/***
*localtim.c - Convert time_t value to time structure
*
* Copyright (c) 1985-1993, Microsoft Corporation. All rights reserved.
*
*Purpose:
* Converts time stored as a time_t value to a structure of type
* struct tm expressed as local time.
*
*Revision History:
* 01-??-84 RLB Module created
* 05-??-84 DCW split off from the rest of the ctime routines
* 02-18-87 JCR made localtime work when gmtime returns null
* 03-31-87 JCR fixed bug pertaining to uninitialized _isindst(tb)
* 04-10-87 JCR changed long declaration to time_t and added const
* 11-10-87 SKS Removed IBMC20 switch
* 11-18-87 SKS Change tzset() to __tzset()
* 12-11-87 JCR Added "_LOAD_DS" to declaration
* 11-06-89 KRS Added (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. Also, rewrote expr.
* to avoid using cast as lvalue.
* 01-21-91 GJF ANSI naming.
* 08-10-92 PBS Posix support (TZ stuff).
* 03-24-93 GJF Ported C8-16 version and adapted for exotic Daylight
* Savings Time conversions which are legal under POSIX.
* 07-15-93 GJF Replaced _tzset() call with __tzset() call.
*
*******************************************************************************/
#include <cruntime.h>
#include <limits.h>
#include <time.h>
#include <stddef.h>
#include <ctime.h>
#include <internal.h>
/***
*struct tm *localtime(ptime) - convert time_t value to tm structure
*
*Purpose:
* Convert a value in internal (time_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 and localtime 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 time_t is a 32-bit long 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:
* time_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 * _CRTAPI1 localtime (
const time_t *ptime
)
{
REG1 struct tm *ptm;
long ltime;
/*
* Check for illegal time_t value
*/
if ( (long)*ptime < 0L )
return( NULL );
#ifdef _POSIX_
tzset();
#else
__tzset();
#endif
if ( (*ptime > 3 * _DAY_SEC) && (*ptime < LONG_MAX - 3 * _DAY_SEC) ) {
/*
* The date does not fall within the first three, or last
* three, representable days of the Epoch. Therefore, there
* is no possibility of overflowing or underflowing the
* time_t representation as we compensate for timezone and
* Daylight Savings Time.
*/
ltime = (long)*ptime - _timezone;
ptm = gmtime( <ime );
/*
* Check and adjust for Daylight Saving Time.
*/
if ( _daylight && _isindst( ptm ) ) {
#ifdef _POSIX_
ltime -= _dstoffset - _timezone;
#else
ltime += 3600L;
#endif
ptm = gmtime( (time_t *)<ime );
ptm->tm_isdst = 1;
}
}
else {
ptm = gmtime( ptime );
/*
* The date falls with the first three, or last three days
* of the Epoch. It is possible the time_t representation
* would overflow or 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) and the last representable second
* in theEpoch is 03:14:07, 01-19-2038 (UTC). This will be
* used in the calculations below.
*
* First, adjust for the timezone.
*/
ltime = (long)ptm->tm_sec - _timezone;
ptm->tm_sec = (int)(ltime % 60);
if ( ptm->tm_sec < 0 ) {
ptm->tm_sec += 60;
ltime -= 60;
}
ltime = (long)ptm->tm_min + ltime/60;
ptm->tm_min = (int)(ltime % 60);
if ( ptm->tm_min < 0 ) {
ptm->tm_min += 60;
ltime -= 60;
}
ltime = (long)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 > 0L ) {
/*
* There is no possibility of overflowing the tm_mday
* and tm_yday fields since the date can be no later
* than January 19.
*/
ptm->tm_wday = (ptm->tm_wday + ltime) % 7;
ptm->tm_mday += ltime;
ptm->tm_yday += ltime;
}
else if ( ltime < 0L ) {
/*
* 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 + ltime) % 7;
if ( (ptm->tm_mday += ltime) <= 0 ) {
ptm->tm_mday += 31;
ptm->tm_yday = 365;
ptm->tm_mon = 11;
ptm->tm_year--;
}
else {
ptm->tm_yday += ltime;
}
}
#ifdef _POSIX_
/*
* In Posix, it is possible either the first or last three
* days of the Epoch might lie with Daylight Savings Time in
* certain time zones.
*/
if ( _isindst(ptm) ) {
ltime = (long)ptm->tm_sec + _dstoffset;
ptm->tm_sec = (int)(ltime % 60);
if ( ptm->tm_sec < 0 ) {
ptm->tm_sec += 60;
ltime -= 60;
}
ltime = (long)ptm->tm_min + ltime/60;
ptm->tm_min = (int)(ltime % 60);
if ( ptm->tm_min < 0 ) {
ptm->tm_min += 60;
ltime -= 60;
}
ltime = (long)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 > 0L ) {
/*
* There is no possibility of overflowing the
* tm_mday and tm_yday fields since the date
* can be no later than January 19.
*/
ptm->tm_wday = (ptm->tm_wday + ltime) % 7;
ptm->tm_mday += ltime;
ptm->tm_yday += ltime;
}
else if ( ltime < 0L ) {
/*
* 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 + ltime) % 7;
if ( (ptm->tm_mday += ltime) <= 0 ) {
ptm->tm_mday += 31;
ptm->tm_yday = 365;
ptm->tm_mon = 12;
ptm->tm_year--;
}
else {
ptm->tm_yday += ltime;
}
}
}
#endif
}
return(ptm);
}
