1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause
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 * Convert MS-DOS FAT format timestamps to and from unix timespecs
29 *
30 * FAT filestamps originally consisted of two 16 bit integers, encoded like
31 * this:
32 *
33 * yyyyyyymmmmddddd (year - 1980, month, day)
34 *
35 * hhhhhmmmmmmsssss (hour, minutes, seconds divided by two)
36 *
37 * Subsequently even Microsoft realized that files could be accessed in less
38 * than two seconds and a byte was added containing:
39 *
40 * sfffffff (second mod two, 100ths of second)
41 *
42 * FAT timestamps are in the local timezone, with no indication of which
43 * timezone much less if daylight savings time applies.
44 *
45 * Later on again, in Windows NT, timestamps were defined relative to GMT.
46 *
47 * Purists will point out that UTC replaced GMT for such uses around
48 * half a century ago, already then. Ironically "NT" was an abbreviation of
49 * "New Technology". Anyway...
50 *
51 * The 'utc' argument determines if the resulting FATTIME timestamp
52 * should be on the UTC or local timezone calendar.
53 *
54 * The conversion functions below cut time into four-year leap-year
55 * cycles rather than single years and uses table lookups inside those
56 * cycles to get the months and years sorted out.
57 *
58 * Obviously we cannot calculate the correct table index going from
59 * a posix seconds count to Y/M/D, but we can get pretty close by
60 * dividing the daycount by 32 (giving a too low index), and then
61 * adjusting upwards a couple of steps if necessary.
62 *
63 * FAT timestamps have 7 bits for the year and starts at 1980, so
64 * they can represent up to 2107 which means that the non-leap-year
65 * 2100 must be handled.
66 */
67
68 #include <sys/param.h>
69 #include <sys/types.h>
70 #include <sys/time.h>
71 #include <sys/clock.h>
72
73 #ifdef TEST_DRIVER
74 /* stub for testing */
75 #define utc_offset() 0
76 #endif
77
78 #define DAY (24 * 60 * 60) /* Length of day in seconds */
79 #define YEAR 365 /* Length of normal year */
80 #define LYC (4 * YEAR + 1) /* Length of 4 year leap-year cycle */
81 #define T1980 (10 * 365 + 2) /* Days from 1970 to 1980 */
82 #define T2108 (138 * 365 + 33) /* Days from 1970 to 2108 */
83
84 /* End of month is N days from start of (normal) year */
85 #define JAN 31
86 #define FEB (JAN + 28)
87 #define MAR (FEB + 31)
88 #define APR (MAR + 30)
89 #define MAY (APR + 31)
90 #define JUN (MAY + 30)
91 #define JUL (JUN + 31)
92 #define AUG (JUL + 31)
93 #define SEP (AUG + 30)
94 #define OCT (SEP + 31)
95 #define NOV (OCT + 30)
96 #define DEC (NOV + 31)
97
98 /* Table of months in a 4 year leap-year cycle */
99
100 #define ENC(y,m) (((y) << 9) | ((m) << 5))
101
102 static const struct {
103 uint16_t days; /* month start in days relative to cycle */
104 uint16_t coded; /* encoded year + month information */
105 } mtab[48] = {
106 { 0 + 0 * YEAR, ENC(0, 1) },
107
108 { JAN + 0 * YEAR, ENC(0, 2) }, { FEB + 0 * YEAR + 1, ENC(0, 3) },
109 { MAR + 0 * YEAR + 1, ENC(0, 4) }, { APR + 0 * YEAR + 1, ENC(0, 5) },
