1 /*-
2 * Copyright (c) 2006 Poul-Henning Kamp
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24 * SUCH DAMAGE.
25 *
26 * $FreeBSD$
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 * XXX: As long as time_t is 32 bits this is not relevant or easily
68 * XXX: testable. Revisit when time_t grows bigger.
69 * XXX: grepfodder: 64 bit time_t, y2100, y2.1k, 2100, leap year
70 *
71 */
72
73 #include <sys/param.h>
74 #include <sys/types.h>
75 #include <sys/time.h>
76 #include <sys/clock.h>
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
83 /* End of month is N days from start of (normal) year */
84 #define JAN 31
85 #define FEB (JAN + 28)
86 #define MAR (FEB + 31)
87 #define APR (MAR + 30)
88 #define MAY (APR + 31)
89 #define JUN (MAY + 30)
90 #define JUL (JUN + 31)
91 #define AUG (JUL + 31)
92 #define SEP (AUG + 30)
93 #define OCT (SEP + 31)
94 #define NOV (OCT + 30)
95 #define DEC (NOV + 31)
96
97 /* Table of months in a 4 year leap-year cycle */
98
99 #define ENC(y,m) (((y) << 9) | ((m) << 5))
100
101 static const struct {
102 uint16_t days; /* month start in days relative to cycle */
103 uint16_t coded; /* encoded year + month information */
104 } mtab[48] = {
105 { 0 + 0 * YEAR, ENC(0, 1) },
106
107 { JAN + 0 * YEAR, ENC(0, 2) }, { FEB + 0 * YEAR + 1, ENC(0, 3) },
108 { MAR + 0 * YEAR + 1, ENC(0, 4) }, { APR + 0 * YEAR + 1, ENC(0, 5) },
109 { MAY + 0 * YEAR + 1, ENC(0, 6) }, { JUN + 0 * YEAR + 1, ENC(0, 7) },
110 { JUL + 0 * YEAR + 1, ENC(0, 8) }, { AUG + 0 * YEAR + 1, ENC(0, 9) },
111 { SEP + 0 * YEAR + 1, ENC(0, 10) }, { OCT + 0 * YEAR + 1, ENC(0, 11) },
112 { NOV + 0 * YEAR + 1, ENC(0, 12) }, { DEC + 0 * YEAR + 1, ENC(1, 1) },
113
114 { JAN + 1 * YEAR + 1, ENC(1, 2) }, { FEB + 1 * YEAR + 1, ENC(1, 3) },
115 { MAR + 1 * YEAR + 1, ENC(1, 4) }, { APR + 1 * YEAR + 1, ENC(1, 5) },
116 { MAY + 1 * YEAR + 1, ENC(1, 6) }, { JUN + 1 * YEAR + 1, ENC(1, 7) },
117 { JUL + 1 * YEAR + 1, ENC(1, 8) }, { AUG + 1 * YEAR + 1, ENC(1, 9) },
118 { SEP + 1 * YEAR + 1, ENC(1, 10) }, { OCT + 1 * YEAR + 1, ENC(1, 11) },
119 { NOV + 1 * YEAR + 1, ENC(1, 12) }, { DEC + 1 * YEAR + 1, ENC(2, 1) },
120
121 { JAN + 2 * YEAR + 1, ENC(2, 2) }, { FEB + 2 * YEAR + 1, ENC(2, 3) },
122 { MAR + 2 * YEAR + 1, ENC(2, 4) }, { APR + 2 * YEAR + 1, ENC(2, 5) },
123 { MAY + 2 * YEAR + 1, ENC(2, 6) }, { JUN + 2 * YEAR + 1, ENC(2, 7) },
124 { JUL + 2 * YEAR + 1, ENC(2, 8) }, { AUG + 2 * YEAR + 1, ENC(2, 9) },
125 { SEP + 2 * YEAR + 1, ENC(2, 10) }, { OCT + 2 * YEAR + 1, ENC(2, 11) },
126 { NOV + 2 * YEAR + 1, ENC(2, 12) }, { DEC + 2 * YEAR + 1, ENC(3, 1) },
127
128 { JAN + 3 * YEAR + 1, ENC(3, 2) }, { FEB + 3 * YEAR + 1, ENC(3, 3) },
129 { MAR + 3 * YEAR + 1, ENC(3, 4) }, { APR + 3 * YEAR + 1, ENC(3, 5) },
130 { MAY + 3 * YEAR + 1, ENC(3, 6) }, { JUN + 3 * YEAR + 1, ENC(3, 7) },
131 { JUL + 3 * YEAR + 1, ENC(3, 8) }, { AUG + 3 * YEAR + 1, ENC(3, 9) },
132 { SEP + 3 * YEAR + 1, ENC(3, 10) }, { OCT + 3 * YEAR + 1, ENC(3, 11) },
133 { NOV + 3 * YEAR + 1, ENC(3, 12) }
134 };
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 /*
164 * 2100 is not a leap year.
