subr_fattime.c revision 163611
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: head/sys/kern/subr_fattime.c 163611 2006-10-22 18:19:08Z phk $ 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 * a century ago, already then. Ironically "NT" was an abbreviation of 49 * "New Technology". Anyway... 50 * 51 * The functions below always assume UTC time, and the calling code 52 * must apply the local timezone offset as appropriate. Unless special 53 * conditions apply, the utc_offset() function be used for this. 54 * 55 * The conversion functions below cut time into four-year leap-second 56 * cycles rather than single years and uses table lookups inside those 57 * cycles to get the months and years sorted out. 58 * 59 * Obviously we cannot calculate the correct table index going from 60 * a posix seconds count to Y/M/D, but we can get pretty close by 61 * dividing the daycount by 32 (giving a too low index), and then 62 * adjusting upwards a couple of steps if necessary. 63 * 64 * FAT timestamps have 7 bits for the year and starts at 1980, so 65 * they can represent up to 2107 which means that the non-leap-year 66 * 2100 must be handled. 67 * 68 * XXX: As long as time_t is 32 bits this is not relevant or easily 69 * XXX: testable. Revisit when time_t grows bigger. 70 * XXX: grepfodder: 64 bit time_t, y2100, y2.1k, 2100, leap year 71 * 72 */ 73 74#include <sys/param.h> 75#include <sys/types.h> 76#include <sys/time.h> 77#include <sys/clock.h> 78 79#define DAY (24 * 60 * 60) /* Length of day in seconds */ 80#define YEAR 365 /* Length of normal year */ 81#define LYC (4 * YEAR + 1) /* Length of 4 year leap-year cycle */ 82#define T1980 (10 * 365 + 2) /* Days from 1970 to 1980 */ 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 102static 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 138void 139timet2fattime(struct timespec *tsp, u_int16_t *ddp, u_int16_t *dtp, u_int8_t *dhp) 140{ 141 time_t t1; 142 unsigned t2, l, m; 143 144 t1 = tsp->tv_sec; 145 146 if (dhp != NULL) 147 *dhp = (tsp->tv_sec & 1) * 100 + tsp->tv_nsec / 10000000; 148 if (dtp != NULL) { 149 *dtp = (t1 / 2) % 30; 150 *dtp |= ((t1 / 60) % 60) << 5; 151 *dtp |= ((t1 / 3600) % 24) << 11; 152 } 153 if (ddp != NULL) { 154 t2 = t1 / DAY; 155 if (t2 < T1980) { 156 /* Impossible date, truncate to 1980-01-01 */ 157 *ddp = 0x0021; 158 } else { 159 t2 -= T1980; 160 161 /* 162 * 2100 is not a leap year. 163 * XXX: a 32 bit time_t can not get us here. 164 */ 165 if (t2 >= ((2100 - 1980) / 4 * LYC + FEB)) 166 t2++; 167 168 /* Account for full leapyear cycles */ 169 l = t2 / LYC; 170 *ddp = (l * 4) << 9; 171 t2 -= l * LYC; 172 173 /* Find approximate table entry */ 174 m = t2 / 32; 175 176 /* Find correct table entry */ 177 while (m < 47 && mtab[m + 1].days <= t2) 178 m++; 179 180 /* Get year + month from the table */ 181 *ddp += mtab[m].coded; 182 183 /* And apply the day in the month */ 184 t2 -= mtab[m].days - 1; 185 *ddp |= t2; 186 } 187 } 188} 189 190/* 