time31/bob hash methos

simple_hash.c

#include <stdint.h>

uint32_t time31_hash_bin(const void* data, uint32_t length)
{
    uint32_t hash = 0;
    const uint8_t* p = (const uint8_t*)data;
    const uint8_t* pend = p + length;
    for(; p < pend; ++p)
        hash = (hash<<5) - hash + *p;
    return hash;
}

uint32_t bob_hash_bin(const void* data, uint32_t length)
{
#define mix(a,b,c) \
a -= b; a -= c; a ^= (c >> 13);\
b -= c; b -= a; b ^= (a << 8);\
c -= a; c -= b; c ^= (b >> 13);\
a -= b; a -= c; a ^= (c >> 12);\
b -= c; b -= a; b ^= (a << 16);\
c -= a; c -= b; c ^= (b >> 5);\
a -= b; a -= c; a ^= (c >> 3);\
b -= c; b -= a; b ^= (a << 10);\
c -= a; c -= b; c ^= (b >> 15); 

    const uint8_t* k = (const uint8_t *)data;
    uint32_t a, b, c, len;

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

    /* Handle most of the key */
    while (len >= 12)
    {
        a += (k[0] +((uint32_t)k[1] << 8) +((uint32_t)k[2] << 16) +((uint32_t)k[3] << 24));
        b += (k[4] +((uint32_t)k[5] << 8) +((uint32_t)k[6] << 16) +((uint32_t)k[7] << 24));
        c += (k[8] +((uint32_t)k[9] << 8) +((uint32_t)k[10]<< 16)+((uint32_t)k[11] << 24));
        mix(a,b,c);
        k += 12; len -= 12;
    }

    /* Handle the last 11 bytes */
    c += length;
    switch(len)/* all the case statements fall through */
    {
    case 11: c+=((uint32_t)k[10] << 24);
    case 10: c+=((uint32_t)k[9]  << 16);
    case 9 : c+=((uint32_t)k[8]  << 8);
    /* the first byte of c is reserved for the length */
    case 8 : b+=((uint32_t)k[7] << 24);
    case 7 : b+=((uint32_t)k[6] << 16);
    case 6 : b+=((uint32_t)k[5] << 8);
    case 5 : b+=k[4];
    case 4 : a+=((uint32_t)k[3] << 24);
    case 3 : a+=((uint32_t)k[2] << 16);
    case 2 : a+=((uint32_t)k[1] << 8);
    case 1 : a+=k[0];
    }
    mix(a,b,c);

#undef mix

    return c;
}

uint64_t time31_bob_mixed_hash_bin(const void* data, uint32_t length)
{
    uint64_t time31_hash_val = time31_hash_bin(data, length);
    uint64_t bob_hash_value = bob_hash_bin(data, length);
    return (bob_hash_value<<32) | time31_hash_val;
}