normal/datetime.c

   1 /* datetime.c - Module for common datetime function.  */
   2 /*
   3  *  GRUB  --  GRand Unified Bootloader
   4  *  Copyright (C) 2008  Free Software Foundation, Inc.
   5  *
   6  *  GRUB is free software: you can redistribute it and/or modify
   7  *  it under the terms of the GNU General Public License as published by
   8  *  the Free Software Foundation, either version 3 of the License, or
   9  *  (at your option) any later version.
  10  *
  11  *  GRUB is distributed in the hope that it will be useful,
  12  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  *  GNU General Public License for more details.
  15  *
  16  *  You should have received a copy of the GNU General Public License
  17  *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
  18  */
  19
  20 #include <grub/datetime.h>
  21
  22 static char *grub_weekday_names[] =
  23 {
  24   "Sunday",
  25   "Monday",
  26   "Tuesday",
  27   "Wednesday",
  28   "Thursday",
  29   "Friday",
  30   "Saturday",
  31 };
  32
  33 int
  34 grub_get_weekday (struct grub_datetime *datetime)
  35 {
  36   int a, y, m;
  37
  38   a = (14 - datetime->month) / 12;
  39   y = datetime->year - a;
  40   m = datetime->month + 12 * a - 2;
  41
  42   return (datetime->day + y + y / 4 - y / 100 + y / 400 + (31 * m / 12)) % 7;
  43 }
  44
  45 char *
  46 grub_get_weekday_name (struct grub_datetime *datetime)
  47 {
  48   return grub_weekday_names[grub_get_weekday (datetime)];
  49 }
  50
  51 #define SECPERMIN 60
  52 #define SECPERHOUR (60*SECPERMIN)
  53 #define SECPERDAY (24*SECPERHOUR)
  54 #define SECPERYEAR (365*SECPERDAY)
  55 #define SECPER4YEARS (4*SECPERYEAR+SECPERDAY)
  56
  57
  58 void
  59 grub_unixtime2datetime (grub_int32_t nix, struct grub_datetime *datetime)
  60 {
  61   int i;
  62   int div;
  63   grub_uint8_t months[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
  64   /* In the period of validity of unixtime all years divisible by 4
  65      are bissextile*/
  66   /* Convenience: let's have 3 consecutive non-bissextile years
  67      at the beginning of the epoch. So count from 1973 instead of 1970 */
  68   nix -= 3*SECPERYEAR + SECPERDAY;
  69   /* Transform C divisions and modulos to mathematical ones */
  70   div = nix / SECPER4YEARS;
  71   if (nix < 0)
  72     div--;
  73   datetime->year = 1973 + 4 * div;
  74   nix -= div * SECPER4YEARS;
  75
  76   /* On 31st December of bissextile years 365 days from the beginning
  77      of the year elapsed but year isn't finished yet */
  78   if (nix / SECPERYEAR == 4)
  79     {
  80       datetime->year += 3;
  81       nix -= 3*SECPERYEAR;
  82     }
  83   else
  84     {
  85       datetime->year += nix / SECPERYEAR;
  86       nix %= SECPERYEAR;
  87     }
  88   for (i = 0; i < 12
  89          && nix >= ((grub_int32_t) (i==1 && datetime->year % 4 == 0
  90                                     ? 29 : months[i]))*SECPERDAY; i++)
  91     nix -= ((grub_int32_t) (i==1 && datetime->year % 4 == 0
  92                             ? 29 : months[i]))*SECPERDAY;
  93   datetime->month = i + 1;
  94   datetime->day = 1 + (nix / SECPERDAY);
  95   nix %= SECPERDAY;
  96   datetime->hour = (nix / SECPERHOUR);
  97   nix %= SECPERHOUR;
  98   datetime->minute = nix / SECPERMIN;
  99   datetime->second = nix % SECPERMIN;
 100 }