compiler/clib/gmtime.c

   1 /*
   2     Copyright © 1995-2003, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Convert a time into UTC.
   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 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 (
  25
  26 /*  SYNOPSIS */
  27         const time_t * tt)
  28
  29 /*  FUNCTION
  30         The gmtime() function converts the calendar time tt to
  31         broken-down time representation, expressed in Coordinated Universal
  32         Time (UTC).
  33
  34
  35     INPUTS
  36         tt - The time to convert
  37
  38     RESULT
  39         The broken down time in Coordinated Universal Time (UTC).
  40
  41     NOTES
  42         This function must not be used in a shared library or
  43         in a threaded application.
  44
  45     EXAMPLE
  46         time_t      tt;
  47         struct tm * tm;
  48
  49         // Get the time
  50         time (&tt);
  51
  52         // and convert it
  53         tm = gmtime (&tt);
  54
  55     BUGS
  56
  57     SEE ALSO
  58         time(), ctime(), asctime(), localtime()
  59
  60     INTERNALS
  61         Rules for leap-years:
  62
  63         1. every 4th year is a leap year
  64
  65         2. every 100th year is none
  66
  67         3. every 400th is one
  68
  69         4. 1900 was none, 2000 is one
  70
  71 ******************************************************************************/
  72 {
  73     static struct tm utim;
  74     signed long      tim;
  75     int              leapday  = 0,
  76                      leapyear = 0,
  77                      i;
  78
  79     tim = *tt;
  80
  81     utim.tm_sec = tim % 60;
  82     tim /= 60;
  83
  84     utim.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     utim.tm_hour = tim % 24;
  93     tim = tim / 24 + 719162;
  94
  95     utim.tm_wday = (tim + 1) % 7;
  96
  97     /* 146097 number of days from 1.1.1 to 1.1.401 */
  98     utim.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     utim.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     utim.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     utim.tm_year += tim / 365;
 141     tim = tim % 365 + leapday;
 142
 143     utim.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     utim.tm_mon = i;
 158     utim.tm_mday = tim + 1;
 159
 160     utim.tm_isdst = __dstflag;
 161
 162     return &utim;
 163 } /* gmtime */