LinuxGUI/Ventoy2Disk/Lib/exfat/src/libexfat/time.c

   1 /*
   2         time.c (03.02.12)
   3         exFAT file system implementation library.
   4
   5         Free exFAT implementation.
   6         Copyright (C) 2010-2018  Andrew Nayenko
   7
   8         This program is free software; you can redistribute it and/or modify
   9         it under the terms of the GNU General Public License as published by
  10         the Free Software Foundation, either version 2 of the License, or
  11         (at your option) any later version.
  12
  13         This program is distributed in the hope that it will be useful,
  14         but WITHOUT ANY WARRANTY; without even the implied warranty of
  15         MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16         GNU General Public License for more details.
  17
  18         You should have received a copy of the GNU General Public License along
  19         with this program; if not, write to the Free Software Foundation, Inc.,
  20         51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  21 */
  22
  23 #include "exfat.h"
  24
  25 /* timezone offset from UTC in seconds; positive for western timezones,
  26    negative for eastern ones */
  27 static long exfat_timezone;
  28
  29 #define SEC_IN_MIN 60ll
  30 #define SEC_IN_HOUR (60 * SEC_IN_MIN)
  31 #define SEC_IN_DAY (24 * SEC_IN_HOUR)
  32 #define SEC_IN_YEAR (365 * SEC_IN_DAY) /* not leap year */
  33 /* Unix epoch started at 0:00:00 UTC 1 January 1970 */
  34 #define UNIX_EPOCH_YEAR 1970
  35 /* exFAT epoch started at 0:00:00 UTC 1 January 1980 */
  36 #define EXFAT_EPOCH_YEAR 1980
  37 /* number of years from Unix epoch to exFAT epoch */
  38 #define EPOCH_DIFF_YEAR (EXFAT_EPOCH_YEAR - UNIX_EPOCH_YEAR)
  39 /* number of days from Unix epoch to exFAT epoch (considering leap days) */
  40 #define EPOCH_DIFF_DAYS (EPOCH_DIFF_YEAR * 365 + EPOCH_DIFF_YEAR / 4)
  41 /* number of seconds from Unix epoch to exFAT epoch (considering leap days) */
  42 #define EPOCH_DIFF_SEC (EPOCH_DIFF_DAYS * SEC_IN_DAY)
  43 /* number of leap years passed from exFAT epoch to the specified year
  44    (excluding the specified year itself) */
  45 #define LEAP_YEARS(year) ((EXFAT_EPOCH_YEAR + (year) - 1) / 4 \
  46                 - (EXFAT_EPOCH_YEAR - 1) / 4)
  47 /* checks whether the specified year is leap */
  48 #define IS_LEAP_YEAR(year) ((EXFAT_EPOCH_YEAR + (year)) % 4 == 0)
  49
  50 static const time_t days_in_year[] =
  51 {
  52         /* Jan  Feb  Mar  Apr  May  Jun  Jul  Aug  Sep  Oct  Nov  Dec */
  53         0,   0,  31,  59,  90, 120, 151, 181, 212, 243, 273, 304, 334
  54 };
  55
  56 time_t exfat_exfat2unix(le16_t date, le16_t time, uint8_t centisec)
  57 {
  58         time_t unix_time = EPOCH_DIFF_SEC;
  59         uint16_t ndate = le16_to_cpu(date);
  60         uint16_t ntime = le16_to_cpu(time);
  61
  62         uint16_t day    = ndate & 0x1f;      /* 5 bits, 1-31 */
  63         uint16_t month  = ndate >> 5 & 0xf;  /* 4 bits, 1-12 */
  64         uint16_t year   = ndate >> 9;        /* 7 bits, 1-127 (+1980) */
  65
  66         uint16_t twosec = ntime & 0x1f;      /* 5 bits, 0-29 (2 sec granularity) */
  67         uint16_t min    = ntime >> 5 & 0x3f; /* 6 bits, 0-59 */
  68         uint16_t hour   = ntime >> 11;       /* 5 bits, 0-23 */
  69
  70         if (day == 0 || month == 0 || month > 12)
  71         {
  72                 exfat_error("bad date %u-%02hu-%02hu",
