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/*

 * mktime.c

 * Original Author:     G. Haley

 *

 * Converts the broken-down time, expressed as local time, in the structure

 * pointed to by tim_p into a calendar time value. The original values of the

 * tm_wday and tm_yday fields of the structure are ignored, and the original

 * values of the other fields have no restrictions. On successful completion

 * the fields of the structure are set to represent the specified calendar

 * time. Returns the specified calendar time. If the calendar time can not be

 * represented, returns the value (time_t) -1.

 */

/*

FUNCTION

<<mktime>>---convert time to arithmetic representation

INDEX

        mktime

ANSI_SYNOPSIS

        #include <time.h>

        time_t mktime(struct tm *<[timp]>);

TRAD_SYNOPSIS

        #include <time.h>

        time_t mktime(<[timp]>)

        struct tm *<[timp]>;

DESCRIPTION

<<mktime>> assumes the time at <[timp]> is a local time, and converts

its representation from the traditional representation defined by

<<struct tm>> into a representation suitable for arithmetic.

<<localtime>> is the inverse of <<mktime>>.

RETURNS

If the contents of the structure at <[timp]> do not form a valid

calendar time representation, the result is <<-1>>.  Otherwise, the

result is the time, converted to a <<time_t>> value.

PORTABILITY

ANSI C requires <<mktime>>.

<<mktime>> requires no supporting OS subroutines.

*/

#include <stdlib.h>

#include <time.h>

#define _SEC_IN_MINUTE 60

#define _SEC_IN_HOUR 3600

#define _SEC_IN_DAY 86400

static _CONST int DAYS_IN_MONTH[12] =

{31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

#define _DAYS_IN_MONTH(x) ((x == 1) ? days_in_feb : DAYS_IN_MONTH[x])

static _CONST int _DAYS_BEFORE_MONTH[12] =

{0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334};

#define _DAYS_IN_YEAR(year) (((year) % 4) ? 365 : 366)

static void

validate_structure (tim_p)

     struct tm *tim_p;

{

  div_t res;

  int days_in_feb = 28;

  /* calculate time & date to account for out of range values */

  if (tim_p->tm_sec < 0 || tim_p->tm_sec > 59)

    {

      res = div (tim_p->tm_sec, 60);

      tim_p->tm_min += res.quot;

      if ((tim_p->tm_sec = res.rem) < 0)

        tim_p->tm_sec += 60;

    }

  if (tim_p->tm_min < 0 || tim_p->tm_min > 59)

    {

      res = div (tim_p->tm_min, 60);

      tim_p->tm_hour += res.quot;

      if ((tim_p->tm_min = res.rem) < 0)

        tim_p->tm_min += 60;

    }

  if (tim_p->tm_hour < 0 || tim_p->tm_hour > 23)

    {

      res = div (tim_p->tm_hour, 24);

      tim_p->tm_mday += res.quot;

      if ((tim_p->tm_hour = res.rem) < 0)

        tim_p->tm_hour += 24;

    }

  if (tim_p->tm_mon > 11)

    {

      res = div (tim_p->tm_mon, 12);

      tim_p->tm_year += res.quot;

      if ((tim_p->tm_mon = res.rem) < 0)

        tim_p->tm_mon += 12;

    }

  if (_DAYS_IN_YEAR (tim_p->tm_year) == 366)

    days_in_feb = 29;

  if (tim_p->tm_mday < 0)

    {

      while (tim_p->tm_mday < 0)

        {

          tim_p->tm_mday += _DAYS_IN_MONTH (tim_p->tm_mon);

          if (--tim_p->tm_mon == -1)

            {

              tim_p->tm_year--;

              tim_p->tm_mon = 12;

              days_in_feb =

                ((_DAYS_IN_YEAR (tim_p->tm_year) == 366) ?

                 29 : 28);

            }

        }

    }

  else

    {

      while (tim_p->tm_mday > _DAYS_IN_MONTH (tim_p->tm_mon))

        {

          tim_p->tm_mday -= _DAYS_IN_MONTH (tim_p->tm_mon);

          if (++tim_p->tm_mon == 12)

            {

              tim_p->tm_year++;

              tim_p->tm_mon = 0;

              days_in_feb =

                ((_DAYS_IN_YEAR (tim_p->tm_year) == 366) ?

                 29 : 28);

            }

        }

    }

}

time_t

mktime (tim_p)

     struct tm *tim_p;

{

  time_t tim = 0;

  long days = 0;

  int year;

  /* validate structure */

  validate_structure (tim_p);

  /* compute hours, minutes, seconds */

  tim += tim_p->tm_sec + (tim_p->tm_min * _SEC_IN_MINUTE) +

    (tim_p->tm_hour * _SEC_IN_HOUR);

  /* compute days in year */

  days += tim_p->tm_mday - 1;

  days += _DAYS_BEFORE_MONTH[tim_p->tm_mon];

  if (tim_p->tm_mon > 1 && _DAYS_IN_YEAR (tim_p->tm_year) == 366)

    days++;

  /* compute day of the year */

  tim_p->tm_yday = days;

  if (tim_p->tm_year > 10000

      || tim_p->tm_year < -10000)

    {

      return (time_t) -1;

    }

  /* compute days in other years */

  if (tim_p->tm_year > 70)

    {

      for (year = 70; year < tim_p->tm_year; year++)

        days += _DAYS_IN_YEAR (year);

    }

  else if (tim_p->tm_year < 70)

    {

      for (year = 69; year > tim_p->tm_year; year--)

        days -= _DAYS_IN_YEAR (year);

      days -= _DAYS_IN_YEAR (year);

    }

  /* compute day of the week */

  if ((tim_p->tm_wday = (days + 4) % 7) < 0)

    tim_p->tm_wday += 7;

  /* compute total seconds */

  tim += (days * _SEC_IN_DAY);

  return tim;

}