获取某个时间的当前毫秒数（相对于格林时间）

typedef unsigned char BYTE;
typedef unsigned short WORD;

typedef struct
{
 WORD wYear;
 BYTE byMonth;
 BYTE byDay;
 BYTE byHour;
 BYTE byMinute;
 BYTE bySecond;
 WORD wMilliSec;
}SDateTime;
#define TM_YEAR_BASE 0


#define isleap(y) ((((y) % 4) == 0 && ((y) % 100) != 0 ) || (((y) % 400) == 0 && ((y) % 4000) != 0))

/************************************************************************
*
*  daysSinceEpoch - calculate number days since ANSI C epoch                 
* 
*  The (year + 1)/4 term accounts for leap years, the     
*  first of which was 1972 & should be added starting ‘73 
* 
* RETURNS:
* NOMANUAL
*/
int __daysSinceEpoch_db( int year, /* Years since epoch */int yday  /* days since Jan 1  */)
{
 if( year >= 0 ) /* 1970 + */
     return ( (365 * year) + (year + 1) / 4  + yday );
 else  /* 1969 - */
     return ( (365 * year) + (year - 2) / 4  + yday );
}

/************************************************************************
*
* julday - calculate Julian Day given year, month, day            
*              Inputs      : year (years since 1900), month (0 - 11), 
*             day (1 - 31)  
*              Comment     : Returns Julian day in range 1:366.  
*        Unix wants 0:365 
* RETURNS: Julian day                                            
* NOMANUAL
*/
int __julday_db( int yr, /* year */int mon, /* month */int day /* day */)
{
    static jdays[12] = {0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334};
    int leap = 0;
    if (isleap (yr + TM_YEAR_BASE))
	{
	 /*
	  * If it is a leap year, leap only gets set if the day is
	  * after beginning of March (SPR #4251).
	  */
	 if (mon > 1)
		 leap = 1;
	}
    return (jdays[mon] + day + leap);
}
    
/**********************************************************************
    GetSecondSinceEpoch--Get Seconds since 1970
*/
int GetSecondSinceEpoch(SDateTime* sDateTime)
{
    int julday;
    int day;

	if( sDateTime->wYear < 100 )
	{
	   sDateTime->wYear += 2000 ;
	}/*if*/
    julday=__julday_db(sDateTime->wYear,sDateTime->byMonth - 1,sDateTime->byDay );
    
	day=__daysSinceEpoch_db(sDateTime->wYear-1970,julday);
    return( ( (day*24 + sDateTime->byHour)*60 + sDateTime->byMinute )*60 +sDateTime->bySecond);
}