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 * 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 void 137 timespec2fattime(const struct timespec *tsp, int utc, uint16_t *ddp, 138 uint16_t *dtp, uint8_t *dhp) 139 { 140 time_t t1; 141 unsigned t2, l, m; 142 143 t1 = tsp->tv_sec; 144 if (!utc) 145 t1 -= utc_offset(); 146 147 if (dhp != NULL) 148 *dhp = (tsp->tv_sec & 1) * 100 + tsp->tv_nsec / 10000000; 149 if (dtp != NULL) { 150 *dtp = (t1 / 2) % 30; 151 *dtp |= ((t1 / 60) % 60) << 5; 152 *dtp |= ((t1 / 3600) % 24) << 11; 153 } 154 if (ddp != NULL) { 155 t2 = t1 / DAY; 156 if (t2 < T1980) { 157 /* Impossible date, truncate to 1980-01-01 */ 158 *ddp = 0x0021; 159 } else { 160 t2 -= T1980; 161 162 /* 163 * 2100 is not a leap year. 164 * XXX: a 32 bit time_t can not get us here. 165 */ 166 if (t2 >= ((2100 - 1980) / 4 * LYC + FEB)) 167 t2++; 168 169 /* Account for full leapyear cycles */ 170 l = t2 / LYC; 171 *ddp = (l * 4) << 9; 172 t2 -= l * LYC; 173 174 /* Find approximate table entry */ 175 m = t2 / 32; 176 177 /* Find correct table entry */ 178 while (m < 47 && mtab[m + 1].days <= t2) 179 m++; 180 181 /* Get year + month from the table */ 182 *ddp += mtab[m].coded; 183 184 /* And apply the day in the month */ 185 t2 -= mtab[m].days - 1; 186 *ddp |= t2; 187 } 188 } 189 } 190 191 /* 192 * Table indexed by the bottom two bits of year + four bits of the month 193 * from the FAT timestamp, returning number of days into 4 year long 194 * leap-year cycle 195 */ 196 197 #define DCOD(m, y, l) ((m) + YEAR * (y) + (l)) 198 static const uint16_t daytab[64] = { 199 0, DCOD( 0, 0, 0), DCOD(JAN, 0, 0), DCOD(FEB, 0, 1), 200 DCOD(MAR, 0, 1), DCOD(APR, 0, 1), DCOD(MAY, 0, 1), DCOD(JUN, 0, 1), 201 DCOD(JUL, 0, 1), DCOD(AUG, 0, 1), DCOD(SEP, 0, 1), DCOD(OCT, 0, 1), 202 DCOD(NOV, 0, 1), DCOD(DEC, 0, 1), 0, 0, 203 0, DCOD( 0, 1, 1), DCOD(JAN, 1, 1), DCOD(FEB, 1, 1), 204 DCOD(MAR, 1, 1), DCOD(APR, 1, 1), DCOD(MAY, 1, 1), DCOD(JUN, 1, 1), 205 DCOD(JUL, 1, 1), DCOD(AUG, 1, 1), DCOD(SEP, 1, 1), DCOD(OCT, 1, 1), 206 DCOD(NOV, 1, 1), DCOD(DEC, 1, 1), 0, 0, 207 0, DCOD( 0, 2, 1), DCOD(JAN, 2, 1), DCOD(FEB, 2, 1), 208 DCOD(MAR, 2, 1), DCOD(APR, 2, 1), DCOD(MAY, 2, 1), DCOD(JUN, 2, 1), 209 DCOD(JUL, 2, 1), DCOD(AUG, 2, 1), DCOD(SEP, 2, 1), DCOD(OCT, 2, 1), 210 DCOD(NOV, 2, 1), DCOD(DEC, 2, 1), 0, 0, 211 0, DCOD( 0, 3, 1), DCOD(JAN, 3, 1), DCOD(FEB, 3, 1), 212 DCOD(MAR, 3, 1), DCOD(APR, 3, 1), DCOD(MAY, 3, 1), DCOD(JUN, 3, 1), 213 DCOD(JUL, 3, 1), DCOD(AUG, 3, 1), DCOD(SEP, 3, 1), DCOD(OCT, 3, 1), 214 DCOD(NOV, 3, 1), DCOD(DEC, 3, 1), 0, 0 215 }; 216 217 void 218 fattime2timespec(unsigned dd, unsigned dt, unsigned dh, int utc, 219 struct timespec *tsp) 220 { 221 unsigned day; 222 223 /* Unpack time fields */ 224 tsp->tv_sec = (dt & 0x1f) << 1; 225 tsp->tv_sec += ((dt & 0x7e0) >> 5) * 60; 226 tsp->tv_sec += ((dt & 0xf800) >> 11) * 3600; 227 tsp->tv_sec += dh / 100; 228 tsp->tv_nsec = (dh % 100) * 10000000; 229 230 /* Day of month */ 231 day = (dd & 0x1f) - 1; 232 233 /* Full leap-year cycles */ 234 day += LYC * ((dd >> 11) & 0x1f); 235 236 /* Month offset from leap-year cycle */ 237 day += daytab[(dd >> 5) & 0x3f]; 238 239 /* 240 * 2100 is not a leap year. 241 * XXX: a 32 bit time_t can not get us here. 242 */ 243 if (day >= ((2100 - 1980) / 4 * LYC + FEB)) 244 day--; 245 246 /* Align with time_t epoch */ 247 day += T1980; 248 249 tsp->tv_sec += DAY * day; 250 if (!utc) 251 tsp->tv_sec += utc_offset(); 252 } 253 254 #ifdef TEST_DRIVER 255 256 #include <stdio.h> 257 #include <unistd.h> 258 #include <stdlib.h> 259 260 int 261 main(int argc __unused, char **argv __unused) 262 { 263 int i; 264 struct timespec ts; 265 struct tm tm; 266 double a; 267 uint16_t d, t; 268 uint8_t p; 269 char buf[100]; 270 271 for (i = 0; i < 10000; i++) { 272 do { 273 ts.tv_sec = random(); 274 } while (ts.tv_sec < T1980 * 86400); 275 ts.tv_nsec = random() % 1000000000; 276 277 printf("%10d.%03ld -- ", ts.tv_sec, ts.tv_nsec / 1000000); 278 279 gmtime_r(&ts.tv_sec, &tm); 280 strftime(buf, sizeof buf, "%Y %m %d %H %M %S", &tm); 281 printf("%s -- ", buf); 282 283 a = ts.tv_sec + ts.tv_nsec * 1e-9; 284 d = t = p = 0; 285 timet2fattime(&ts, &d, &t, &p); 286 printf("%04x %04x %02x -- ", d, t, p); 287 printf("%3d %02d %02d %02d %02d %02d -- ", 288 ((d >> 9) & 0x7f) + 1980, 289 (d >> 5) & 0x0f, 290 (d >> 0) & 0x1f, 291 (t >> 11) & 0x1f, 292 (t >> 5) & 0x3f, 293 ((t >> 0) & 0x1f) * 2); 294 295 ts.tv_sec = ts.tv_nsec = 0; 296 fattime2timet(d, t, p, &ts); 297 printf("%10d.%03ld == ", ts.tv_sec, ts.tv_nsec / 1000000); 298 gmtime_r(&ts.tv_sec, &tm); 299 strftime(buf, sizeof buf, "%Y %m %d %H %M %S", &tm); 300 printf("%s -- ", buf); 301 a -= ts.tv_sec + ts.tv_nsec * 1e-9; 302 printf("%.3f", a); 303 printf("\n"); 304 } 305 return (0); 306 } 307 308 #endif /* TEST_DRIVER */ 309