Julian Day

从项目webalizer抓取到一个有用的关于儒略日(Julian Day)的函数。

关于"儒略日数"介绍参考

http://blog.sina.com.cn/s/blog_53027c620100mtii.html

/*****************************************************************/
/**/
/* JDATE  - Julian date calculator                               */
/**/
/* Calculates the number of days since Jan 1, 0000.              */
/**/
/* Originally written by Bradford L. Barrett (03/17/1988)        */
/* Returns an unsigned long value representing the number of     */
/* days since January 1, 0000.                                   */
/**/
/* Note: Due to the changes made by Pope Gregory XIII in the     */
/*       16th Centyry (Feb 24, 1582), dates before 1583 will     */
/*       not return a truely accurate number (will be at least   */
/*       10 days off).  Somehow, I don't think this will         */
/*       present much of a problem for most situations :)        */
/**/
/* Usage: days = jdate(day, month, year)                         */
/**/
/* The number returned is adjusted by 5 to facilitate day of     */
/* week calculations.  The mod of the returned value gives the   */
/* day of the week the date is.  (ie: dow = days % 7 ) where     */
/* dow will return 0=Sunday, 1=Monday, 2=Tuesday, etc...         */
/**/
/*****************************************************************/

u_int64_t jdate( int day, int month, int year )
{
   u_int64_t days;                      /* value returned */
   int mtable[] = {0,31,59,90,120,151,181,212,243,273,304,334};

   /* First, calculate base number including leap and Centenial year stuff */

   days=(((u_int64_t)year*365)+day+mtable[month-1]+
           ((year+4)/4) - ((year/100)-(year/400)));

   /* now adjust for leap year before March 1st */

   if ((year % 4 == 0) && !((year % 100 == 0) &&
       (year % 400 != 0)) && (month < 3))
   --days;

   /* done, return with calculated value */

   return(days+5);
}

如果调用得多的话，数组mtable声明为static是否要好些呢。