fs/ceph/ceph_hash.c

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