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
exfat_exfat2unix(le16_t date,le16_t time,uint8_t centisec)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
exfat_unix2exfat(time_t unix_time,le16_t * date,le16_t * time,uint8_t * centisec)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
exfat_tzset(void)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 }
165