142 lines
5.3 KiB
C
142 lines
5.3 KiB
C
/****************************************************************************
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*
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* Open Watcom Project
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*
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* Portions Copyright (c) 1983-2002 Sybase, Inc. All Rights Reserved.
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*
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* ========================================================================
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*
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* This file contains Original Code and/or Modifications of Original
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* Code as defined in and that are subject to the Sybase Open Watcom
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* Public License version 1.0 (the 'License'). You may not use this file
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* except in compliance with the License. BY USING THIS FILE YOU AGREE TO
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* ALL TERMS AND CONDITIONS OF THE LICENSE. A copy of the License is
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* provided with the Original Code and Modifications, and is also
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* available at www.sybase.com/developer/opensource.
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*
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* The Original Code and all software distributed under the License are
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* distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
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* EXPRESS OR IMPLIED, AND SYBASE AND ALL CONTRIBUTORS HEREBY DISCLAIM
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* ALL SUCH WARRANTIES, INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR
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* NON-INFRINGEMENT. Please see the License for the specific language
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* governing rights and limitations under the License.
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*
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* ========================================================================
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*
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* Description: __brktime() is an internal function to convert time to struct tm
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*
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****************************************************************************/
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#include "variety.h"
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#include <time.h>
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#include "thetime.h"
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#include "timedata.h"
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// #define DAYS_IN_4_YRS ( 365 + 365 + 365 + 366 )
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// #define DAYS_IN_400_YRS ( ( 100 * DAYS_IN_4_YRS ) - 3 )
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// #define SECONDS_PER_DAY ( 24 * 60 * 60 )
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// extern short __diyr[], __dilyr[];
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/*
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The number of leap years from year 1 to year 1900 is 460.
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The number of leap years from year 1 to current year is
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expressed by "years/4 - years/100 + years/400". To determine
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the number of leap years from current year to 1900, we subtract
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460 from the formula result. We do this since "days" is the
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number of days since 1900.
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*/
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static unsigned long __DaysToJan1( unsigned year )
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{
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unsigned years = 1900 + year - 1;
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unsigned leap_days = years / 4 - years / 100 + years / 400 - 460;
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return( year * 365UL + leap_days );
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}
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/* __brktime breaks down a calendar time (clock) into a struct tm t */
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struct tm *__brktime( unsigned long days,
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time_t wallclock,
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long gmtdelta, // localtime - gmtime
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struct tm *t )
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{
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unsigned long secs;
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unsigned year;
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int day_of_year;
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int month;
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short const *month_start;
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/*
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If date is Jan 1, 1970 0:00 to 12:00 UTC and we are west of UTC
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then add a day to wallclock, subtract the gmtdelta value, and
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decrement the calculated days. This prevents local times
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such as "Wed Dec 31 19:00:00 1969 (EST)" from being
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erroneously reported as "Sun Feb 6 01:28:16 2106 (EST)"
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since (wallclock - gmtdelta) wraps (i.e., wallclock < gmtdelta).
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*/
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if( wallclock < 12 * 60 * 60UL && gmtdelta > 0 )
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wallclock += SECONDS_PER_DAY, days--; /* days compensated for wallclock one day ahead */
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wallclock -= ( time_t ) gmtdelta;
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days += wallclock / SECONDS_PER_DAY;
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secs = wallclock % SECONDS_PER_DAY;
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t->tm_hour = ( int ) ( secs / 3600 ) ;
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secs = secs % 3600;
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t->tm_min = ( int ) ( secs / 60 );
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t->tm_sec = secs % 60;
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// The following two lines are not needed in the current implementation
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// because the range of values for days does not exceed DAYS_IN_400_YRS.
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// Even if it did, the algorithm still computes the correct values.
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//
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// unsigned year400s;
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//
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// year400s = (days / DAYS_IN_400_YRS) * 400;
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// days %= DAYS_IN_400_YRS;
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//
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// It is OK to reduce days to a value less than DAYS_IN_400_YRS, because
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// DAYS_IN_400_YRS is exactly divisible by 7. If it wasn't divisible by 7,
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// then the following line which appears at the bottom, should be computed
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// before the value of days is range reduced.
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// t->tm_wday = (days + 1) % 7; /* 24-sep-92 */
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//
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year = days / 365;
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day_of_year = ( int ) ( days - __DaysToJan1( year ) );
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while( day_of_year < 0 ) {
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--year;
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day_of_year += __leapyear( year + 1900 ) + 365;
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}
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// year += year400s;
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t->tm_yday = day_of_year;
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t->tm_year = ( int ) year;
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month_start = __diyr;
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if( __leapyear( year + 1900 ) )
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month_start = __dilyr;
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month = day_of_year / 31; /* approximate month */
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if( day_of_year >= month_start[month + 1] )
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++month;
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t->tm_mon = month;
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t->tm_mday = day_of_year - month_start[month] + 1;
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/* Calculate the day of the week */
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/* Jan 1,1900 is a Monday */
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t->tm_wday = ( days + 1 ) % 7; /* 24-sep-92 */
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return( t );
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}
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_WCRTLINK struct tm *_gmtime( const time_t *timer, struct tm *tm )
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{
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tm->tm_isdst = 0; /* assume not */
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return __brktime( DAYS_FROM_1900_TO_1970, *timer, 0L, tm );
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}
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_WCRTLINK struct tm *gmtime( const time_t *timer )
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{
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_INITTHETIME;
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return( _gmtime( timer, &_THE_TIME ) );
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}
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