284 lines
11 KiB
C
284 lines
11 KiB
C
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/***
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*localtim.c - Convert time_t value to time structure
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*
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* Copyright (c) 1985-2001, Microsoft Corporation. All rights reserved.
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*
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*Purpose:
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* Converts time stored as a time_t value to a structure of type
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* struct tm expressed as local time.
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*
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*Revision History:
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* 01-??-84 RLB Module created
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* 05-??-84 DCW split off from the rest of the ctime routines
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* 02-18-87 JCR made localtime work when gmtime returns null
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* 03-31-87 JCR fixed bug pertaining to uninitialized _isindst(tb)
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* 04-10-87 JCR changed long declaration to time_t and added const
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* 11-10-87 SKS Removed IBMC20 switch
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* 11-18-87 SKS Change tzset() to __tzset()
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* 12-11-87 JCR Added "_LOAD_DS" to declaration
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* 11-06-89 KRS Added (unsigned) to handle years 2040-2099 correctly.
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* 03-20-90 GJF Replaced _LOAD_DS with _CALLTYPE1, added #include
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* <cruntime.h>, removed #include <register.h> and
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* fixed the copyright. Also, cleaned up the formatting
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* a bit.
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* 10-04-90 GJF New-style function declarator. Also, rewrote expr.
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* to avoid using cast as lvalue.
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* 01-21-91 GJF ANSI naming.
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* 08-10-92 PBS Posix support (TZ stuff).
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* 03-24-93 GJF Ported C8-16 version and adapted for exotic Daylight
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* Savings Time conversions which are legal under POSIX.
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* 04-06-93 SKS Replace _CRTAPI* with __cdecl
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* 07-15-93 GJF Replaced _tzset() call with __tzset() call.
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* 09-20-93 GJF Merged NT SDK and Cuda version (amount to picking up
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* fixes to Posix build).
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* 11-04-93 GJF Picked up a fix for the Posix build.
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* 02-13-95 GJF Call _tzset for Mac builds (temp change?). Also,
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* picked up bug fix from Mac version (setting of
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* tm_yday field in underflow case).
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* 08-31-95 GJF Use _dstbias as the Daylight Saving Time bias and
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* all for the beginning or end of the Epoch to be in a
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* DST.
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* 02-07-98 GJF Changes for Win64: replaced long type with time_t,
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* added some int casts where required, also use __int64
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* max value for bounds checking.
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* 09-25-98 GJF Set tm_isdst, when appropriate, at beginning/end of the
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* Epoch
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* 05-17-99 PML Remove all Macintosh support.
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* 11-03-99 RDL Win64 POSIX warning fix.
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*
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*******************************************************************************/
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#include <cruntime.h>
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#include <limits.h>
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#include <time.h>
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#include <stddef.h>
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#include <ctime.h>
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#include <internal.h>
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/***
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*struct tm *localtime(ptime) - convert time_t value to tm structure
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*
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*Purpose:
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* Convert a value in internal (time_t) format to a tm struct
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* containing the corresponding local time.
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*
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* NOTES:
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* (1) gmtime must be called before _isindst to ensure that the tb time
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* structure is initialized.
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* (2) gmtime and localtime use a single statically allocated buffer.
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* Each call to one of these routines destroys the contents of the
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* previous call.
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* (3) It is assumed that time_t is a 32-bit long integer representing
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* the number of seconds since 00:00:00, 01-01-70 (UTC) (i.e., the
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* Posix/Unix Epoch. Only non-negative values are supported.
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* (4) It is assumed that the maximum adjustment for local time is
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* less than three days (include Daylight Savings Time adjustment).
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* This only a concern in Posix where the specification of the TZ
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* environment restricts the combined offset for time zone and
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* Daylight Savings Time to 2 * (24:59:59), just under 50 hours.
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*
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*Entry:
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* time_t *ptime - pointer to a long time value
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*
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*Exit:
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* If *ptime is non-negative, returns a pointer to the tm structure.
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* Otherwise, returns NULL.
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*
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*Exceptions:
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* See items (3) and (4) in the NOTES above. If these assumptions are
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* violated, behavior is undefined.
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*
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*******************************************************************************/
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struct tm * __cdecl localtime (
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const time_t *ptime
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)
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{
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REG1 struct tm *ptm;
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time_t ltime;
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/*
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* Check for illegal time_t value
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*/
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if ( *ptime < 0 )
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return( NULL );
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#ifdef _POSIX_
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tzset();
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#else
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__tzset();
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#endif
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#ifdef _WIN64
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if ( (*ptime > 3 * _DAY_SEC) && (*ptime < _I64_MAX - 3 * _DAY_SEC) ) {
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#else
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if ( (*ptime > 3 * _DAY_SEC) && (*ptime < LONG_MAX - 3 * _DAY_SEC) ) {
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#endif
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/*
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* The date does not fall within the first three, or last
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* three, representable days of the Epoch. Therefore, there
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* is no possibility of overflowing or underflowing the
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* time_t representation as we compensate for timezone and
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* Daylight Savings Time.
