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freebsd/sys/kern/subr_fattime.c

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/*-
* Copyright (c) 2006 Poul-Henning Kamp
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* $FreeBSD$
*
* Convert MS-DOS FAT format timestamps to and from unix timespecs
*
* FAT filestamps originally consisted of two 16 bit integers, encoded like
* this:
*
* yyyyyyymmmmddddd (year - 1980, month, day)
*
* hhhhhmmmmmmsssss (hour, minutes, seconds divided by two)
*
* Subsequently even Microsoft realized that files could be accessed in less
* than two seconds and a byte was added containing:
*
* sfffffff (second mod two, 100ths of second)
*
* FAT timestamps are in the local timezone, with no indication of which
* timezone much less if daylight savings time applies.
*
* Later on again, in Windows NT, timestamps were defined relative to GMT.
*
* Purists will point out that UTC replaced GMT for such uses around
* a century ago, already then. Ironically "NT" was an abbreviation of
* "New Technology". Anyway...
*
* The 'utc' argument determines if the resulting FATTIME timestamp
* should be on the UTC or local timezone calendar.
*
* The conversion functions below cut time into four-year leap-year
* cycles rather than single years and uses table lookups inside those
* cycles to get the months and years sorted out.
*
* Obviously we cannot calculate the correct table index going from
* a posix seconds count to Y/M/D, but we can get pretty close by
* dividing the daycount by 32 (giving a too low index), and then
* adjusting upwards a couple of steps if necessary.
*
* FAT timestamps have 7 bits for the year and starts at 1980, so
* they can represent up to 2107 which means that the non-leap-year
* 2100 must be handled.
*
* XXX: As long as time_t is 32 bits this is not relevant or easily
* XXX: testable. Revisit when time_t grows bigger.
* XXX: grepfodder: 64 bit time_t, y2100, y2.1k, 2100, leap year
*
*/
#include <sys/param.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/clock.h>
#define DAY (24 * 60 * 60) /* Length of day in seconds */
#define YEAR 365 /* Length of normal year */
#define LYC (4 * YEAR + 1) /* Length of 4 year leap-year cycle */
#define T1980 (10 * 365 + 2) /* Days from 1970 to 1980 */
/* End of month is N days from start of (normal) year */
#define JAN 31
#define FEB (JAN + 28)
#define MAR (FEB + 31)
#define APR (MAR + 30)
#define MAY (APR + 31)
#define JUN (MAY + 30)
#define JUL (JUN + 31)
#define AUG (JUL + 31)
#define SEP (AUG + 30)
#define OCT (SEP + 31)
#define NOV (OCT + 30)
#define DEC (NOV + 31)
/* Table of months in a 4 year leap-year cycle */
#define ENC(y,m) (((y) << 9) | ((m) << 5))
static const struct {
uint16_t days; /* month start in days relative to cycle */
uint16_t coded; /* encoded year + month information */
} mtab[48] = {
{ 0 + 0 * YEAR, ENC(0, 1) },
{ JAN + 0 * YEAR, ENC(0, 2) }, { FEB + 0 * YEAR + 1, ENC(0, 3) },
{ MAR + 0 * YEAR + 1, ENC(0, 4) }, { APR + 0 * YEAR + 1, ENC(0, 5) },
{ MAY + 0 * YEAR + 1, ENC(0, 6) }, { JUN + 0 * YEAR + 1, ENC(0, 7) },
{ JUL + 0 * YEAR + 1, ENC(0, 8) }, { AUG + 0 * YEAR + 1, ENC(0, 9) },
{ SEP + 0 * YEAR + 1, ENC(0, 10) }, { OCT + 0 * YEAR + 1, ENC(0, 11) },
{ NOV + 0 * YEAR + 1, ENC(0, 12) }, { DEC + 0 * YEAR + 1, ENC(1, 1) },
{ JAN + 1 * YEAR + 1, ENC(1, 2) }, { FEB + 1 * YEAR + 1, ENC(1, 3) },
{ MAR + 1 * YEAR + 1, ENC(1, 4) }, { APR + 1 * YEAR + 1, ENC(1, 5) },
{ MAY + 1 * YEAR + 1, ENC(1, 6) }, { JUN + 1 * YEAR + 1, ENC(1, 7) },
{ JUL + 1 * YEAR + 1, ENC(1, 8) }, { AUG + 1 * YEAR + 1, ENC(1, 9) },
{ SEP + 1 * YEAR + 1, ENC(1, 10) }, { OCT + 1 * YEAR + 1, ENC(1, 11) },
{ NOV + 1 * YEAR + 1, ENC(1, 12) }, { DEC + 1 * YEAR + 1, ENC(2, 1) },
{ JAN + 2 * YEAR + 1, ENC(2, 2) }, { FEB + 2 * YEAR + 1, ENC(2, 3) },
{ MAR + 2 * YEAR + 1, ENC(2, 4) }, { APR + 2 * YEAR + 1, ENC(2, 5) },
{ MAY + 2 * YEAR + 1, ENC(2, 6) }, { JUN + 2 * YEAR + 1, ENC(2, 7) },
{ JUL + 2 * YEAR + 1, ENC(2, 8) }, { AUG + 2 * YEAR + 1, ENC(2, 9) },
{ SEP + 2 * YEAR + 1, ENC(2, 10) }, { OCT + 2 * YEAR + 1, ENC(2, 11) },
{ NOV + 2 * YEAR + 1, ENC(2, 12) }, { DEC + 2 * YEAR + 1, ENC(3, 1) },
{ JAN + 3 * YEAR + 1, ENC(3, 2) }, { FEB + 3 * YEAR + 1, ENC(3, 3) },
{ MAR + 3 * YEAR + 1, ENC(3, 4) }, { APR + 3 * YEAR + 1, ENC(3, 5) },
{ MAY + 3 * YEAR + 1, ENC(3, 6) }, { JUN + 3 * YEAR + 1, ENC(3, 7) },
{ JUL + 3 * YEAR + 1, ENC(3, 8) }, { AUG + 3 * YEAR + 1, ENC(3, 9) },
{ SEP + 3 * YEAR + 1, ENC(3, 10) }, { OCT + 3 * YEAR + 1, ENC(3, 11) },
{ NOV + 3 * YEAR + 1, ENC(3, 12) }
};
void
timespec2fattime(struct timespec *tsp, int utc, uint16_t *ddp, uint16_t *dtp, uint8_t *dhp)
{
time_t t1;
unsigned t2, l, m;
t1 = tsp->tv_sec;
if (!utc)
t1 -= utc_offset();
if (dhp != NULL)
*dhp = (tsp->tv_sec & 1) * 100 + tsp->tv_nsec / 10000000;
if (dtp != NULL) {
*dtp = (t1 / 2) % 30;
*dtp |= ((t1 / 60) % 60) << 5;
*dtp |= ((t1 / 3600) % 24) << 11;
}
if (ddp != NULL) {
t2 = t1 / DAY;
if (t2 < T1980) {
/* Impossible date, truncate to 1980-01-01 */
*ddp = 0x0021;
} else {
t2 -= T1980;
/*
* 2100 is not a leap year.
