compiler/stdc/gmtime_r.c

   1 /*
   2     Copyright © 1995-2012, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Convert a time into UTC, reentrant.
   6 */
   7
   8 /* At the moment no daylight saving time information
   9  * Implementation has to be changed when DST is implemented in AROS
  10  */
  11 static int __dstflag = -1;
  12
  13 static char monthtable[] =
  14 {
  15  /* JanFebMarAprMayJunJulAugSepOktNov */
  16     31,29,31,30,31,30,31,31,30,31,30
  17 };
  18
  19 /*****************************************************************************
  20
  21     NAME */
  22 #include <time.h>
  23
  24         struct tm * gmtime_r (
  25
  26 /*  SYNOPSIS */
  27         const time_t * tt,
  28         struct tm * tm)
  29
  30 /*  FUNCTION
  31         The gmtime_r() function converts the calendar time tt to
  32         broken-down time representation, expressed in Coordinated Universal
  33         Time (UTC).
  34
  35
  36     INPUTS
  37         tt - The time to convert
  38         tm - A struct tm to store the result in
  39
  40     RESULT
  41         The pointer passed in tm, containing the broken down time in
  42         Coordinated Universal Time (UTC).
  43
  44     NOTES
  45
  46     EXAMPLE
  47         time_t    tt;
  48         struct tm tm;
  49
  50         // Get the time
  51         time (&tt);
  52
  53         // and convert it
  54         gmtime (&tt, &tm);
  55
  56     BUGS
  57
  58     SEE ALSO
  59         time(), ctime_r(), asctime_r(), localtime_r()
  60
  61     INTERNALS
  62         Rules for leap-years:
  63
  64         1. every 4th year is a leap year
  65
  66         2. every 100th year is none
  67
  68         3. every 400th is one
  69
  70         4. 1900 was none, 2000 is one
  71
  72 ******************************************************************************/
  73 {
  74     signed long      tim;
  75     int              leapday  = 0,
  76                      leapyear = 0,
  77                      i;
  78
  79     tim = *tt;
  80
  81     tm->tm_sec = tim % 60;
  82     tim /= 60;
  83
  84     tm->tm_min = tim % 60;
  85     tim /= 60;
  86
  87     /*
  88         719162 number of days between 1.1.1 and 1.1.1970 if the calendar
  89         would go so far which it doesn't :-) this is true for all of the
  90         following.
  91     */
  92     tm->tm_hour = tim % 24;
  93     tim = tim / 24 + 719162;
  94
  95     tm->tm_wday = (tim + 1) % 7;
  96
  97     /* 146097 number of days from 1.1.1 to 1.1.401 */
  98     tm->tm_year = tim / 146097 * 400 - 1899;
  99     tim %= 146097;
 100
 101     /* 145731 number of days from 1.1.1 to 1.1.400 */
 102     if (tim >= 145731)
 103     {
 104         leapyear ++; /* The day is in one of the 400th */
 105
 106         /* Be careful: The last of the 4 centuries is 1 day longer */
 107         if (tim == 146096)
 108         {
 109             tim --;
 110             leapday ++;
 111         }
 112     }
 113
 114     /* 36524 number of days from 1.1.1 to 1.1.101 */
 115     tm->tm_year += tim / 36524 * 100;
 116     tim %= 36524;
 117
 118     /* 36159 number of days from 1.1.1 to 1.1.100 */
 119     if (tim >= 36159)
 120         leapyear --; /* The day is in one of the 100th */
 121
 122     /* 1461 number of days from 1.1.1 to 1.1.5 */
 123     tm->tm_year += tim / 1461 * 4;
 124     tim %= 1461;
 125
 126     /* 1095 number of days from 1.1.1 to 1.1.4 */
 127     if (tim >= 1095)
 128     {
 129         leapyear ++; /* The day is in one of the 4th */
 130
 131         /* Be careful: The 4th year is 1 day longer */
 132         if (tim == 1460)
 133         {
 134             tim --;
 135             leapday ++;
 136         }
 137     }
 138
 139     /* 365 days in a normal year */
 140     tm->tm_year += tim / 365;
 141     tim = tim % 365 + leapday;
 142
 143     tm->tm_yday = tim;
 144
 145     if (!leapyear && tim >= 31+28)
 146         tim ++; /* add 1 for 29-Feb if no leap year */
 147
 148     /* Find the month */
 149     for (i=0; i<11; i++)
 150     {
 151         if (tim < monthtable[i])
 152             break;
 153
 154         tim-=monthtable[i];
 155     }
 156
 157     tm->tm_mon = i;
 158     tm->tm_mday = tim + 1;
 159
 160     tm->tm_isdst = __dstflag;
 161
 162     return tm;
 163 } /* gmtime */