/*** *localtim.c - Convert __time32_t value to time structure * * Copyright (c) Microsoft Corporation. All rights reserved. * *Purpose: * Converts time stored as a __time32_t value to a structure of type * struct tm expressed as local time. * *******************************************************************************/ #include #include #include #include #include #include #include /*** *struct tm *_localtime32_s(ptm, ptime) - convert __time32_t value to tm structure * *Purpose: * Convert a value in 32-bit internal (__time32_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) __time32_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: * __time32_t *ptime - pointer to a long time value * *Exit: * errno_t = 0 success * tm members filled-in * errno_t = non zero * tm members initialized to -1 if ptm != NULL * *Exceptions: * See items (3) and (4) in the NOTES above. If these assumptions are * violated, behavior is undefined. * *******************************************************************************/ errno_t __cdecl _localtime32_s ( struct tm *ptm, const __time32_t *ptime ) { __time32_t ltime; errno_t e = 0; int daylight = 0; long dstbias = 0; long timezone = 0; _VALIDATE_RETURN_ERRCODE( ( ptm != NULL ), EINVAL ) memset( ptm, 0xff, sizeof( struct tm ) ); _VALIDATE_RETURN_ERRCODE( ( ptime != NULL ), EINVAL ) /* * Check for illegal __time32_t value */ _VALIDATE_RETURN_ERRCODE_NOEXC( ( *ptime >= 0 ), EINVAL ) __tzset(); _ERRCHECK(_get_daylight(&daylight)); _ERRCHECK(_get_dstbias(&dstbias)); _ERRCHECK(_get_timezone(&timezone)); 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 * __time32_t representation as we compensate for timezone and * Daylight Savings Time. */ ltime = *ptime - timezone; e = _gmtime32_s( ptm, <ime ); if ( e != 0 ) { return e; } /* * Check and adjust for Daylight Saving Time. */ if ( daylight && _isindst( ptm ) ) { ltime -= dstbias; e = _gmtime32_s( ptm, <ime ); if ( e != 0 ) { return e; } ptm->tm_isdst = 1; } } else { e = _gmtime32_s( ptm, ptime ); if ( e != 0 ) { return e; } /* * The date falls with the first three, or last three days * of the Epoch. It is possible the __time32_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 the Epoch is 03:14:07, 01-19-2038 (UTC). This will be * used in the calculations below. * * First, adjust for the timezone. */ if ( daylight && _isindst(ptm) ) { ltime = (__time32_t)ptm->tm_sec - (timezone + dstbias); ptm->tm_isdst = 1; } else ltime = (__time32_t)ptm->tm_sec - timezone; ptm->tm_sec = (int)(ltime % 60); if ( ptm->tm_sec < 0 ) { ptm->tm_sec += 60; ltime -= 60; } ltime = (__time32_t)ptm->tm_min + ltime/60; ptm->tm_min = (int)(ltime % 60); if ( ptm->tm_min < 0 ) { ptm->tm_min += 60; ltime -= 60; } ltime = (__time32_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 ) { /* * 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 + (int)ltime) % 7; ptm->tm_mday += (int)ltime; ptm->tm_yday += (int)ltime; } else 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; // according to assumption 4 above, timezone can // cause the date to underflow the epoch by // more than a day ptm->tm_yday = ptm->tm_yday + (int)ltime + 365; ptm->tm_mon = 11; ptm->tm_year--; } else { ptm->tm_yday += (int)ltime; } } } return 0; } /*** *struct tm *_localtime32(ptime) - convert __time32_t value to tm structure * *Purpose: * Convert a value in 32-bit internal (__time32_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 __time32_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: * __time32_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 _localtime32 ( const __time32_t *ptime ) { errno_t e; struct tm *ptm = __getgmtimebuf(); if ( ptm == NULL ) { return NULL; } e = _localtime32_s( ptm, ptime ); if ( e != 0 ) { return NULL; } return ptm; }