libc/time/mktime.c

   1 /*
   2  *  ZeX/OS
   3  *  Copyright (C) 2009  Tomas 'ZeXx86' Jedrzejek (zexx86@zexos.org)
   4  *
   5  *  This program is free software: you can redistribute it and/or modify
   6  *  it under the terms of the GNU General Public License as published by
   7  *  the Free Software Foundation, either version 3 of the License, or
   8  *  (at your option) any later version.
   9  *
  10  *  This program is distributed in the hope that it will be useful,
  11  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  *  GNU General Public License for more details.
  14  *
  15  *  You should have received a copy of the GNU General Public License
  16  *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
  17  */
  18
  19
  20 #include <time.h>
  21
  22 #define MINUTE          60
  23 #define HOUR            (60 * MINUTE)
  24 #define DAY             (24 * HOUR)
  25 #define YEAR            (365 * DAY)
  26
  27 static int is_leap_year (int year)
  28 {
  29         if (year % 4 == 0) {
  30                 if (year % 100 == 0) {
  31                         if (year % 400 == 0)
  32                                 return 1;
  33                         else
  34                                 return 0;
  35                 }
  36
  37                 return 1;
  38         }
  39         return 0;
  40 }
  41
  42 static int count_leap_years (int epoch, int year)
  43 {
  44         int i, result = 0;
  45         for (i = epoch; i < year; i ++)
  46                 if (is_leap_year(i))
  47                         result ++;
  48
  49         return result;
  50 }
  51
  52 static int get_day (int year, int mon, int day)
  53 {
  54         int result;
  55
  56         switch (mon) {
  57                 case 0:
  58                         result = 0;
  59                         break;
  60                 case 1:
  61                         result = 31;
  62                         break; /* 1: 31 */
  63                 case 2:
  64                         result = 59;
  65                         break; /* 2: 31+28 */
  66                 case 3:
  67                         result = 90;
  68                         break; /* 3: 59+31 */
  69                 case 4:
  70                         result = 120;
  71                         break; /* 4: 90+30 */
  72                 case 5:
  73                         result = 151;
  74                         break; /* 5: 120+31 */
  75                 case 6:
  76                         result = 181;
  77                         break; /* 6: 151+30 */
  78                 case 7:
  79                         result = 212;
  80                         break; /* 7: 181+31 */
  81                 case 8:
  82                         result = 243;
  83                         break; /* 8: 212+31 */
  84                 case 9:
  85                         result = 273;
  86                         break; /* 9: 243+30 */
  87                 case 10:
  88                         result = 304;
  89                         break; /* 10: 273+31 */
  90                 case 11:
  91                         result = 334;
  92                         break; /* 11: 304+30 */
  93                 default:
  94                         break;
  95         }
  96
  97         if (is_leap_year (year) && mon > 2)
  98                 result ++;
  99
 100         result += day - 1;
 101
 102         return result;
 103 }
 104
 105 time_t mktime (struct tm *tm)
 106 {
 107         if (!tm)
 108                 return -1;
 109
 110         unsigned long result = 0;
 111
 112         result = tm->tm_sec;
 113         result += tm->tm_min * MINUTE;
 114         result += tm->tm_hour * HOUR;
 115         result += get_day (tm->tm_year, tm->tm_mon - 1, tm->tm_mday) * DAY;
 116         result += (tm->tm_year - EPOCH_YEAR) * YEAR;
 117         result += count_leap_years (EPOCH_YEAR, tm->tm_year) * DAY;
 118
 119         return result;
 120 }