mktime.c ( File view )

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			/*
* linux/kernel/mktime.c
*
* (C) 1991 Linus Torvalds
*/

#include <time.h>		// 时间头文件,定义了标准时间数据结构tm 和一些处理时间函数原型。

/*
* This isn't the library routine, it is only used in the kernel.
* as such, we don't care about years<1970 etc, but assume everything
* is ok. Similarly, TZ etc is happily ignored. We just do everything
* as easily as possible. Let's find something public for the library
* routines (although I think minix times is public).
*/
/*
* PS. I hate whoever though up the year 1970 - couldn't they have gotten
* a leap-year instead? I also hate Gregorius, pope or no. I'm grumpy.
 */
/*
 * 这不是库函数,它仅供内核使用。因此我们不关心小于1970 年的年份等,但假定一切均很正常。
 * 同样,时间区域TZ 问题也先忽略。我们只是尽可能简单地处理问题。最好能找到一些公开的库函数
 * (尽管我认为minix 的时间函数是公开的)。
 * 另外,我恨那个设置1970 年开始的人 - 难道他们就不能选择从一个闰年开始?我恨格里高利历、
 * 罗马教皇、主教,我什么都不在乎。我是个脾气暴躁的人。
 */
#define MINUTE 60		// 1 分钟的秒数。
#define HOUR (60*MINUTE)	// 1 小时的秒数。
#define DAY (24*HOUR)		// 1 天的秒数。
#define YEAR (365*DAY)		// 1 年的秒数。

/* interestingly, we assume leap-years */
/* 有趣的是我们考虑进了闰年 */
// 下面以年为界限,定义了每个月开始时的秒数时间数组。
static int month[12] = {

  0,
  DAY * (31),
  DAY * (31 + 29),
  DAY * (31 + 29 + 31),
  DAY * (31 + 29 + 31 + 30),
  DAY * (31 + 29 + 31 + 30 + 31),
  DAY * (31 + 29 + 31 + 30 + 31 + 30),
  DAY * (31 + 29 + 31 + 30 + 31 + 30 + 31),
  DAY * (31 + 29 + 31 + 30 + 31 + 30 + 31 + 31),
  DAY * (31 + 29 + 31 + 30 + 31 + 30 + 31 + 31 + 30),
  DAY * (31 + 29 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31),
  DAY * (31 + 29 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30)

};

// 该函数计算从1970 年1 月1 日0 时起到开机当日经过的秒数,作为开机时间。
long
kernel_mktime (struct tm *tm)
{

  long res;
  int year;

  year = tm->tm_year - 70;	// 从70 年到现在经过的年数(2 位表示方式),
  // 因此会有2000 年问题。
  /* magic offsets (y+1) needed to get leapyears right. */
  /* 为了获得正确的闰年数,这里需要这样一个魔幻偏值(y+1) */
  res = YEAR * year + DAY * ((year + 1) / 4);	// 这些年经过的秒数时间 + 每个闰年时多1 天
  res += month[tm->tm_mon];	// 的秒数时间,在加上当年到当月时的秒数。
  /* and (y+2) here. If it wasn't a leap-year, we have to adjust */
  /* 以及(y+2)。如果(y+2)不是闰年,那么我们就必须进行调整(减去一天的秒数时间)。 */
  if (tm->tm_mon > 1 && ((year + 2) % 4))
    res -= DAY;
  res += DAY * (tm->tm_mday - 1);	// 再加上本月过去的天数的秒数时间。
  res += HOUR * tm->tm_hour;	// 再加上当天过去的小时数的秒数时间。
  res += MINUTE * tm->tm_min;	// 再加上1 小时内过去的分钟数的秒数时间。
  res += tm->tm_sec;		// 再加上1 分钟内已过的秒数。
  return res;			// 即等于从1970 年以来经过的秒数时间。

}
			
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Makefile3.21 kB08-01-04 23:01
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mktime.c2.72 kB02-09-04 13:12
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