/*
   * Copyright (C) 1993, 1994, 1995, 1996, 1997 Free Software Foundation, Inc.
   * This file is part of the GNU C Library.
   * Contributed by Paul Eggert (eggert@twinsun.com).
   *
   * The GNU C Library is free software; you can redistribute it and/or
   * modify it under the terms of the GNU Library General Public License as
   * published by the Free Software Foundation; either version 2 of the
   * License, or (at your option) any later version.
   *
   * The GNU C Library is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   * Library General Public License for more details.
   *
   * You should have received a copy of the GNU Library General Public
   * License along with the GNU C Library; see the file COPYING.LIB.  If not,
   * write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   * Boston, MA 02111-1307, USA.
   */
  
  /*
   * Converts the calendar time to broken-down time representation
   * Based on code from glibc-2.6
   *
   * 2009-7-14:
   *   Moved from glibc-2.6 to kernel by Zhaolei<zhaolei@cn.fujitsu.com>
   */
  
  #include <linux/time.h>
  #include <linux/module.h>
  
  /*
   * Nonzero if YEAR is a leap year (every 4 years,
   * except every 100th isn't, and every 400th is).
   */
  static int __isleap(long year)
  {
  	return (year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0);
  }
  
  /* do a mathdiv for long type */
  static long math_div(long a, long b)
  {
  	return a / b - (a % b < 0);
  }
  
  /* How many leap years between y1 and y2, y1 must less or equal to y2 */
  static long leaps_between(long y1, long y2)
  {
  	long leaps1 = math_div(y1 - 1, 4) - math_div(y1 - 1, 100)
  		+ math_div(y1 - 1, 400);
  	long leaps2 = math_div(y2 - 1, 4) - math_div(y2 - 1, 100)
  		+ math_div(y2 - 1, 400);
  	return leaps2 - leaps1;
  }
  
  /* How many days come before each month (0-12). */
  static const unsigned short __mon_yday[2][13] = {
  	/* Normal years. */
  	{0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365},
  	/* Leap years. */
  	{0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366}
  };
  
  #define SECS_PER_HOUR	(60 * 60)
  #define SECS_PER_DAY	(SECS_PER_HOUR * 24)
  
  /**
   * time_to_tm - converts the calendar time to local broken-down time
   *
   * @totalsecs	the number of seconds elapsed since 00:00:00 on January 1, 1970,
   *		Coordinated Universal Time (UTC).
   * @offset	offset seconds adding to totalsecs.
   * @result	pointer to struct tm variable to receive broken-down time
   */
  void time_to_tm(time_t totalsecs, int offset, struct tm *result)
  {
  	long days, rem, y;
  	const unsigned short *ip;
  
  	days = totalsecs / SECS_PER_DAY;
  	rem = totalsecs % SECS_PER_DAY;
  	rem += offset;
  	while (rem < 0) {
  		rem += SECS_PER_DAY;
  		--days;
  	}
  	while (rem >= SECS_PER_DAY) {
  		rem -= SECS_PER_DAY;
  		++days;
  	}
  
  	result->tm_hour = rem / SECS_PER_HOUR;
  	rem %= SECS_PER_HOUR;
  	result->tm_min = rem / 60;
  	result->tm_sec = rem % 60;
  
  	/* January 1, 1970 was a Thursday. */
  	result->tm_wday = (4 + days) % 7;
  	if (result->tm_wday < 0)
  		result->tm_wday += 7;
  
  	y = 1970;
  
  	while (days < 0 || days >= (__isleap(y) ? 366 : 365)) {
  		/* Guess a corrected year, assuming 365 days per year. */
  		long yg = y + math_div(days, 365);
  
  		/* Adjust DAYS and Y to match the guessed year. */
  		days -= (yg - y) * 365 + leaps_between(y, yg);
  		y = yg;
  	}
  
  	result->tm_year = y - 1900;
  
  	result->tm_yday = days;
  
  	ip = __mon_yday[__isleap(y)];
  	for (y = 11; days < ip[y]; y--)
  		continue;
  	days -= ip[y];
  
  	result->tm_mon = y;
  	result->tm_mday = days + 1;
  }
  EXPORT_SYMBOL(time_to_tm);