jhash

Kernel version: 2.6.18
/include/linux/jhash.h

Code:

/* A special ultra-optimized versions that knows they are hashing exactly
 * 3, 2 or 1 word(s).
 *
 * NOTE: In partilar the "c += length; __jhash_mix(a,b,c);" normally
 *       done at the end is not done here.
 */
static inline u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval)
{
        a += JHASH_GOLDEN_RATIO;
        b += JHASH_GOLDEN_RATIO;
        c += initval;

        __jhash_mix(a, b, c);

        return c;
}

Usage:

/*
 *      Returns hash value for IPVS connection entry
 */
static unsigned int ip_vs_conn_hashkey(unsigned proto, __u32 addr, __u16 port)
{
        return jhash_3words(addr, port, proto, ip_vs_conn_rnd)
                & IP_VS_CONN_TAB_MASK;
}

ip_vs_conn_rnd:
 Initialize at ip_vs_conn_init(void).
 Randon value of static unsigned int.

IP_VS_CONN_TAB_MASK: (4098)
 Defined in ip_vs.h
#define CONFIG_IP_VS_TAB_BITS   12 //default
#define IP_VS_CONN_TAB_BITS     CONFIG_IP_VS_TAB_BITS
#define IP_VS_CONN_TAB_SIZE     (1 << IP_VS_CONN_TAB_BITS)
#define IP_VS_CONN_TAB_MASK     (IP_VS_CONN_TAB_SIZE - 1)