110 { MAY + 0 * YEAR + 1, ENC(0, 6) }, { JUN + 0 * YEAR + 1, ENC(0, 7) },
111 { JUL + 0 * YEAR + 1, ENC(0, 8) }, { AUG + 0 * YEAR + 1, ENC(0, 9) },
112 { SEP + 0 * YEAR + 1, ENC(0, 10) }, { OCT + 0 * YEAR + 1, ENC(0, 11) },
113 { NOV + 0 * YEAR + 1, ENC(0, 12) }, { DEC + 0 * YEAR + 1, ENC(1, 1) },
114
115 { JAN + 1 * YEAR + 1, ENC(1, 2) }, { FEB + 1 * YEAR + 1, ENC(1, 3) },
116 { MAR + 1 * YEAR + 1, ENC(1, 4) }, { APR + 1 * YEAR + 1, ENC(1, 5) },
117 { MAY + 1 * YEAR + 1, ENC(1, 6) }, { JUN + 1 * YEAR + 1, ENC(1, 7) },
118 { JUL + 1 * YEAR + 1, ENC(1, 8) }, { AUG + 1 * YEAR + 1, ENC(1, 9) },
119 { SEP + 1 * YEAR + 1, ENC(1, 10) }, { OCT + 1 * YEAR + 1, ENC(1, 11) },
120 { NOV + 1 * YEAR + 1, ENC(1, 12) }, { DEC + 1 * YEAR + 1, ENC(2, 1) },
121
122 { JAN + 2 * YEAR + 1, ENC(2, 2) }, { FEB + 2 * YEAR + 1, ENC(2, 3) },
123 { MAR + 2 * YEAR + 1, ENC(2, 4) }, { APR + 2 * YEAR + 1, ENC(2, 5) },
124 { MAY + 2 * YEAR + 1, ENC(2, 6) }, { JUN + 2 * YEAR + 1, ENC(2, 7) },
125 { JUL + 2 * YEAR + 1, ENC(2, 8) }, { AUG + 2 * YEAR + 1, ENC(2, 9) },
126 { SEP + 2 * YEAR + 1, ENC(2, 10) }, { OCT + 2 * YEAR + 1, ENC(2, 11) },
127 { NOV + 2 * YEAR + 1, ENC(2, 12) }, { DEC + 2 * YEAR + 1, ENC(3, 1) },
128
129 { JAN + 3 * YEAR + 1, ENC(3, 2) }, { FEB + 3 * YEAR + 1, ENC(3, 3) },
130 { MAR + 3 * YEAR + 1, ENC(3, 4) }, { APR + 3 * YEAR + 1, ENC(3, 5) },
131 { MAY + 3 * YEAR + 1, ENC(3, 6) }, { JUN + 3 * YEAR + 1, ENC(3, 7) },
132 { JUL + 3 * YEAR + 1, ENC(3, 8) }, { AUG + 3 * YEAR + 1, ENC(3, 9) },
133 { SEP + 3 * YEAR + 1, ENC(3, 10) }, { OCT + 3 * YEAR + 1, ENC(3, 11) },
134 { NOV + 3 * YEAR + 1, ENC(3, 12) }
135 };
136
137 void
timespec2fattime(const struct timespec * tsp,int utc,uint16_t * ddp,uint16_t * dtp,uint8_t * dhp)138 timespec2fattime(const struct timespec *tsp, int utc, uint16_t *ddp,
139 uint16_t *dtp, uint8_t *dhp)
140 {
141 time_t t1;
142 unsigned t2, l, m;
143
144 t1 = tsp->tv_sec;
145 if (!utc)
146 t1 -= utc_offset();
147
148 if (dhp != NULL)
149 *dhp = (tsp->tv_sec & 1) * 100 + tsp->tv_nsec / 10000000;
150 if (dtp != NULL) {
151 *dtp = (t1 / 2) % 30;
152 *dtp |= ((t1 / 60) % 60) << 5;
153 *dtp |= ((t1 / 3600) % 24) << 11;
154 }
155 if (ddp != NULL) {
156 t2 = t1 / DAY;
157 if (t2 < T1980) {
158 /* Impossible date, truncate to 1980-01-01 */
159 *ddp = 0x0021;
160 } else {
161 t2 -= T1980;
162
163 /* 2100 is not a leap year */
164 if (t2 >= ((2100 - 1980) / 4 * LYC + FEB))
165 t2++;
166
167 /* Account for full leapyear cycles */
168 l = t2 / LYC;
169 *ddp = (l * 4) << 9;
170 t2 -= l * LYC;
171
172 /* Find approximate table entry */
173 m = t2 / 32;
174
175 /* Find correct table entry */
176 while (m < 47 && mtab[m + 1].days <= t2)
177 m++;
178
179 /* Get year + month from the table */
180 *ddp += mtab[m].coded;
181
182 /* And apply the day in the month */
183 t2 -= mtab[m].days - 1;
184 *ddp |= t2;
185 }
186 }
187 }
188
189 /*
190 * Table indexed by the bottom two bits of year + four bits of the month
191 * from the FAT timestamp, returning number of days into 4 year long
