xref: /freebsd/sys/kern/subr_fattime.c (revision e4f6a1bfa31a2299612bbf9dae402bb38d38b1df)
1 /*-
2  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
3  *
4  * Copyright (c) 2006 Poul-Henning Kamp
5  * All rights reserved.
6  *
7  * Redistribution and use in source and binary forms, with or without
8  * modification, are permitted provided that the following conditions
9  * are met:
10  * 1. Redistributions of source code must retain the above copyright
11  *    notice, this list of conditions and the following disclaimer.
12  * 2. Redistributions in binary form must reproduce the above copyright
13  *    notice, this list of conditions and the following disclaimer in the
14  *    documentation and/or other materials provided with the distribution.
15  *
16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
17  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
20  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
22  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
24  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26  * SUCH DAMAGE.
27  *
28  * $FreeBSD$
29  *
30  * Convert MS-DOS FAT format timestamps to and from unix timespecs
31  *
32  * FAT filestamps originally consisted of two 16 bit integers, encoded like
33  * this:
34  *
35  *	yyyyyyymmmmddddd (year - 1980, month, day)
36  *
37  *      hhhhhmmmmmmsssss (hour, minutes, seconds divided by two)
38  *
39  * Subsequently even Microsoft realized that files could be accessed in less
40  * than two seconds and a byte was added containing:
41  *
42  *      sfffffff	 (second mod two, 100ths of second)
43  *
44  * FAT timestamps are in the local timezone, with no indication of which
45  * timezone much less if daylight savings time applies.
46  *
47  * Later on again, in Windows NT, timestamps were defined relative to GMT.
48  *
49  * Purists will point out that UTC replaced GMT for such uses around
50  * half a century ago, already then.  Ironically "NT" was an abbreviation of
51  * "New Technology".  Anyway...
52  *
53  * The 'utc' argument determines if the resulting FATTIME timestamp
54  * should be on the UTC or local timezone calendar.
55  *
56  * The conversion functions below cut time into four-year leap-year
57  * cycles rather than single years and uses table lookups inside those
58  * cycles to get the months and years sorted out.
59  *
60  * Obviously we cannot calculate the correct table index going from
61  * a posix seconds count to Y/M/D, but we can get pretty close by
62  * dividing the daycount by 32 (giving a too low index), and then
63  * adjusting upwards a couple of steps if necessary.
64  *
65  * FAT timestamps have 7 bits for the year and starts at 1980, so
66  * they can represent up to 2107 which means that the non-leap-year
67  * 2100 must be handled.
68  *
69  * XXX: As long as time_t is 32 bits this is not relevant or easily
70  * XXX: testable.  Revisit when time_t grows bigger.
71  * XXX: grepfodder: 64 bit time_t, y2100, y2.1k, 2100, leap year
72  *
73  */
74 
75 #include <sys/param.h>
76 #include <sys/types.h>
77 #include <sys/time.h>
78 #include <sys/clock.h>
79 
80 #define DAY	(24 * 60 * 60)	/* Length of day in seconds */
81 #define YEAR	365		/* Length of normal year */
82 #define LYC	(4 * YEAR + 1)	/* Length of 4 year leap-year cycle */
