
  72                fallthrough;
  73        case 4:
  74                a = a + ((__u32)k[3] << 24);
  75                fallthrough;
  76        case 3:
  77                a = a + ((__u32)k[2] << 16);
  78                fallthrough;
  79        case 2:
  80                a = a + ((__u32)k[1] << 8);
  81                fallthrough;
  82        case 1:
  83                a = a + k[0];
  84                /* case 0: nothing left to add */
  85        }
  86        mix(a, b, c);
  87
  88        return c;
  89}
  90
  91/*
  92 * linux dcache hash
  93 */
  94unsigned int ceph_str_hash_linux(const char *str, unsigned int length)
  95{
  96        unsigned long hash = 0;
  97        unsigned char c;
  98
  99        while (length--) {
 100                c = *str++;
 101                hash = (hash + (c << 4) + (c >> 4)) * 11;
 102        }
 103        return hash;
 104}
 105
 106
 107unsigned int ceph_str_hash(int type, const char *s, unsigned int len)
 108{
 109        switch (type) {
 110        case CEPH_STR_HASH_LINUX:
 111                return ceph_str_hash_linux(s, len);
 112        case CEPH_STR_HASH_RJENKINS:
 113                return ceph_str_hash_rjenkins(s, len);
 114        default:
 115                return -1;
 116        }
 117}
 118EXPORT_SYMBOL(ceph_str_hash);
 119
 120const char *ceph_str_hash_name(int type)
 121{
 122        switch (type) {
 123        case CEPH_STR_HASH_LINUX:
 124                return "linux";
 125        case CEPH_STR_HASH_RJENKINS:
 126                return "rjenkins";
 127        default:
 128                return "unknown";
 129        }
 130}
 131EXPORT_SYMBOL(ceph_str_hash_name);
 132