192 * leap-year cycle
193 */
194
195 #define DCOD(m, y, l) ((m) + YEAR * (y) + (l))
196 static const uint16_t daytab[64] = {
197 0, DCOD( 0, 0, 0), DCOD(JAN, 0, 0), DCOD(FEB, 0, 1),
198 DCOD(MAR, 0, 1), DCOD(APR, 0, 1), DCOD(MAY, 0, 1), DCOD(JUN, 0, 1),
199 DCOD(JUL, 0, 1), DCOD(AUG, 0, 1), DCOD(SEP, 0, 1), DCOD(OCT, 0, 1),
200 DCOD(NOV, 0, 1), DCOD(DEC, 0, 1), 0, 0,
201 0, DCOD( 0, 1, 1), DCOD(JAN, 1, 1), DCOD(FEB, 1, 1),
202 DCOD(MAR, 1, 1), DCOD(APR, 1, 1), DCOD(MAY, 1, 1), DCOD(JUN, 1, 1),
203 DCOD(JUL, 1, 1), DCOD(AUG, 1, 1), DCOD(SEP, 1, 1), DCOD(OCT, 1, 1),
204 DCOD(NOV, 1, 1), DCOD(DEC, 1, 1), 0, 0,
205 0, DCOD( 0, 2, 1), DCOD(JAN, 2, 1), DCOD(FEB, 2, 1),
206 DCOD(MAR, 2, 1), DCOD(APR, 2, 1), DCOD(MAY, 2, 1), DCOD(JUN, 2, 1),
207 DCOD(JUL, 2, 1), DCOD(AUG, 2, 1), DCOD(SEP, 2, 1), DCOD(OCT, 2, 1),
208 DCOD(NOV, 2, 1), DCOD(DEC, 2, 1), 0, 0,
209 0, DCOD( 0, 3, 1), DCOD(JAN, 3, 1), DCOD(FEB, 3, 1),
210 DCOD(MAR, 3, 1), DCOD(APR, 3, 1), DCOD(MAY, 3, 1), DCOD(JUN, 3, 1),
211 DCOD(JUL, 3, 1), DCOD(AUG, 3, 1), DCOD(SEP, 3, 1), DCOD(OCT, 3, 1),
212 DCOD(NOV, 3, 1), DCOD(DEC, 3, 1), 0, 0
213 };
214
215 void
fattime2timespec(unsigned dd,unsigned dt,unsigned dh,int utc,struct timespec * tsp)216 fattime2timespec(unsigned dd, unsigned dt, unsigned dh, int utc,
217 struct timespec *tsp)
218 {
219 unsigned day;
220
221 /* Unpack time fields */
222 tsp->tv_sec = (dt & 0x1f) << 1;
223 tsp->tv_sec += ((dt & 0x7e0) >> 5) * 60;
224 tsp->tv_sec += ((dt & 0xf800) >> 11) * 3600;
225 tsp->tv_sec += dh / 100;
226 tsp->tv_nsec = (dh % 100) * 10000000;
227
228 /* Day of month */
229 day = (dd & 0x1f) - 1;
230
231 /* Full leap-year cycles */
232 day += LYC * ((dd >> 11) & 0x1f);
233
234 /* Month offset from leap-year cycle */
235 day += daytab[(dd >> 5) & 0x3f];
236
237 /* 2100 is not a leap year */
238 if (day >= ((2100 - 1980) / 4 * LYC + FEB))
239 day--;
240
241 /* Align with time_t epoch */
242 day += T1980;
243
244 tsp->tv_sec += (time_t) DAY * day;
245 if (!utc)
246 tsp->tv_sec += utc_offset();
247 }
248
249 #ifdef TEST_DRIVER
250
251 #include <stdio.h>
252 #include <unistd.h>
253 #include <stdlib.h>
254
255 int
main(int argc __unused,char ** argv __unused)256 main(int argc __unused, char **argv __unused)
257 {
258 int i;
259 struct timespec ts;
260 struct tm tm;
261 double a;
262 uint16_t d, t;
263 uint8_t p;
264 char buf[100];
265
266 for (i = 0; i < 10000; i++) {
267 do {
268 /*
269 * 32-bits gets us to 2106-02-07 06:28:15, but we
270 * need to get to the end of 2107. So, we generate
271 * a 36-bit second count to get us way past 2106.
272 */
273 ts.tv_sec = ((time_t) arc4random() << 4) ^ arc4random();
274 } while ((ts.tv_sec < T1980 * 86400) || (ts.tv_sec >= T2108 * 86400ull));
275
276 ts.tv_nsec = random() % 1000000000;
277
278 printf("%10jd.%03ld -- ", (intmax_t) 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 timespec2fattime(&ts, 1, &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 fattime2timespec(d, t, p, 1, &ts);
298 printf("%10jd.%03ld == ", (intmax_t) 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