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

/*
 * Robert Jenkin's hash function.
 * https://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) {
        case 11:
                c = c + ((__u32)k[10] << 24);
                fallthrough;
        case 10:
                c = c + ((__u32)k[9] << 16);
                fallthrough;
        case 9:
                c = c + ((__u32)k[8] << 8);
                /* the first byte of c is reserved for the length */
                fallthrough;
        case 8:
                b = b + ((__u32)k[7] << 24);
                fallthrough;
        case 7:
                b = b + ((__u32)k[6] << 16);
                fallthrough;
        case 6:
                b = b + ((__u32)k[5] << 8);
                fallthrough;
        case 5:
                b = b + k[4];
                fallthrough;
        case 4:
                a = a + ((__u32)k[3] << 24);
                fallthrough;
        case 3:
                a = a + ((__u32)k[2] << 16);
                fallthrough;
        case 2:
                a = a + ((__u32)k[1] << 8);
                fallthrough;
        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);