include/linux/time.h

#ifndef _LINUX_TIME_H
#define _LINUX_TIME_H

#include <asm/param.h>
#include <linux/types.h>

#ifndef _STRUCT_TIMESPEC
#define _STRUCT_TIMESPEC
struct timespec {
	time_t	tv_sec;		/* seconds */
	long	tv_nsec;	/* nanoseconds */
};
#endif /* _STRUCT_TIMESPEC */

#ifdef __KERNEL__

/*
 * Change timeval to jiffies, trying to avoid the
 * most obvious overflows..
 *
 * And some not so obvious.
 *
 * Note that we don't want to return MAX_LONG, because
 * for various timeout reasons we often end up having
 * to wait "jiffies+1" in order to guarantee that we wait
 * at _least_ "jiffies" - so "jiffies+1" had better still
 * be positive.
 */
#define MAX_JIFFY_OFFSET ((~0UL >> 1)-1)

static __inline__ unsigned long
timespec_to_jiffies(struct timespec *value)
{
	unsigned long sec = value->tv_sec;
	long nsec = value->tv_nsec;

	if (sec >= (MAX_JIFFY_OFFSET / HZ))
		return MAX_JIFFY_OFFSET;
	nsec += 1000000000L / HZ - 1;
	nsec /= 1000000000L / HZ;
	return HZ * sec + nsec;
}

static __inline__ void
jiffies_to_timespec(unsigned long jiffies, struct timespec *value)
{
	value->tv_nsec = (jiffies % HZ) * (1000000000L / HZ);
	value->tv_sec = jiffies / HZ;
}


/* Converts Gregorian date to seconds since 1970-01-01 00:00:00.
 * Assumes input in normal date format, i.e. 1980-12-31 23:59:59
 * => year=1980, mon=12, day=31, hour=23, min=59, sec=59.
 *
 * [For the Julian calendar (which was used in Russia before 1917,
 * Britain & colonies before 1752, anywhere else before 1582,
 * and is still in use by some communities) leave out the
 * -year/100+year/400 terms, and add 10.]
 *
 * This algorithm was first published by Gauss (I think).
 *
 * WARNING: this function will overflow on 2106-02-07 06:28:16 on
 * machines were long is 32-bit! (However, as time_t is signed, we
 * will already get problems at other places on 2038-01-19 03:14:08)
 */
static inline unsigned long
mktime (unsigned int year, unsigned int mon,
	unsigned int day, unsigned int hour,
	unsigned int min, unsigned int sec)
{
	if (0 >= (int) (mon -= 2)) {	/* 1..12 -> 11,12,1..10 */
		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 */
}

#endif /* __KERNEL__ */


struct timeval {
	time_t		tv_sec;		/* seconds */
	suseconds_t	tv_usec;	/* microseconds */
};

struct timezone {
	int	tz_minuteswest;	/* minutes west of Greenwich */
	int	tz_dsttime;	/* type of dst correction */
};

#define NFDBITS			__NFDBITS

#ifdef __KERNEL__
extern void do_gettimeofday(struct timeval *tv);
extern void do_settimeofday(struct timeval *tv);
#endif

#define FD_SETSIZE		__FD_SETSIZE
#define FD_SET(fd,fdsetp)	__FD_SET(fd,fdsetp)
#define FD_CLR(fd,fdsetp)	__FD_CLR(fd,fdsetp)
#define FD_ISSET(fd,fdsetp)	__FD_ISSET(fd,fdsetp)
#define FD_ZERO(fdsetp)		__FD_ZERO(fdsetp)

/*
 * Names of the interval timers, and structure
 * defining a timer setting.
 */
#define	ITIMER_REAL	0
#define	ITIMER_VIRTUAL	1
#define	ITIMER_PROF	2

struct  itimerspec {
        struct  timespec it_interval;    /* timer period */
        struct  timespec it_value;       /* timer expiration */
};

struct	itimerval {
	struct	timeval it_interval;	/* timer interval */
	struct	timeval it_value;	/* current value */
};

#endif