#include "stddef.h"
#include <errno.h>
#include <stdlib.h>
#include <time.h>
#include <stdio.h>

const char *wday_str[7]={"Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"};
const char *mon_str[12]={"Jan", "Feb", "Mar", "Ap", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"};

#pragma GCC push_options
#pragma GCC optimize("O0")

#define TIME_STR_MAX 27

char *asctime(const struct tm *tm){
    if(!tm){
        errno = EINVAL;
        return NULL;
    }
    if(tm->tm_wday>6 || tm->tm_wday<0 || tm->tm_mon<0 || tm->tm_mon>11){
        errno = EINVAL;
        return NULL;
    }
    static char time_str[TIME_STR_MAX];
    snprintf(time_str, TIME_STR_MAX-1, "%.3s %.3s%3d %02d:%02d:%02d %d\n",
        wday_str[tm->tm_wday],
        mon_str[tm->tm_mon],
        tm->tm_mday, tm->tm_hour,
        tm->tm_min, tm->tm_sec,
        1900 + tm->tm_year
    );
    return time_str;
}
#pragma GCC pop_options