squall/storm/string/bjhash.cpp

#include "storm/string/bjhash.hpp"

#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); \
    }

uint32_t bjhash(uint8_t* k, uint32_t length, uint32_t initval) {
    uint32_t a, b, c, len;

    len = length;       // Set up the internal state
    a = b = 0x9e3779b9; // The golden ratio; an arbitrary value
    c = initval;        // The previous hash 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);
    case 8:
        // The first byte of c is reserved for the length
        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];
    case 0:;
        // Nothing left to add
    }
    mix(a, b, c);

    // Report the result
    return c;
}