83 #define T1980	(10 * 365 + 2)	/* Days from 1970 to 1980 */
84 
85 /* End of month is N days from start of (normal) year */
86 #define JAN	31
87 #define FEB	(JAN + 28)
88 #define MAR	(FEB + 31)
89 #define APR	(MAR + 30)
90 #define MAY	(APR + 31)
91 #define JUN	(MAY + 30)
92 #define JUL	(JUN + 31)
93 #define AUG	(JUL + 31)
94 #define SEP	(AUG + 30)
95 #define OCT	(SEP + 31)
96 #define NOV	(OCT + 30)
97 #define DEC	(NOV + 31)
98 
99 /* Table of months in a 4 year leap-year cycle */
100 
101 #define ENC(y,m)	(((y) << 9) | ((m) << 5))
102 
103 static const struct {
104 	uint16_t	days;	/* month start in days relative to cycle */
105 	uint16_t	coded;	/* encoded year + month information */
106 } mtab[48] = {
107 	{   0 + 0 * YEAR,     ENC(0, 1)  },
108 
109 	{ JAN + 0 * YEAR,     ENC(0, 2)  }, { FEB + 0 * YEAR + 1, ENC(0, 3)  },
110 	{ MAR + 0 * YEAR + 1, ENC(0, 4)  }, { APR + 0 * YEAR + 1, ENC(0, 5)  },
111 	{ MAY + 0 * YEAR + 1, ENC(0, 6)  }, { JUN + 0 * YEAR + 1, ENC(0, 7)  },
112 	{ JUL + 0 * YEAR + 1, ENC(0, 8)  }, { AUG + 0 * YEAR + 1, ENC(0, 9)  },
113 	{ SEP + 0 * YEAR + 1, ENC(0, 10) }, { OCT + 0 * YEAR + 1, ENC(0, 11) },
114 	{ NOV + 0 * YEAR + 1, ENC(0, 12) }, { DEC + 0 * YEAR + 1, ENC(1, 1)  },
115 
116 	{ JAN + 1 * YEAR + 1, ENC(1, 2)  }, { FEB + 1 * YEAR + 1, ENC(1, 3)  },
117 	{ MAR + 1 * YEAR + 1, ENC(1, 4)  }, { APR + 1 * YEAR + 1, ENC(1, 5)  },
118 	{ MAY + 1 * YEAR + 1, ENC(1, 6)  }, { JUN + 1 * YEAR + 1, ENC(1, 7)  },
119 	{ JUL + 1 * YEAR + 1, ENC(1, 8)  }, { AUG + 1 * YEAR + 1, ENC(1, 9)  },
120 	{ SEP + 1 * YEAR + 1, ENC(1, 10) }, { OCT + 1 * YEAR + 1, ENC(1, 11) },
121 	{ NOV + 1 * YEAR + 1, ENC(1, 12) }, { DEC + 1 * YEAR + 1, ENC(2, 1)  },
122 
123 	{ JAN + 2 * YEAR + 1, ENC(2, 2)  }, { FEB + 2 * YEAR + 1, ENC(2, 3)  },
124 	{ MAR + 2 * YEAR + 1, ENC(2, 4)  }, { APR + 2 * YEAR + 1, ENC(2, 5)  },
125 	{ MAY + 2 * YEAR + 1, ENC(2, 6)  }, { JUN + 2 * YEAR + 1, ENC(2, 7)  },
126 	{ JUL + 2 * YEAR + 1, ENC(2, 8)  }, { AUG + 2 * YEAR + 1, ENC(2, 9)  },
127 	{ SEP + 2 * YEAR + 1, ENC(2, 10) }, { OCT + 2 * YEAR + 1, ENC(2, 11) },
128 	{ NOV + 2 * YEAR + 1, ENC(2, 12) }, { DEC + 2 * YEAR + 1, ENC(3, 1)  },
129 
130 	{ JAN + 3 * YEAR + 1, ENC(3, 2)  }, { FEB + 3 * YEAR + 1, ENC(3, 3)  },
131 	{ MAR + 3 * YEAR + 1, ENC(3, 4)  }, { APR + 3 * YEAR + 1, ENC(3, 5)  },
132 	{ MAY + 3 * YEAR + 1, ENC(3, 6)  }, { JUN + 3 * YEAR + 1, ENC(3, 7)  },
133 	{ JUL + 3 * YEAR + 1, ENC(3, 8)  }, { AUG + 3 * YEAR + 1, ENC(3, 9)  },
134 	{ SEP + 3 * YEAR + 1, ENC(3, 10) }, { OCT + 3 * YEAR + 1, ENC(3, 11) },
135 	{ NOV + 3 * YEAR + 1, ENC(3, 12) }
136 };
137 
138 
139 void
140 timespec2fattime(struct timespec *tsp, int utc, uint16_t *ddp, uint16_t *dtp, uint8_t *dhp)
141 {
142 	time_t t1;
143 	unsigned t2, l, m;
144 
145 	t1 = tsp->tv_sec;
146 	if (!utc)
147 		t1 -= utc_offset();
148 
149 	if (dhp != NULL)
150 		*dhp = (tsp->tv_sec & 1) * 100 + tsp->tv_nsec / 10000000;
151 	if (dtp != NULL) {
152 		*dtp = (t1 / 2) % 30;
153 		*dtp |= ((t1 / 60) % 60) << 5;
154 		*dtp |= ((t1 / 3600) % 24) << 11;
155 	}
156 	if (ddp != NULL) {
157 		t2 = t1 / DAY;
158 		if (t2 < T1980) {
159 			/* Impossible date, truncate to 1980-01-01 */
160 			*ddp = 0x0021;
161 		} else {
162 			t2 -= T1980;
163 
164 			/*
165 			 * 2100 is not a leap year.
