mktime代码的实现

#include <stdio.h>
/*
    计算从
*/
unsigned long My_mktime(unsigned int year, unsigned int mon, unsigned int day,
                                unsigned int hour, unsigned int min, unsigned int second)
{
    unsigned int year_to_day = 0;
    unsigned int mon_to_day = 0;
    unsigned int day_to_day = 0;
    /*把1月和2月当作上一年年底的最后两个月，让3月作为一年的第一个月*/
    if((mon -= 2) <= 0)
    {
        mon += 12;
        year -= 1;
    }

    year_to_day = (year - 1) * 365 + year / 4 - year / 100 + year / 400; //计算给出的年数到公元元年的天数
    mon_to_day = (367 * mon / 12) - 30 + 59; //计算给出的月数转换成天数
    day_to_day = day - 1; //当天不能计算上去，所以要减1
    /*719162是0001年1月1日到1970年1月1日所经历的天数*/
    return (((unsigned long)(((year_to_day + mon_to_day + day_to_day - 719162) * 24 + hour) * 60 + min) * 60) + second);
}


typedef struct{
    unsigned char tm_sec;//00～59
    unsigned char tm_min;//00～59
    unsigned char tm_hour;//00～23
    unsigned char tm_mday;//01～31
    unsigned char tm_mon;//01～12
    unsigned char tm_year;//00～99
    unsigned char tm_week;//00～06  设置rtc时间时，不需要设置tm_week选项，获取rtc时间 时，可以得到一个准确的tm_week值
}date_time_t;

unsigned long Dt_mktime_abs(date_time_t *pTm)
{
    int year/*[2000, 2099]*/ = pTm->tm_year/*[00, 99]*/ + 2000;
    int mon/*[1, 12]*/ = pTm->tm_mon/*[1, 12]*/;
    int day/*[1, 31]*/ = pTm->tm_mday/*[1, 31]*/;
    int hour = pTm->tm_hour/*[0, 23]*/;
    int min = pTm->tm_min/*[0, 59]*/;
    int sec = pTm->tm_sec/*[0, 59]*/;

    /**/
    if(((int)(mon -= 2)) <= 0)
    {
        mon += 12;/* Puts Feb last since it has leap day */
        year -= 1;
    }

    return ((((unsigned long)(year / 4 - year / 100 + year / 400 + 367 * mon / 12 + day) + year * 365 - 719499) * 24
                    + hour /* now have hours */) * 60 + min /* now have minutes */)*60 + sec; /* finally seconds */
}


int main(int argc, char **argv)
{
    unsigned long time1 = 0;
    unsigned long time2 = 0;
    date_time_t time;

    time.tm_year = 17;
    time.tm_mon = 5;
    time.tm_mday = 16;
    time.tm_hour = 9;
    time.tm_min = 9;
    time.tm_sec = 9;

    /**/
    time1 = Dt_mktime_abs(&time);
    time2 = My_mktime(2017, 5, 16, 9, 9, 9);

    printf("time1:%ld,time2:%ld\n", time1, time2);

    return 0;
}