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*/
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ltime = *ptime - _timezone;
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ptm = gmtime( <ime );
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/*
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* Check and adjust for Daylight Saving Time.
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*/
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if ( _daylight && _isindst( ptm ) ) {
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#ifdef _POSIX_
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ltime -= _dstoffset - _timezone;
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#else
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ltime -= _dstbias;
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#endif
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ptm = gmtime( <ime );
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ptm->tm_isdst = 1;
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}
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}
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else {
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ptm = gmtime( ptime );
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/*
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* The date falls with the first three, or last three days
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* of the Epoch. It is possible the time_t representation
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* would overflow or underflow while compensating for
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* timezone and Daylight Savings Time. Therefore, make the
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* timezone and Daylight Savings Time adjustments directly
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* in the tm structure. The beginning of the Epoch is
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* 00:00:00, 01-01-70 (UTC) and the last representable second
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* in the Epoch is 03:14:07, 01-19-2038 (UTC). This will be
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* used in the calculations below.
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*
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* First, adjust for the timezone.
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*/
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#ifdef _POSIX_
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ltime = (time_t)ptm->tm_sec - _timezone;
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#else
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if ( _daylight && _isindst(ptm) ) {
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ltime = (time_t)ptm->tm_sec - (_timezone + _dstbias);
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ptm->tm_isdst = 1;
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}
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else
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ltime = (time_t)ptm->tm_sec - _timezone;
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#endif
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ptm->tm_sec = (int)(ltime % 60);
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if ( ptm->tm_sec < 0 ) {
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ptm->tm_sec += 60;
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ltime -= 60;
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}
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ltime = (time_t)ptm->tm_min + ltime/60;
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ptm->tm_min = (int)(ltime % 60);
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if ( ptm->tm_min < 0 ) {
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ptm->tm_min += 60;
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ltime -= 60;
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}
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ltime = (time_t)ptm->tm_hour + ltime/60;
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ptm->tm_hour = (int)(ltime % 24);
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if ( ptm->tm_hour < 0 ) {
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ptm->tm_hour += 24;
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ltime -=24;
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}
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ltime /= 24;
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if ( ltime > 0 ) {
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/*
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* There is no possibility of overflowing the tm_mday
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* and tm_yday fields since the date can be no later
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* than January 19.
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*/
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ptm->tm_wday = (ptm->tm_wday + (int)ltime) % 7;
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ptm->tm_mday += (int)ltime;
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ptm->tm_yday += (int)ltime;
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}
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else if ( ltime < 0 ) {
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/*
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* It is possible to underflow the tm_mday and tm_yday
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* fields. If this happens, then adjusted date must
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* lie in December 1969.
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*/
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ptm->tm_wday = (ptm->tm_wday + 7 + (int)ltime) % 7;
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if ( (ptm->tm_mday += (int)ltime) <= 0 ) {
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ptm->tm_mday += 31;
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ptm->tm_yday = 364;
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ptm->tm_mon = 11;
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ptm->tm_year--;
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}
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else {
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ptm->tm_yday += (int)ltime;
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}
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}
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#ifdef _POSIX_
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/*
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* In Posix, it is possible either the first or last three
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* days of the Epoch might lie with Daylight Savings Time in
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* certain time zones.
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*/
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if ( _isindst(ptm) ) {
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ltime = (long)ptm->tm_sec + _dstoffset;
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ptm->tm_sec = (int)(ltime % 60);
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if ( ptm->tm_sec < 0 ) {
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ptm->tm_sec += 60;
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ltime -= 60;
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}
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ltime = (long)ptm->tm_min + ltime/60;
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ptm->tm_min = (int)(ltime % 60);
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if ( ptm->tm_min < 0 ) {
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ptm->tm_min += 60;
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ltime -= 60;
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}
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ltime = (long)ptm->tm_hour + ltime/60;
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ptm->tm_hour = (int)(ltime % 24);
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if ( ptm->tm_hour < 0 ) {
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ptm->tm_hour += 24;
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ltime -=24;
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}
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ltime /= 24;
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if ( ltime > 0L ) {
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/*
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* There is no possibility of overflowing the
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* tm_mday and tm_yday fields since the date
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* can be no later than January 19.
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*/
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ptm->tm_wday = (int)((ptm->tm_wday + ltime) % 7);
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ptm->tm_mday += (int)ltime;
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ptm->tm_yday += (int)ltime;
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}
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else if ( ltime < 0L ) {
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/*
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* It is possible to underflow the tm_mday
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* and tm_yday fields. If this happens, then
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* adjusted date must lie in December 1969.
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*/
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ptm->tm_wday = (int)((ptm->tm_wday + 7 + ltime) % 7);
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if ( (ptm->tm_mday += (int)ltime) <= 0 ) {
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ptm->tm_mday += 31;
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ptm->tm_yday = 364;
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ptm->tm_mon = 11;
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ptm->tm_year--;
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}
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else {
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ptm->tm_yday += (int)ltime;
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}
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}
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}
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#endif
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}
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return(ptm);
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}
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