158 lines
5.8 KiB
C
158 lines
5.8 KiB
C
/***
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*loctim64.c - Convert __time64_t value to time structure
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*
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* Copyright (c) 1998-2001, Microsoft Corporation. All rights reserved.
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*
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*Purpose:
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* Converts time stored as a __time64_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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* 05-11-98 GJF Created, adapted from the Win64 version.
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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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*
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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 *_localtime64(ptime) - convert __time64_t value to tm structure
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*
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*Purpose:
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* Convert a value in 64-bit internal (__time64_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, _gtime64, localtime and _localtime64() all use a single
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* statically allocated buffer. Each call to one of these routines
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* destroys the contents of the previous call.
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* (3) It is assumed that __time64_t is a 64-bit 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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* __time64_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 _localtime64 (
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const __time64_t *ptime
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)
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{
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REG1 struct tm *ptm;
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__time64_t ltime;
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/*
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* Check for illegal __time64_t value
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*/
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if ( (*ptime < 0) || (*ptime > _MAX__TIME64_T) )
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return( NULL );
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__tzset();
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if ( *ptime > 3 * _DAY_SEC ) {
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/*
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* The date does not fall within the first three representable
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* days of the Epoch. Therefore, there is no possibility of
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* underflowing the __time64_t representation as we compensate
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* for timezone and Daylight Savings Time.
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*/
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ltime = *ptime - _timezone;
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ptm = _gmtime64( <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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ltime -= _dstbias;
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ptm = _gmtime64( <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 = _gmtime64( ptime );
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/*
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* The date falls with the first three days of the Epoch.
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* It is possible the time_t representation would underflow
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* while compensating for timezone and Daylight Savings Time
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* Therefore, make the timezone and Daylight Savings Time
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* adjustments directly in the tm structure. The beginning of
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* the Epoch is 00:00:00, 01-01-70 (UTC).
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*
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* First, adjust for the timezone.
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*/
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if ( _isindst(ptm) ) {
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ltime = (__time64_t)ptm->tm_sec - (_timezone + _dstbias);
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ptm->tm_isdst;
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}
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else
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ltime = (__time64_t)ptm->tm_sec - _timezone;
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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 = (__time64_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 = (__time64_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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* 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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}
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return(ptm);
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}
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