mysql 自定义哈希函数

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

// 自定义哈希函数
unsigned int my_hash_func(UDF_INIT *initid, UDF_ARGS *args, char *is_null, char *error) {
    unsigned long *length = args->lengths;
    char *src = (char *)args->args[0];
    unsigned int hash = 5381;
    int c;

    for (size_t i = 0; i < *length; i++) {
        c = src[i];
        hash = ((hash << 5) + hash) + c; /* hash * 33 + c */
    }

    return hash;
}

// UDF初始化
my_bool my_hash_init(UDF_INIT *initid, UDF_ARGS *args, char *message) {
    if (args->arg_count != 1 || args->arg_type[0] != REAL_RESULT) {
        strcpy(message, "Hash function requires one argument of type REAL_RESULT");
        return 1;
    }
    return 0;
}

// UDF去初始化
void my_hash_deinit(UDF_INIT *initid) {
    // 清理资源
}

// 注册UDF
mysql_declare_plugin(my_hash){
    MYSQL_UDF_HASH,
    "my_hash",
    my_hash_func,
    my_hash_init,
    my_hash_deinit,
    0x0100,
    "GPL",
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL
}
mysql_declare_plugin_end;