MySQL hamming_distance

hamming_distance.c

#include <string.h>
#include <mysql.h>

my_bool hamming_distance_init(initid, args, message)
    UDF_INIT *initid;
    UDF_ARGS *args;
    char *message;
{
    if (args->arg_count != 2) {
        strcpy( message, "Wrong number of arguments to HAMMING_DISTANCE; accepts exactly two arguments." );
        return 1;
    }

    if ((args->arg_type[0] != STRING_RESULT) || (args->arg_type[1] != STRING_RESULT)) {
        strcpy( message, "One or both arguments to HAMMING_DISTANCE is not an string." );
        return 1;
    }

    return 0;
}

void hamming_distance_deinit(initid)
    UDF_INIT *initid;
{
    return;
}

long long hamming_distance(initid, args, is_null, error)
    UDF_INIT *initid;
    UDF_ARGS *args;
    char *is_null;
    char *error;
{
    if ((args->args[0] == NULL) || (args->args[1] == NULL)) {
        *error = 1;
        return 0;
    }

    if (args->lengths[0] != args->lengths[1]) {
        *error = 1;
        return 0;
    }

    if ((args->lengths[0] % 8) != 0) {
        *error = 1;
        return 0;
    }

    long long count = 0ll;
    int i, j;
    long long *v1 = (long long *)args->args[0];
    long long *v2 = (long long *)args->args[1];

    for(i = 0; i < (int)(args->lengths[0] / 8); i++) {
        count += __builtin_popcountll(v1[i] ^ v2[i]);
    }

    return count;
}