summaryrefslogtreecommitdiffstats
path: root/exfat/libexfat/time.c
blob: 43c5fa4d9052bfb43949f6a13117230078ba330d (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
/*
	time.c (03.02.12)
	exFAT file system implementation library.

	Free exFAT implementation.
	Copyright (C) 2010-2013  Andrew Nayenko

	This program is free software; you can redistribute it and/or modify
	it under the terms of the GNU General Public License as published by
	the Free Software Foundation, either version 2 of the License, or
	(at your option) any later version.

	This program is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
	GNU General Public License for more details.

	You should have received a copy of the GNU General Public License along
	with this program; if not, write to the Free Software Foundation, Inc.,
	51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/

#include "exfat.h"

/* timezone offset from UTC in seconds; positive for western timezones,
   negative for eastern ones */
static long exfat_timezone;

#define SEC_IN_MIN 60ll
#define SEC_IN_HOUR (60 * SEC_IN_MIN)
#define SEC_IN_DAY (24 * SEC_IN_HOUR)
#define SEC_IN_YEAR (365 * SEC_IN_DAY) /* not leap year */
/* Unix epoch started at 0:00:00 UTC 1 January 1970 */
#define UNIX_EPOCH_YEAR 1970
/* exFAT epoch started at 0:00:00 UTC 1 January 1980 */
#define EXFAT_EPOCH_YEAR 1980
/* number of years from Unix epoch to exFAT epoch */
#define EPOCH_DIFF_YEAR (EXFAT_EPOCH_YEAR - UNIX_EPOCH_YEAR)
/* number of days from Unix epoch to exFAT epoch (considering leap days) */
#define EPOCH_DIFF_DAYS (EPOCH_DIFF_YEAR * 365 + EPOCH_DIFF_YEAR / 4)
/* number of seconds from Unix epoch to exFAT epoch (considering leap days) */
#define EPOCH_DIFF_SEC (EPOCH_DIFF_DAYS * SEC_IN_DAY)
/* number of leap years passed from exFAT epoch to the specified year
   (excluding the specified year itself) */
#define LEAP_YEARS(year) ((EXFAT_EPOCH_YEAR + (year) - 1) / 4 \
		- (EXFAT_EPOCH_YEAR - 1) / 4)
/* checks whether the specified year is leap */
#define IS_LEAP_YEAR(year) ((EXFAT_EPOCH_YEAR + (year)) % 4 == 0)

static const time_t days_in_year[] =
{
	/* Jan  Feb  Mar  Apr  May  Jun  Jul  Aug  Sep  Oct  Nov  Dec */
	0,   0,  31,  59,  90, 120, 151, 181, 212, 243, 273, 304, 334
};

time_t exfat_exfat2unix(le16_t date, le16_t time, uint8_t centisec)
{
	time_t unix_time = EPOCH_DIFF_SEC;
	uint16_t ndate = le16_to_cpu(date);
	uint16_t ntime = le16_to_cpu(time);

	uint16_t day    = ndate & 0x1f;      /* 5 bits, 1-31 */
	uint16_t month  = ndate >> 5 & 0xf;  /* 4 bits, 1-12 */
	uint16_t year   = ndate >> 9;        /* 7 bits, 1-127 (+1980) */

	uint16_t twosec = ntime & 0x1f;      /* 5 bits, 0-29 (2 sec granularity) */
	uint16_t min    = ntime >> 5 & 0x3f; /* 6 bits, 0-59 */
	uint16_t hour   = ntime >> 11;       /* 5 bits, 0-23 */

	if (day == 0 || month == 0 || month > 12)
	{
		exfat_error("bad date %u-%02hu-%02hu",
				year + EXFAT_EPOCH_YEAR, month, day);
		return 0;
	}
	if (hour > 23 || min > 59 || twosec > 29)
	{
		exfat_error("bad time %hu:%02hu:%02u",
				hour, min, twosec * 2);
		return 0;
	}
	if (centisec > 199)
	{
		exfat_error("bad centiseconds count %hhu", centisec);
		return 0;
	}

	/* every 4th year between 1904 and 2096 is leap */
	unix_time += year * SEC_IN_YEAR + LEAP_YEARS(year) * SEC_IN_DAY;
	unix_time += days_in_year[month] * SEC_IN_DAY;
	/* if it's leap year and February has passed we should add 1 day */
	if ((EXFAT_EPOCH_YEAR + year) % 4 == 0 && month > 2)
		unix_time += SEC_IN_DAY;
	unix_time += (day - 1) * SEC_IN_DAY;

	unix_time += hour * SEC_IN_HOUR;
	unix_time += min * SEC_IN_MIN;
	/* exFAT represents time with 2 sec granularity */
	unix_time += twosec * 2;
	unix_time += centisec / 100;

	/* exFAT stores timestamps in local time, so we correct it to UTC */
	unix_time += exfat_timezone;

	return unix_time;
}

void exfat_unix2exfat(time_t unix_time, le16_t* date, le16_t* time,
		uint8_t* centisec)
{
	time_t shift = EPOCH_DIFF_SEC + exfat_timezone;
	uint16_t day, month, year;
	uint16_t twosec, min, hour;
	int days;
	int i;

	/* time before exFAT epoch cannot be represented */
	if (unix_time < shift)
		unix_time = shift;

	unix_time -= shift;

	days = unix_time / SEC_IN_DAY;
	year = (4 * days) / (4 * 365 + 1);
	days -= year * 365 + LEAP_YEARS(year);
	month = 0;
	for (i = 1; i <= 12; i++)
	{
		int leap_day = (IS_LEAP_YEAR(year) && i == 2);
		int leap_sub = (IS_LEAP_YEAR(year) && i >= 3);

		if (i == 12 || days - leap_sub < days_in_year[i + 1] + leap_day)
		{
			month = i;
			days -= days_in_year[i] + leap_sub;
			break;
		}
	}
	day = days + 1;

	hour = (unix_time % SEC_IN_DAY) / SEC_IN_HOUR;
	min = (unix_time % SEC_IN_HOUR) / SEC_IN_MIN;
	twosec = (unix_time % SEC_IN_MIN) / 2;

	*date = cpu_to_le16(day | (month << 5) | (year << 9));
	*time = cpu_to_le16(twosec | (min << 5) | (hour << 11));
	if (centisec)
		*centisec = (unix_time % 2) * 100;
}

void exfat_tzset(void)
{
	time_t now;

	tzset();
	now = time(NULL);
	exfat_timezone = mktime(gmtime(&now)) - now;
}