compiler/stdc/mktime.c

   1 /*
   2     Copyright © 1995-2004, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Convert a broken-down time into calendar time.
   6 */
   7
   8
   9 static char monthtable[] =
  10 {
  11  /* JanFebMarAprMayJunJulAugSepOktNov */
  12     31,28,31,30,31,30,31,31,30,31,30
  13 };
  14
  15 /*****************************************************************************
  16
  17     NAME */
  18 #include <time.h>
  19
  20         time_t mktime (
  21
  22 /*  SYNOPSIS */
  23         struct tm * utim)
  24
  25 /*  FUNCTION
  26         The mktime() function converts the broken-down time utim to
  27         calendar time representation.
  28
  29     INPUTS
  30         utim - The broken-down time to convert
  31
  32     RESULT
  33         The converted calendar time
  34
  35     NOTES
  36
  37     EXAMPLE
  38         time_t      tt;
  39         struct tm * tm;
  40
  41         //Computation which results in a tm
  42         tm = ...
  43
  44         // and convert it
  45         tt = mktime (tm);
  46
  47     BUGS
  48         At the moment sanity check is not performed nor a normalization on the
  49         structure is done
  50
  51     SEE ALSO
  52         time(), ctime(), asctime(), localtime(), gmtime()
  53
  54     INTERNALS
  55         Rules for leap-years:
  56
  57         1. every 4th year is a leap year
  58
  59         2. every 100th year is none
  60
  61         3. every 400th is one
  62
  63         4. 1900 was none, 2000 is one
  64
  65 ******************************************************************************/
  66 {
  67     time_t           tt;
  68     int              leapyear,
  69                      days,
  70                      year,
  71                      i;
  72
  73     /* TODO: Add struct tm normalization code here */
  74
  75     /* Compute number of days in the years before this year and after 1970.
  76      * 1972 is the first leapyear
  77      */
  78     year = utim->tm_year-1;
  79     days = 365*(year-69) + (year-68)/4 - year/100 + (year+300)/400;
  80
  81     /* Add the day of the months before this month */
  82     for (i=0; i<utim->tm_mon; i++)
  83     {
  84         days += monthtable[i];
  85     }
  86
  87     /* Is this a leapyear ? */
  88     year = utim->tm_year;
  89     leapyear = year%4==0 && (year%100!=0 || (year+300)%400==0);
  90     if (leapyear && utim->tm_mon>1) days++;
  91
  92     /* Add day in the current month */
  93     days += utim->tm_mday - 1;
  94
  95     tt = ( (days*24+utim->tm_hour)*60 + utim->tm_min )*60 + utim->tm_sec;
  96
  97     return tt;
  98 } /* mktime */