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165 lines
5.1 KiB
C
165 lines
5.1 KiB
C
/*
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time.c (03.02.12)
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exFAT file system implementation library.
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Free exFAT implementation.
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Copyright (C) 2010-2018 Andrew Nayenko
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 2 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License along
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with this program; if not, write to the Free Software Foundation, Inc.,
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51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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*/
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#include "exfat.h"
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/* timezone offset from UTC in seconds; positive for western timezones,
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negative for eastern ones */
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static long exfat_timezone;
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#define SEC_IN_MIN 60ll
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#define SEC_IN_HOUR (60 * SEC_IN_MIN)
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#define SEC_IN_DAY (24 * SEC_IN_HOUR)
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#define SEC_IN_YEAR (365 * SEC_IN_DAY) /* not leap year */
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/* Unix epoch started at 0:00:00 UTC 1 January 1970 */
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#define UNIX_EPOCH_YEAR 1970
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/* exFAT epoch started at 0:00:00 UTC 1 January 1980 */
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#define EXFAT_EPOCH_YEAR 1980
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/* number of years from Unix epoch to exFAT epoch */
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#define EPOCH_DIFF_YEAR (EXFAT_EPOCH_YEAR - UNIX_EPOCH_YEAR)
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/* number of days from Unix epoch to exFAT epoch (considering leap days) */
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#define EPOCH_DIFF_DAYS (EPOCH_DIFF_YEAR * 365 + EPOCH_DIFF_YEAR / 4)
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/* number of seconds from Unix epoch to exFAT epoch (considering leap days) */
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#define EPOCH_DIFF_SEC (EPOCH_DIFF_DAYS * SEC_IN_DAY)
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/* number of leap years passed from exFAT epoch to the specified year
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(excluding the specified year itself) */
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#define LEAP_YEARS(year) ((EXFAT_EPOCH_YEAR + (year) - 1) / 4 \
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- (EXFAT_EPOCH_YEAR - 1) / 4)
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/* checks whether the specified year is leap */
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#define IS_LEAP_YEAR(year) ((EXFAT_EPOCH_YEAR + (year)) % 4 == 0)
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static const time_t days_in_year[] =
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{
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/* Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec */
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0, 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334
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};
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time_t exfat_exfat2unix(le16_t date, le16_t time, uint8_t centisec)
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{
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time_t unix_time = EPOCH_DIFF_SEC;
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uint16_t ndate = le16_to_cpu(date);
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uint16_t ntime = le16_to_cpu(time);
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uint16_t day = ndate & 0x1f; /* 5 bits, 1-31 */
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uint16_t month = ndate >> 5 & 0xf; /* 4 bits, 1-12 */
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uint16_t year = ndate >> 9; /* 7 bits, 1-127 (+1980) */
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uint16_t twosec = ntime & 0x1f; /* 5 bits, 0-29 (2 sec granularity) */
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uint16_t min = ntime >> 5 & 0x3f; /* 6 bits, 0-59 */
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uint16_t hour = ntime >> 11; /* 5 bits, 0-23 */
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if (day == 0 || month == 0 || month > 12)
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{
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exfat_error("bad date %u-%02hu-%02hu",
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year + EXFAT_EPOCH_YEAR, month, day);
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return 0;
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}
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if (hour > 23 || min > 59 || twosec > 29)
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{
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exfat_error("bad time %hu:%02hu:%02u",
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hour, min, twosec * 2);
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return 0;
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}
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if (centisec > 199)
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{
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exfat_error("bad centiseconds count %hhu", centisec);
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return 0;
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}
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/* every 4th year between 1904 and 2096 is leap */
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unix_time += year * SEC_IN_YEAR + LEAP_YEARS(year) * SEC_IN_DAY;
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unix_time += days_in_year[month] * SEC_IN_DAY;
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/* if it's leap year and February has passed we should add 1 day */
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if ((EXFAT_EPOCH_YEAR + year) % 4 == 0 && month > 2)
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unix_time += SEC_IN_DAY;
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unix_time += (day - 1) * SEC_IN_DAY;
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unix_time += hour * SEC_IN_HOUR;
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unix_time += min * SEC_IN_MIN;
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/* exFAT represents time with 2 sec granularity */
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unix_time += twosec * 2;
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unix_time += centisec / 100;
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/* exFAT stores timestamps in local time, so we correct it to UTC */
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unix_time += exfat_timezone;
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return unix_time;
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}
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void exfat_unix2exfat(time_t unix_time, le16_t* date, le16_t* time,
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uint8_t* centisec)
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{
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time_t shift = EPOCH_DIFF_SEC + exfat_timezone;
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uint16_t day, month, year;
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uint16_t twosec, min, hour;
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int days;
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int i;
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/* time before exFAT epoch cannot be represented */
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if (unix_time < shift)
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unix_time = shift;
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unix_time -= shift;
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days = unix_time / SEC_IN_DAY;
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year = (4 * days) / (4 * 365 + 1);
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days -= year * 365 + LEAP_YEARS(year);
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month = 0;
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for (i = 1; i <= 12; i++)
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{
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int leap_day = (IS_LEAP_YEAR(year) && i == 2);
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int leap_sub = (IS_LEAP_YEAR(year) && i >= 3);
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if (i == 12 || days - leap_sub < days_in_year[i + 1] + leap_day)
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{
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month = i;
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days -= days_in_year[i] + leap_sub;
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break;
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}
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}
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day = days + 1;
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hour = (unix_time % SEC_IN_DAY) / SEC_IN_HOUR;
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min = (unix_time % SEC_IN_HOUR) / SEC_IN_MIN;
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twosec = (unix_time % SEC_IN_MIN) / 2;
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*date = cpu_to_le16(day | (month << 5) | (year << 9));
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*time = cpu_to_le16(twosec | (min << 5) | (hour << 11));
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if (centisec)
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*centisec = (unix_time % 2) * 100;
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}
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void exfat_tzset(void)
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{
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time_t now;
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struct tm* utc;
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tzset();
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now = time(NULL);
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utc = gmtime(&now);
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/* gmtime() always sets tm_isdst to 0 because daylight savings never
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affect UTC. Setting tm_isdst to -1 makes mktime() to determine whether
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summer time is in effect. */
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utc->tm_isdst = -1;
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exfat_timezone = mktime(utc) - now;
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}
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