191 * Table indexed by the bottom two bits of year + four bits of the month 192 * from the FAT timestamp, returning number of days into 4 year long 193 * leap-year cycle 194 */ 195 196#define DCOD(m, y, l) ((m) + YEAR * (y) + (l)) 197static const uint16_t daytab[64] = { 198 0, DCOD( 0, 0, 0), DCOD(JAN, 0, 0), DCOD(FEB, 0, 1), 199 DCOD(MAR, 0, 1), DCOD(APR, 0, 1), DCOD(MAY, 0, 1), DCOD(JUN, 0, 1), 200 DCOD(JUL, 0, 1), DCOD(AUG, 0, 1), DCOD(SEP, 0, 1), DCOD(OCT, 0, 1), 201 DCOD(NOV, 0, 1), DCOD(DEC, 0, 1), 0, 0, 202 0, DCOD( 0, 1, 1), DCOD(JAN, 1, 1), DCOD(FEB, 1, 1), 203 DCOD(MAR, 1, 1), DCOD(APR, 1, 1), DCOD(MAY, 1, 1), DCOD(JUN, 1, 1), 204 DCOD(JUL, 1, 1), DCOD(AUG, 1, 1), DCOD(SEP, 1, 1), DCOD(OCT, 1, 1), 205 DCOD(NOV, 1, 1), DCOD(DEC, 1, 1), 0, 0, 206 0, DCOD( 0, 2, 1), DCOD(JAN, 2, 1), DCOD(FEB, 2, 1), 207 DCOD(MAR, 2, 1), DCOD(APR, 2, 1), DCOD(MAY, 2, 1), DCOD(JUN, 2, 1), 208 DCOD(JUL, 2, 1), DCOD(AUG, 2, 1), DCOD(SEP, 2, 1), DCOD(OCT, 2, 1), 209 DCOD(NOV, 2, 1), DCOD(DEC, 2, 1), 0, 0, 210 0, DCOD( 0, 3, 1), DCOD(JAN, 3, 1), DCOD(FEB, 3, 1), 211 DCOD(MAR, 3, 1), DCOD(APR, 3, 1), DCOD(MAY, 3, 1), DCOD(JUN, 3, 1), 212 DCOD(JUL, 3, 1), DCOD(AUG, 3, 1), DCOD(SEP, 3, 1), DCOD(OCT, 3, 1), 213 DCOD(NOV, 3, 1), DCOD(DEC, 3, 1), 0, 0 214}; 215 216void 217fattime2timet(unsigned dd, unsigned dt, unsigned dh, 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 /* 238 * 2100 is not a leap year. 239 * XXX: a 32 bit time_t can not get us here. 240 */ 241 if (day >= ((2100 - 1980) / 4 * LYC + FEB)) 242 day--; 243 244 /* Align with time_t epoch */ 245 day += T1980; 246 247 tsp->tv_sec += DAY * day; 248} 249 250#ifdef TEST_DRIVER 251 252#include <stdio.h> 253#include <unistd.h> 254#include <stdlib.h> 255 256int 257main(int argc __unused, char **argv __unused) 258{ 259 int i; 260 struct timespec ts; 261 struct tm tm; 262 double a; 263 u_int16_t d, t; 264 u_int8_t p; 265 char buf[100]; 266 267 for (i = 0; i < 10000; i++) { 268 do { 269 ts.tv_sec = random(); 270 } while (ts.tv_sec < T1980 * 86400); 271 ts.tv_nsec = random() % 1000000000; 272 273 printf("%10d.%03ld -- ", ts.tv_sec, ts.tv_nsec / 1000000); 274 275 gmtime_r(&ts.tv_sec, &tm); 276 strftime(buf, sizeof buf, "%Y %m %d %H %M %S", &tm); 277 printf("%s -- ", buf); 278 279 a = ts.tv_sec + ts.tv_nsec * 1e-9; 280 d = t = p = 0; 281 timet2fattime(&ts, &d, &t, &p); 282 printf("%04x %04x %02x -- ", d, t, p); 283 printf("%3d %02d %02d %02d %02d %02d -- ", 284 ((d >> 9) & 0x7f) + 1980, 285 (d >> 5) & 0x0f, 286 (d >> 0) & 0x1f, 287 (t >> 11) & 0x1f, 288 (t >> 5) & 0x3f, 289 ((t >> 0) & 0x1f) * 2); 290 291 ts.tv_sec = ts.tv_nsec = 0; 292 fattime2timet(d, t, p, &ts); 293 printf("%10d.%03ld == ", ts.tv_sec, ts.tv_nsec / 1000000); 294 gmtime_r(&ts.tv_sec, &tm); 295 strftime(buf, sizeof buf, "%Y %m %d %H %M %S", &tm); 296 printf("%s -- ", buf); 297 a -= ts.tv_sec + ts.tv_nsec * 1e-9; 298 printf("%.3f", a); 299 printf("\n"); 300 } 301 return (0); 302} 303 304#endif /* TEST_DRIVER */ 305