windows-nt-4.0/private/crt32/time/gmtime.c

/***
*gmtime.c - breaks down a time value into GMT date/time info
*
*	Copyright (c) 1985-1993, Microsoft Corporation. All rights reserved.
*
*Purpose:
*	defines gmtime() - breaks the clock value down into GMT time/date
*	information; return pointer to structure with the data.
*
*Revision History:
*	01-??-84  RLB	Module created
*	05-??-84  DCW	Split off from rest off ctime routines.
*	02-18-87  JCR	For MS C, gmtime now returns NULL for out of range
*			time/date.	(This is for ANSI compatibility.)
*	04-10-87  JCR	Changed long declaration to time_t and added const
*	05-21-87  SKS	Declare "struct tm tb" as NEAR data
*	11-10-87  SKS	Removed IBMC20 switch
*	12-11-87  JCR	Added "_LOAD_DS" to declaration
*	05-24-88  PHG	Merge DLL and regular versions
*	06-06-89  JCR	386 mthread support
*	11-06-89  KRS	Add (unsigned) to handle years 2040-2099 correctly
*	03-20-90  GJF	Replaced _LOAD_DS with _CALLTYPE1, added #include
*			<cruntime.h>, removed #include <register.h> and
*			fixed the copyright. Also, cleaned up the formatting
*			a bit.
*	10-04-90  GJF	New-style function declarator.
*	07-17-91  GJF	Multi-thread support for Win32 [_WIN32_].
*	02-17-93  GJF	Changed for new _getptd().
*	03-24-93  GJF	Propagated changes from 16-bit tree.
*
*******************************************************************************/

#include <cruntime.h>
#include <time.h>
#include <ctime.h>
#include <stddef.h>
#include <internal.h>
#include <os2dll.h>
#ifdef MTHREAD
#include <malloc.h>
#include <stddef.h>
#endif

static struct tm tb = { 0 };	/* time block */

/***
*struct tm *gmtime(timp) - convert *timp to a structure (UTC)
*
*Purpose:
*	Converts the calendar time value, in internal format (time_t), to
*	broken-down time (tm structure) with the corresponding UTC time.
*
*Entry:
*	const time_t *timp - pointer to time_t value to convert
*
*Exit:
*	returns pointer to filled-in tm structure.
*	returns NULL if *timp < 0L
*
*Exceptions:
*
*******************************************************************************/

struct tm * _CRTAPI1 gmtime (
	const time_t *timp
	)
{

	long caltim = *timp;		/* calendar time to convert */
	int islpyr = 0; 		/* is-current-year-a-leap-year flag */
	REG1 int tmptim;
	REG3 int *mdays;		/* pointer to days or lpdays */

#ifdef	MTHREAD

	REG2 struct tm *ptb;		/* will point to gmtime buffer */
	_ptiddata ptd = _getptd();

#else
	REG2 struct tm *ptb = &tb;
#endif

	if ( caltim < 0L )
		return(NULL);

#ifdef	MTHREAD

	/* Use per thread buffer area (malloc space, if necessary) */

	if ( (ptd->_gmtimebuf != NULL) || ((ptd->_gmtimebuf =
	    malloc(sizeof(struct tm))) != NULL) )
		ptb = ptd->_gmtimebuf;
	else
		ptb = &tb;	/* malloc error: use static buffer */

#endif

	/*
	 * Determine years since 1970. First, identify the four-year interval
	 * since this makes handling leap-years easy (note that 2000 IS a
	 * leap year and 2100 is out-of-range).
	 */
	tmptim = (int)(caltim / _FOUR_YEAR_SEC);
	caltim -= ((long)tmptim * _FOUR_YEAR_SEC);

	/*
	 * Determine which year of the interval
	 */
	tmptim = (tmptim * 4) + 70;	    /* 1970, 1974, 1978,...,etc. */

	if ( caltim >= _YEAR_SEC ) {

	    tmptim++;			    /* 1971, 1975, 1979,...,etc. */
	    caltim -= _YEAR_SEC;

	    if ( caltim >= _YEAR_SEC ) {

		tmptim++;		    /* 1972, 1976, 1980,...,etc. */
		caltim -= _YEAR_SEC;

		/*
		 * Note, it takes 366 days-worth of seconds to get past a leap
		 * year.
		 */
		if ( caltim >= (_YEAR_SEC + _DAY_SEC) ) {

			tmptim++;	    /* 1973, 1977, 1981,...,etc. */
			caltim -= (_YEAR_SEC + _DAY_SEC);
		}
		else {
			/*
			 * In a leap year after all, set the flag.
			 */
			islpyr++;
		}
	    }
	}

	/*
	 * tmptim now holds the value for tm_year. caltim now holds the
	 * number of elapsed seconds since the beginning of that year.
	 */
	ptb->tm_year = tmptim;

	/*
	 * Determine days since January 1 (0 - 365). This is the tm_yday value.
	 * Leave caltim with number of elapsed seconds in that day.
	 */
	ptb->tm_yday = (int)(caltim / _DAY_SEC);
	caltim -= (long)(ptb->tm_yday) * _DAY_SEC;

	/*
	 * Determine months since January (0 - 11) and day of month (1 - 31)
	 */
	if ( islpyr )
	    mdays = _lpdays;
	else
	    mdays = _days;


	for ( tmptim = 1 ; mdays[tmptim] < ptb->tm_yday ; tmptim++ ) ;

	ptb->tm_mon = --tmptim;

	ptb->tm_mday = ptb->tm_yday - mdays[tmptim];

	/*
	 * Determine days since Sunday (0 - 6)
	 */
	ptb->tm_wday = ((int)(*timp / _DAY_SEC) + _BASE_DOW) % 7;

	/*
	 *  Determine hours since midnight (0 - 23), minutes after the hour
	 *  (0 - 59), and seconds after the minute (0 - 59).
	 */
	ptb->tm_hour = (int)(caltim / 3600);
	caltim -= (long)ptb->tm_hour * 3600L;

	ptb->tm_min = (int)(caltim / 60);
	ptb->tm_sec = (int)(caltim - (ptb->tm_min) * 60);

	ptb->tm_isdst = 0;
	return( (struct tm *)ptb );

}