windows-nt/Source/XPSP1/NT/base/crts/crtw32/time/loctim64.c

/***
*loctim64.c - Convert __time64_t value to time structure
*
*       Copyright (c) 1998-2001, Microsoft Corporation. All rights reserved.
*
*Purpose:
*       Converts time stored as a __time64_t value to a structure of type
*       struct tm expressed as local time.
*
*Revision History:
*       05-11-98  GJF   Created, adapted from the Win64 version.
*       09-25-98  GJF   Set tm_isdst, when appropriate, at beginning/end of the
*                       Epoch
*
*******************************************************************************/

#include <cruntime.h>
#include <limits.h>
#include <time.h>
#include <stddef.h>
#include <ctime.h>
#include <internal.h>

/***
*struct tm *_localtime64(ptime) - convert __time64_t value to tm structure
*
*Purpose:
*       Convert a value in 64-bit internal (__time64_t) format to a tm struct
*       containing the corresponding local time.
*
* NOTES:
*       (1) gmtime must be called before _isindst to ensure that the tb time
*           structure is initialized.
*       (2) gmtime, _gtime64, localtime and _localtime64() all use a single 
*           statically allocated buffer. Each call to one of these routines 
*           destroys the contents of the previous call.
*       (3) It is assumed that __time64_t is a 64-bit integer representing
*           the number of seconds since 00:00:00, 01-01-70 (UTC) (i.e., the
*           Posix/Unix Epoch. Only non-negative values are supported.
*       (4) It is assumed that the maximum adjustment for local time is
*           less than three days (include Daylight Savings Time adjustment).
*           This only a concern in Posix where the specification of the TZ
*           environment restricts the combined offset for time zone and
*           Daylight Savings Time to 2 * (24:59:59), just under 50 hours.
*
*Entry:
*       __time64_t *ptime - pointer to a long time value
*
*Exit:
*       If *ptime is non-negative, returns a pointer to the tm structure.
*       Otherwise, returns NULL.
*
*Exceptions:
*       See items (3) and (4) in the NOTES above. If these assumptions are
*       violated, behavior is undefined.
*
*******************************************************************************/

struct tm * __cdecl _localtime64 (
        const __time64_t *ptime
        )
{
        REG1 struct tm *ptm;
        __time64_t ltime;

        /*
         * Check for illegal __time64_t value
         */
        if ( (*ptime < 0) || (*ptime > _MAX__TIME64_T) )
                return( NULL );

        __tzset();

        if ( *ptime > 3 * _DAY_SEC ) {
                /*
                 * The date does not fall within the first three representable
                 * days of the Epoch. Therefore, there is no possibility of 
                 * underflowing the __time64_t representation as we compensate 
                 * for timezone and Daylight Savings Time.
                 */

                ltime = *ptime - _timezone;
                ptm = _gmtime64( &ltime );

                /*
                 * Check and adjust for Daylight Saving Time.
                 */
                if ( _daylight && _isindst( ptm ) ) {
                        ltime -= _dstbias;
                        ptm = _gmtime64( &ltime );
                        ptm->tm_isdst = 1;
                }
        }
        else {
                ptm = _gmtime64( ptime );

                /*
                 * The date falls with the first three days of the Epoch.
                 * It is possible the time_t representation would underflow
                 * while compensating for timezone and Daylight Savings Time
                 * Therefore, make the timezone and Daylight Savings Time
                 * adjustments directly in the tm structure. The beginning of
                 * the Epoch is 00:00:00, 01-01-70 (UTC).
                 *
                 * First, adjust for the timezone.
                 */
                if ( _isindst(ptm) ) {
                        ltime = (__time64_t)ptm->tm_sec - (_timezone + _dstbias);
                        ptm->tm_isdst;
                }
                else
                        ltime = (__time64_t)ptm->tm_sec - _timezone;

                ptm->tm_sec = (int)(ltime % 60);
                if ( ptm->tm_sec < 0 ) {
                        ptm->tm_sec += 60;
                        ltime -= 60;
                }

                ltime = (__time64_t)ptm->tm_min + ltime/60;
                ptm->tm_min = (int)(ltime % 60);
                if ( ptm->tm_min < 0 ) {
                        ptm->tm_min += 60;
                        ltime -= 60;
                }

                ltime = (__time64_t)ptm->tm_hour + ltime/60;
                ptm->tm_hour = (int)(ltime % 24);
                if ( ptm->tm_hour < 0 ) {
                        ptm->tm_hour += 24;
                        ltime -=24;
                }

                ltime /= 24;

                if ( ltime < 0 ) {
                        /*
                         * It is possible to underflow the tm_mday and tm_yday
                         * fields. If this happens, then adjusted date must
                         * lie in December 1969.
                         */
                        ptm->tm_wday = (ptm->tm_wday + 7 + (int)ltime) % 7;
                        if ( (ptm->tm_mday += (int)ltime) <= 0 ) {
                                ptm->tm_mday += 31;
                                ptm->tm_yday = 364;
                                ptm->tm_mon = 11;
                                ptm->tm_year--;
                        }
                        else {
                                ptm->tm_yday += (int)ltime;
                        }
                }
        }


        return(ptm);
}