165 * XXX: a 32 bit time_t can not get us here.
166 */
167 if (t2 >= ((2100 - 1980) / 4 * LYC + FEB))
168 t2++;
169
170 /* Account for full leapyear cycles */
171 l = t2 / LYC;
172 *ddp = (l * 4) << 9;
173 t2 -= l * LYC;
174
175 /* Find approximate table entry */
176 m = t2 / 32;
177
178 /* Find correct table entry */
179 while (m < 47 && mtab[m + 1].days <= t2)
180 m++;
181
182 /* Get year + month from the table */
183 *ddp += mtab[m].coded;
184
185 /* And apply the day in the month */
186 t2 -= mtab[m].days - 1;
187 *ddp |= t2;
188 }
189 }
190 }
191
192 /*
193 * Table indexed by the bottom two bits of year + four bits of the month
194 * from the FAT timestamp, returning number of days into 4 year long
195 * leap-year cycle
196 */
197
198 #define DCOD(m, y, l) ((m) + YEAR * (y) + (l))
199 static const uint16_t daytab[64] = {
200 0, DCOD( 0, 0, 0), DCOD(JAN, 0, 0), DCOD(FEB, 0, 1),
201 DCOD(MAR, 0, 1), DCOD(APR, 0, 1), DCOD(MAY, 0, 1), DCOD(JUN, 0, 1),
202 DCOD(JUL, 0, 1), DCOD(AUG, 0, 1), DCOD(SEP, 0, 1), DCOD(OCT, 0, 1),
203 DCOD(NOV, 0, 1), DCOD(DEC, 0, 1), 0, 0,
204 0, DCOD( 0, 1, 1), DCOD(JAN, 1, 1), DCOD(FEB, 1, 1),
205 DCOD(MAR, 1, 1), DCOD(APR, 1, 1), DCOD(MAY, 1, 1), DCOD(JUN, 1, 1),
206 DCOD(JUL, 1, 1), DCOD(AUG, 1, 1), DCOD(SEP, 1, 1), DCOD(OCT, 1, 1),
207 DCOD(NOV, 1, 1), DCOD(DEC, 1, 1), 0, 0,
208 0, DCOD( 0, 2, 1), DCOD(JAN, 2, 1), DCOD(FEB, 2, 1),
209 DCOD(MAR, 2, 1), DCOD(APR, 2, 1), DCOD(MAY, 2, 1), DCOD(JUN, 2, 1),
210 DCOD(JUL, 2, 1), DCOD(AUG, 2, 1), DCOD(SEP, 2, 1), DCOD(OCT, 2, 1),
211 DCOD(NOV, 2, 1), DCOD(DEC, 2, 1), 0, 0,
212 0, DCOD( 0, 3, 1), DCOD(JAN, 3, 1), DCOD(FEB, 3, 1),
213 DCOD(MAR, 3, 1), DCOD(APR, 3, 1), DCOD(MAY, 3, 1), DCOD(JUN, 3, 1),
214 DCOD(JUL, 3, 1), DCOD(AUG, 3, 1), DCOD(SEP, 3, 1), DCOD(OCT, 3, 1),
215 DCOD(NOV, 3, 1), DCOD(DEC, 3, 1), 0, 0
216 };
217
218 void
fattime2timespec(unsigned dd,unsigned dt,unsigned dh,int utc,struct timespec * tsp)219 fattime2timespec(unsigned dd, unsigned dt, unsigned dh, int utc,
220 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
main(int argc __unused,char ** argv __unused)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