net/ceph/ceph_hash.c

   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
  23 unsigned ceph_str_hash_rjenkins(const char *str, unsigned 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  */
  84 unsigned ceph_str_hash_linux(const char *str, unsigned 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
  97 unsigned ceph_str_hash(int type, const char *s, unsigned 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 }
 108 EXPORT_SYMBOL(ceph_str_hash);
 109
 110 const 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 }
 121 EXPORT_SYMBOL(ceph_str_hash_name);