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/*

 * localtime_r.c

 * Original Author:     Adapted from tzcode maintained by Arthur David Olson.

 *

 * Converts the calendar time pointed to by tim_p into a broken-down time

 * expressed as local time. Returns a pointer to a structure containing the

 * broken-down time.

 */

#include <stdlib.h>

#include <time.h>

#define SECSPERMIN      60L

#define MINSPERHOUR     60L

#define HOURSPERDAY     24L

#define SECSPERHOUR     (SECSPERMIN * MINSPERHOUR)

#define SECSPERDAY      (SECSPERHOUR * HOURSPERDAY)

#define DAYSPERWEEK     7

#define MONSPERYEAR     12

#define YEAR_BASE       1900

#define EPOCH_YEAR      1970

#define EPOCH_WDAY      4

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

static _CONST int mon_lengths[2][MONSPERYEAR] = {

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

  {31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}

} ;

static _CONST int year_lengths[2] = {

  365,

  366

} ;

struct tm *

_DEFUN (localtime_r, (tim_p, res),

        _CONST time_t * tim_p _AND

        struct tm *res)

{

  long days, rem;

  int y;

  int yleap;

  _CONST int *ip;

  days = ((long) *tim_p) / SECSPERDAY;

  rem = ((long) *tim_p) % SECSPERDAY;

  while (rem < 0)

    {

      rem += SECSPERDAY;

      --days;

    }

  while (rem >= SECSPERDAY)

    {

      rem -= SECSPERDAY;

      ++days;

    }

  /* compute hour, min, and sec */

  res->tm_hour = (int) (rem / SECSPERHOUR);

  rem %= SECSPERHOUR;

  res->tm_min = (int) (rem / SECSPERMIN);

  res->tm_sec = (int) (rem % SECSPERMIN);

  /* compute day of week */

  if ((res->tm_wday = ((EPOCH_WDAY + days) % DAYSPERWEEK)) < 0)

    res->tm_wday += DAYSPERWEEK;

  /* compute year & day of year */

  y = EPOCH_YEAR;

  if (days >= 0)

    {

      for (;;)

        {

          yleap = isleap(y);

          if (days < year_lengths[yleap])

            break;

          y++;

          days -= year_lengths[yleap];

        }

    }

  else

    {

      do

        {

          --y;

          yleap = isleap(y);

          days += year_lengths[yleap];

        } while (days < 0);

    }

  res->tm_year = y - YEAR_BASE;

  res->tm_yday = days;

  ip = mon_lengths[yleap];

  for (res->tm_mon = 0; days >= ip[res->tm_mon]; ++res->tm_mon)

    days -= ip[res->tm_mon];

  res->tm_mday = days + 1;

  /* set daylight saving time flag */

  res->tm_isdst = -1;

  return (res);

}