166 			 * XXX: a 32 bit time_t can not get us here.
167 			 */
168 			if (t2 >= ((2100 - 1980) / 4 * LYC + FEB))
169 				t2++;
170 
171 			/* Account for full leapyear cycles */
172 			l = t2 / LYC;
173 			*ddp = (l * 4) << 9;
174 			t2 -= l * LYC;
175 
176 			/* Find approximate table entry */
177 			m = t2 / 32;
178 
179 			/* Find correct table entry */
180 			while (m < 47 && mtab[m + 1].days <= t2)
181 				m++;
182 
183 			/* Get year + month from the table */
184 			*ddp += mtab[m].coded;
185 
186 			/* And apply the day in the month */
187 			t2 -= mtab[m].days - 1;
188 			*ddp |= t2;
189 		}
190 	}
191 }
192 
193 /*
194  * Table indexed by the bottom two bits of year + four bits of the month
195  * from the FAT timestamp, returning number of days into 4 year long
196  * leap-year cycle
197  */
198 
199 #define DCOD(m, y, l)	((m) + YEAR * (y) + (l))
200 static const uint16_t daytab[64] = {
201 	0, 		 DCOD(  0, 0, 0), DCOD(JAN, 0, 0), DCOD(FEB, 0, 1),
202 	DCOD(MAR, 0, 1), DCOD(APR, 0, 1), DCOD(MAY, 0, 1), DCOD(JUN, 0, 1),
203 	DCOD(JUL, 0, 1), DCOD(AUG, 0, 1), DCOD(SEP, 0, 1), DCOD(OCT, 0, 1),
204 	DCOD(NOV, 0, 1), DCOD(DEC, 0, 1), 0,               0,
205 	0, 		 DCOD(  0, 1, 1), DCOD(JAN, 1, 1), DCOD(FEB, 1, 1),
206 	DCOD(MAR, 1, 1), DCOD(APR, 1, 1), DCOD(MAY, 1, 1), DCOD(JUN, 1, 1),
207 	DCOD(JUL, 1, 1), DCOD(AUG, 1, 1), DCOD(SEP, 1, 1), DCOD(OCT, 1, 1),
208 	DCOD(NOV, 1, 1), DCOD(DEC, 1, 1), 0,               0,
209 	0,		 DCOD(  0, 2, 1), DCOD(JAN, 2, 1), DCOD(FEB, 2, 1),
210 	DCOD(MAR, 2, 1), DCOD(APR, 2, 1), DCOD(MAY, 2, 1), DCOD(JUN, 2, 1),
211 	DCOD(JUL, 2, 1), DCOD(AUG, 2, 1), DCOD(SEP, 2, 1), DCOD(OCT, 2, 1),
212 	DCOD(NOV, 2, 1), DCOD(DEC, 2, 1), 0,               0,
213 	0,		 DCOD(  0, 3, 1), DCOD(JAN, 3, 1), DCOD(FEB, 3, 1),
214 	DCOD(MAR, 3, 1), DCOD(APR, 3, 1), DCOD(MAY, 3, 1), DCOD(JUN, 3, 1),
215 	DCOD(JUL, 3, 1), DCOD(AUG, 3, 1), DCOD(SEP, 3, 1), DCOD(OCT, 3, 1),
216 	DCOD(NOV, 3, 1), DCOD(DEC, 3, 1), 0,               0
217 };
218 
219 void
220 fattime2timespec(unsigned dd, unsigned dt, unsigned dh, int utc, struct timespec *tsp)
221 {
222 	unsigned day;
223 
224 	/* Unpack time fields */
225 	tsp->tv_sec = (dt & 0x1f) << 1;
