net/ceph/ceph_hash.c

0001
0002 #include <linux/ceph/types.h>
0003 #include <linux/module.h>
0004
0005 /*
0006  * Robert Jenkin's hash function.
0007  * https://burtleburtle.net/bob/hash/evahash.html
0008  * This is in the public domain.
0009  */
0010 #define mix(a, b, c)                        \
0011     do {                            \
0012         a = a - b;  a = a - c;  a = a ^ (c >> 13);  \
0013         b = b - c;  b = b - a;  b = b ^ (a << 8);   \
0014         c = c - a;  c = c - b;  c = c ^ (b >> 13);  \
0015         a = a - b;  a = a - c;  a = a ^ (c >> 12);  \
0016         b = b - c;  b = b - a;  b = b ^ (a << 16);  \
0017         c = c - a;  c = c - b;  c = c ^ (b >> 5);   \
0018         a = a - b;  a = a - c;  a = a ^ (c >> 3);   \
0019         b = b - c;  b = b - a;  b = b ^ (a << 10);  \
0020         c = c - a;  c = c - b;  c = c ^ (b >> 15);  \
0021     } while (0)
0022
0023 unsigned int ceph_str_hash_rjenkins(const char *str, unsigned int length)
0024 {
0025     const unsigned char *k = (const unsigned char *)str;
0026     __u32 a, b, c;  /* the internal state */
0027     __u32 len;      /* how many key bytes still need mixing */
0028
0029     /* Set up the internal state */
0030     len = length;
0031     a = 0x9e3779b9;      /* the golden ratio; an arbitrary value */
0032     b = a;
0033     c = 0;               /* variable initialization of internal state */
0034
0035     /* handle most of the key */
0036     while (len >= 12) {
0037         a = a + (k[0] + ((__u32)k[1] << 8) + ((__u32)k[2] << 16) +
0038              ((__u32)k[3] << 24));
0039         b = b + (k[4] + ((__u32)k[5] << 8) + ((__u32)k[6] << 16) +
0040              ((__u32)k[7] << 24));
0041         c = c + (k[8] + ((__u32)k[9] << 8) + ((__u32)k[10] << 16) +
0042              ((__u32)k[11] << 24));
0043         mix(a, b, c);
0044         k = k + 12;
0045         len = len - 12;
0046     }
0047
0048     /* handle the last 11 bytes */
0049     c = c + length;
0050     switch (len) {
0051     case 11:
0052         c = c + ((__u32)k[10] << 24);
0053         fallthrough;
0054     case 10:
0055         c = c + ((__u32)k[9] << 16);
0056         fallthrough;
0057     case 9:
0058         c = c + ((__u32)k[8] << 8);
0059         /* the first byte of c is reserved for the length */
0060         fallthrough;
0061     case 8:
0062         b = b + ((__u32)k[7] << 24);
0063         fallthrough;
0064     case 7:
0065         b = b + ((__u32)k[6] << 16);
0066         fallthrough;
0067     case 6:
0068         b = b + ((__u32)k[5] << 8);
0069         fallthrough;
0070     case 5:
0071         b = b + k[4];
0072         fallthrough;
0073     case 4:
0074         a = a + ((__u32)k[3] << 24);
0075         fallthrough;
0076     case 3:
0077         a = a + ((__u32)k[2] << 16);
0078         fallthrough;
0079     case 2:
0080         a = a + ((__u32)k[1] << 8);
0081         fallthrough;
0082     case 1:
0083         a = a + k[0];
0084         /* case 0: nothing left to add */
0085     }
0086     mix(a, b, c);
0087
0088     return c;
0089 }
0090
0091 /*
0092  * linux dcache hash
0093  */
0094 unsigned int ceph_str_hash_linux(const char *str, unsigned int length)
0095 {
0096     unsigned long hash = 0;
0097     unsigned char c;
0098
0099     while (length--) {
0100         c = *str++;
0101         hash = (hash + (c << 4) + (c >> 4)) * 11;
0102     }
0103     return hash;
0104 }
0105
0106
0107 unsigned int ceph_str_hash(int type, const char *s, unsigned int len)
0108 {
0109     switch (type) {
0110     case CEPH_STR_HASH_LINUX:
0111         return ceph_str_hash_linux(s, len);
0112     case CEPH_STR_HASH_RJENKINS:
0113         return ceph_str_hash_rjenkins(s, len);
0114     default:
0115         return -1;
0116     }
0117 }
0118 EXPORT_SYMBOL(ceph_str_hash);
0119
0120 const char *ceph_str_hash_name(int type)
0121 {
0122     switch (type) {
0123     case CEPH_STR_HASH_LINUX:
0124         return "linux";
0125     case CEPH_STR_HASH_RJENKINS:
0126         return "rjenkins";
0127     default:
0128         return "unknown";
0129     }
0130 }
0131 EXPORT_SYMBOL(ceph_str_hash_name);