  73                                 year + EXFAT_EPOCH_YEAR, month, day);
  74                 return 0;
  75         }
  76         if (hour > 23 || min > 59 || twosec > 29)
  77         {
  78                 exfat_error("bad time %hu:%02hu:%02u",
  79                                 hour, min, twosec * 2);
  80                 return 0;
  81         }
  82         if (centisec > 199)
  83         {
  84                 exfat_error("bad centiseconds count %hhu", centisec);
  85                 return 0;
  86         }
  87
  88         /* every 4th year between 1904 and 2096 is leap */
  89         unix_time += year * SEC_IN_YEAR + LEAP_YEARS(year) * SEC_IN_DAY;
  90         unix_time += days_in_year[month] * SEC_IN_DAY;
  91         /* if it's leap year and February has passed we should add 1 day */
  92         if ((EXFAT_EPOCH_YEAR + year) % 4 == 0 && month > 2)
  93                 unix_time += SEC_IN_DAY;
  94         unix_time += (day - 1) * SEC_IN_DAY;
  95
  96         unix_time += hour * SEC_IN_HOUR;
  97         unix_time += min * SEC_IN_MIN;
  98         /* exFAT represents time with 2 sec granularity */
  99         unix_time += twosec * 2;
 100         unix_time += centisec / 100;
 101
 102         /* exFAT stores timestamps in local time, so we correct it to UTC */
 103         unix_time += exfat_timezone;
 104
 105         return unix_time;
 106 }
 107
 108 void exfat_unix2exfat(time_t unix_time, le16_t* date, le16_t* time,
 109                 uint8_t* centisec)
 110 {
 111         time_t shift = EPOCH_DIFF_SEC + exfat_timezone;
 112         uint16_t day, month, year;
 113         uint16_t twosec, min, hour;
 114         int days;
 115         int i;
 116
 117         /* time before exFAT epoch cannot be represented */
 118         if (unix_time < shift)
 119                 unix_time = shift;
 120
 121         unix_time -= shift;
 122
 123         days = unix_time / SEC_IN_DAY;
 124         year = (4 * days) / (4 * 365 + 1);
 125         days -= year * 365 + LEAP_YEARS(year);
 126         month = 0;
 127         for (i = 1; i <= 12; i++)
 128         {
 129                 int leap_day = (IS_LEAP_YEAR(year) && i == 2);
 130                 int leap_sub = (IS_LEAP_YEAR(year) && i >= 3);
 131
 132                 if (i == 12 || days - leap_sub < days_in_year[i + 1] + leap_day)
 133                 {
 134                         month = i;
 135                         days -= days_in_year[i] + leap_sub;
 136                         break;
 137                 }
 138         }
 139         day = days + 1;
 140
 141         hour = (unix_time % SEC_IN_DAY) / SEC_IN_HOUR;
 142         min = (unix_time % SEC_IN_HOUR) / SEC_IN_MIN;
 143         twosec = (unix_time % SEC_IN_MIN) / 2;
 144
 145         *date = cpu_to_le16(day | (month << 5) | (year << 9));
 146         *time = cpu_to_le16(twosec | (min << 5) | (hour << 11));
 147         if (centisec)
 148                 *centisec = (unix_time % 2) * 100;
 149 }
 150
 151 void exfat_tzset(void)
 152 {
 153         time_t now;
 154         struct tm* utc;
 155
 156         tzset();
 157         now = time(NULL);
 158         utc = gmtime(&now);
 159         /* gmtime() always sets tm_isdst to 0 because daylight savings never
 160            affect UTC. Setting tm_isdst to -1 makes mktime() to determine whether
 161            summer time is in effect. */
 162         utc->tm_isdst = -1;
 163         exfat_timezone = mktime(utc) - now;
 164 }