The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/kern/subr_fattime.c

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    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: releng/11.0/sys/kern/subr_fattime.c 275985 2014-12-21 05:07:11Z imp $
   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
  138 timespec2fattime(struct timespec *tsp, int utc, uint16_t *ddp, 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, struct timespec *tsp)
  219 {
  220         unsigned day;
  221 
  222         /* Unpack time fields */
  223         tsp->tv_sec = (dt & 0x1f) << 1;
  224         tsp->tv_sec += ((dt & 0x7e0) >> 5) * 60;
  225         tsp->tv_sec += ((dt & 0xf800) >> 11) * 3600;
  226         tsp->tv_sec += dh / 100;
  227         tsp->tv_nsec = (dh % 100) * 10000000;
  228 
  229         /* Day of month */
  230         day = (dd & 0x1f) - 1;
  231 
  232         /* Full leap-year cycles */
  233         day += LYC * ((dd >> 11) & 0x1f);
  234 
  235         /* Month offset from leap-year cycle */
  236         day += daytab[(dd >> 5) & 0x3f];
  237 
  238         /*
  239          * 2100 is not a leap year.
  240          * XXX: a 32 bit time_t can not get us here.
  241          */
  242         if (day >= ((2100 - 1980) / 4 * LYC + FEB))
  243                 day--;
  244 
  245         /* Align with time_t epoch */
  246         day += T1980;
  247 
  248         tsp->tv_sec += DAY * day;
  249         if (!utc)
  250                 tsp->tv_sec += utc_offset();
  251 }
  252 
  253 #ifdef TEST_DRIVER
  254 
  255 #include <stdio.h>
  256 #include <unistd.h>
  257 #include <stdlib.h>
  258 
  259 int
  260 main(int argc __unused, char **argv __unused)
  261 {
  262         int i;
  263         struct timespec ts;
  264         struct tm tm;
  265         double a;
  266         uint16_t d, t;
  267         uint8_t p;
  268         char buf[100];
  269 
  270         for (i = 0; i < 10000; i++) {
  271                 do {
  272                         ts.tv_sec = random();
  273                 } while (ts.tv_sec < T1980 * 86400);
  274                 ts.tv_nsec = random() % 1000000000;
  275 
  276                 printf("%10d.%03ld -- ", ts.tv_sec, ts.tv_nsec / 1000000);
  277 
  278                 gmtime_r(&ts.tv_sec, &tm);
  279                 strftime(buf, sizeof buf, "%Y %m %d %H %M %S", &tm);
  280                 printf("%s -- ", buf);
  281 
  282                 a = ts.tv_sec + ts.tv_nsec * 1e-9;
  283                 d = t = p = 0;
  284                 timet2fattime(&ts, &d, &t, &p);
  285                 printf("%04x %04x %02x -- ", d, t, p);
  286                 printf("%3d %02d %02d %02d %02d %02d -- ",
  287                     ((d >> 9)  & 0x7f) + 1980,
  288                     (d >> 5)  & 0x0f,
  289                     (d >> 0)  & 0x1f,
  290                     (t >> 11) & 0x1f,
  291                     (t >> 5)  & 0x3f,
  292                     ((t >> 0)  & 0x1f) * 2);
  293 
  294                 ts.tv_sec = ts.tv_nsec = 0;
  295                 fattime2timet(d, t, p, &ts);
  296                 printf("%10d.%03ld == ", ts.tv_sec, ts.tv_nsec / 1000000);
  297                 gmtime_r(&ts.tv_sec, &tm);
  298                 strftime(buf, sizeof buf, "%Y %m %d %H %M %S", &tm);
  299                 printf("%s -- ", buf);
  300                 a -= ts.tv_sec + ts.tv_nsec * 1e-9;
  301                 printf("%.3f", a);
  302                 printf("\n");
  303         }
  304         return (0);
  305 }
  306 
  307 #endif /* TEST_DRIVER */

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