ceph_hash.c

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#include <linux/ceph/types.h>
#include <linux/module.h>

/*
 * Robert Jenkin's hash function.
 * http://burtleburtle.net/bob/hash/evahash.html
 * This is in the public domain.
 */
#define mix(a, b, c)                        \
    do {                            \
        a = a - b;  a = a - c;  a = a ^ (c >> 13);  \
        b = b - c;  b = b - a;  b = b ^ (a << 8);   \
        c = c - a;  c = c - b;  c = c ^ (b >> 13);  \
        a = a - b;  a = a - c;  a = a ^ (c >> 12);  \
        b = b - c;  b = b - a;  b = b ^ (a << 16);  \
        c = c - a;  c = c - b;  c = c ^ (b >> 5);   \
        a = a - b;  a = a - c;  a = a ^ (c >> 3);   \
        b = b - c;  b = b - a;  b = b ^ (a << 10);  \
        c = c - a;  c = c - b;  c = c ^ (b >> 15);  \
    } while (0)

unsigned int ceph_str_hash_rjenkins(const char *str, unsigned int length)
{
    const unsigned char *k = (const unsigned char *)str;
    __u32 a, b, c;  /* the internal state */
    __u32 len;      /* how many key bytes still need mixing */

    /* Set up the internal state */
    len = length;
    a = 0x9e3779b9;      /* the golden ratio; an arbitrary value */
    b = a;
    c = 0;               /* variable initialization of internal state */

    /* handle most of the key */
    while (len >= 12) {
        a = a + (k[0] + ((__u32)k[1] << 8) + ((__u32)k[2] << 16) +
             ((__u32)k[3] << 24));
        b = b + (k[4] + ((__u32)k[5] << 8) + ((__u32)k[6] << 16) +
             ((__u32)k[7] << 24));
        c = c + (k[8] + ((__u32)k[9] << 8) + ((__u32)k[10] << 16) +
             ((__u32)k[11] << 24));
        mix(a, b, c);
        k = k + 12;
        len = len - 12;
    }

    /* handle the last 11 bytes */
    c = c + length;
    switch (len) {            /* all the case statements fall through */
    case 11:
        c = c + ((__u32)k[10] << 24);
    case 10:
        c = c + ((__u32)k[9] << 16);
    case 9:
        c = c + ((__u32)k[8] << 8);
        /* the first byte of c is reserved for the length */
    case 8:
        b = b + ((__u32)k[7] << 24);
    case 7:
        b = b + ((__u32)k[6] << 16);
    case 6:
        b = b + ((__u32)k[5] << 8);
    case 5:
        b = b + k[4];
    case 4:
        a = a + ((__u32)k[3] << 24);
    case 3:
        a = a + ((__u32)k[2] << 16);
    case 2:
        a = a + ((__u32)k[1] << 8);
    case 1:
        a = a + k[0];
        /* case 0: nothing left to add */
    }
    mix(a, b, c);

    return c;
}

/*
 * linux dcache hash
 */
unsigned int ceph_str_hash_linux(const char *str, unsigned int length)
{
    unsigned long hash = 0;
    unsigned char c;

    while (length--) {
        c = *str++;
        hash = (hash + (c << 4) + (c >> 4)) * 11;
    }
    return hash;
}


unsigned int ceph_str_hash(int type, const char *s, unsigned int len)
{
    switch (type) {
    case CEPH_STR_HASH_LINUX:
        return ceph_str_hash_linux(s, len);
    case CEPH_STR_HASH_RJENKINS:
        return ceph_str_hash_rjenkins(s, len);
    default:
        return -1;
    }
}
EXPORT_SYMBOL(ceph_str_hash);

const char *ceph_str_hash_name(int type)
{
    switch (type) {
    case CEPH_STR_HASH_LINUX:
        return "linux";
    case CEPH_STR_HASH_RJENKINS:
        return "rjenkins";
    default:
        return "unknown";
    }
}
EXPORT_SYMBOL(ceph_str_hash_name);