226 	tsp->tv_sec += ((dt & 0x7e0) >> 5) * 60;
227 	tsp->tv_sec += ((dt & 0xf800) >> 11) * 3600;
228 	tsp->tv_sec += dh / 100;
229 	tsp->tv_nsec = (dh % 100) * 10000000;
230 
231 	/* Day of month */
232 	day = (dd & 0x1f) - 1;
233 
234 	/* Full leap-year cycles */
235 	day += LYC * ((dd >> 11) & 0x1f);
236 
237 	/* Month offset from leap-year cycle */
238 	day += daytab[(dd >> 5) & 0x3f];
239 
240 	/*
241 	 * 2100 is not a leap year.
242 	 * XXX: a 32 bit time_t can not get us here.
243 	 */
244 	if (day >= ((2100 - 1980) / 4 * LYC + FEB))
245 		day--;
246 
247 	/* Align with time_t epoch */
248 	day += T1980;
249 
250 	tsp->tv_sec += DAY * day;
251 	if (!utc)
252 		tsp->tv_sec += utc_offset();
253 }
254 
255 #ifdef TEST_DRIVER
256 
257 #include <stdio.h>
258 #include <unistd.h>
259 #include <stdlib.h>
260 
261 int
262 main(int argc __unused, char **argv __unused)
263 {
264 	int i;
265 	struct timespec ts;
266 	struct tm tm;
267 	double a;
268 	uint16_t d, t;
269 	uint8_t p;
270 	char buf[100];
271 
272 	for (i = 0; i < 10000; i++) {
273 		do {
274 			ts.tv_sec = random();
275 		} while (ts.tv_sec < T1980 * 86400);
276 		ts.tv_nsec = random() % 1000000000;
277 
278 		printf("%10d.%03ld -- ", ts.tv_sec, ts.tv_nsec / 1000000);
279 
280 		gmtime_r(&ts.tv_sec, &tm);
281 		strftime(buf, sizeof buf, "%Y %m %d %H %M %S", &tm);
282 		printf("%s -- ", buf);
283 
284 		a = ts.tv_sec + ts.tv_nsec * 1e-9;
285 		d = t = p = 0;
286 		timet2fattime(&ts, &d, &t, &p);
287 		printf("%04x %04x %02x -- ", d, t, p);
288 		printf("%3d %02d %02d %02d %02d %02d -- ",
289 		    ((d >> 9)  & 0x7f) + 1980,
290 		    (d >> 5)  & 0x0f,
291 		    (d >> 0)  & 0x1f,
292 		    (t >> 11) & 0x1f,
293 		    (t >> 5)  & 0x3f,
294 		    ((t >> 0)  & 0x1f) * 2);
295 
296 		ts.tv_sec = ts.tv_nsec = 0;
297 		fattime2timet(d, t, p, &ts);
298 		printf("%10d.%03ld == ", ts.tv_sec, ts.tv_nsec / 1000000);
299 		gmtime_r(&ts.tv_sec, &tm);
300 		strftime(buf, sizeof buf, "%Y %m %d %H %M %S", &tm);
301 		printf("%s -- ", buf);
302 		a -= ts.tv_sec + ts.tv_nsec * 1e-9;
303 		printf("%.3f", a);
304 		printf("\n");
305 	}
306 	return (0);
307 }
308 
309 #endif /* TEST_DRIVER */
310