* XXX: a 32 bit time_t can not get us here.
*/
if (t2 >= ((2100 - 1980) / 4 * LYC + FEB))
t2++;
/* Account for full leapyear cycles */
l = t2 / LYC;
*ddp = (l * 4) << 9;
t2 -= l * LYC;
/* Find approximate table entry */
m = t2 / 32;
/* Find correct table entry */
while (m < 47 && mtab[m + 1].days <= t2)
m++;
/* Get year + month from the table */
*ddp += mtab[m].coded;
/* And apply the day in the month */
t2 -= mtab[m].days - 1;
*ddp |= t2;
}
}
}
/*
* Table indexed by the bottom two bits of year + four bits of the month
* from the FAT timestamp, returning number of days into 4 year long
* leap-year cycle
*/
#define DCOD(m, y, l) ((m) + YEAR * (y) + (l))
static const uint16_t daytab[64] = {
0, DCOD( 0, 0, 0), DCOD(JAN, 0, 0), DCOD(FEB, 0, 1),
DCOD(MAR, 0, 1), DCOD(APR, 0, 1), DCOD(MAY, 0, 1), DCOD(JUN, 0, 1),
DCOD(JUL, 0, 1), DCOD(AUG, 0, 1), DCOD(SEP, 0, 1), DCOD(OCT, 0, 1),
DCOD(NOV, 0, 1), DCOD(DEC, 0, 1), 0, 0,
0, DCOD( 0, 1, 1), DCOD(JAN, 1, 1), DCOD(FEB, 1, 1),
DCOD(MAR, 1, 1), DCOD(APR, 1, 1), DCOD(MAY, 1, 1), DCOD(JUN, 1, 1),
DCOD(JUL, 1, 1), DCOD(AUG, 1, 1), DCOD(SEP, 1, 1), DCOD(OCT, 1, 1),
DCOD(NOV, 1, 1), DCOD(DEC, 1, 1), 0, 0,
0, DCOD( 0, 2, 1), DCOD(JAN, 2, 1), DCOD(FEB, 2, 1),
DCOD(MAR, 2, 1), DCOD(APR, 2, 1), DCOD(MAY, 2, 1), DCOD(JUN, 2, 1),
DCOD(JUL, 2, 1), DCOD(AUG, 2, 1), DCOD(SEP, 2, 1), DCOD(OCT, 2, 1),
DCOD(NOV, 2, 1), DCOD(DEC, 2, 1), 0, 0,
0, DCOD( 0, 3, 1), DCOD(JAN, 3, 1), DCOD(FEB, 3, 1),
DCOD(MAR, 3, 1), DCOD(APR, 3, 1), DCOD(MAY, 3, 1), DCOD(JUN, 3, 1),
DCOD(JUL, 3, 1), DCOD(AUG, 3, 1), DCOD(SEP, 3, 1), DCOD(OCT, 3, 1),
DCOD(NOV, 3, 1), DCOD(DEC, 3, 1), 0, 0
};
void
fattime2timespec(unsigned dd, unsigned dt, unsigned dh, int utc, struct timespec *tsp)
{
unsigned day;
/* Unpack time fields */
tsp->tv_sec = (dt & 0x1f) << 1;
tsp->tv_sec += ((dt & 0x7e0) >> 5) * 60;
tsp->tv_sec += ((dt & 0xf800) >> 11) * 3600;
tsp->tv_sec += dh / 100;
tsp->tv_nsec = (dh % 100) * 10000000;
/* Day of month */
day = (dd & 0x1f) - 1;
/* Full leap-year cycles */
day += LYC * ((dd >> 11) & 0x1f);
/* Month offset from leap-year cycle */
day += daytab[(dd >> 5) & 0x3f];
/*
* 2100 is not a leap year.
* XXX: a 32 bit time_t can not get us here.
*/
if (day >= ((2100 - 1980) / 4 * LYC + FEB))
day--;
/* Align with time_t epoch */
day += T1980;
tsp->tv_sec += DAY * day;
if (!utc)
tsp->tv_sec += utc_offset();
}
#ifdef TEST_DRIVER
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
int
main(int argc __unused, char **argv __unused)
{
int i;
struct timespec ts;
struct tm tm;
double a;
uint16_t d, t;
uint8_t p;
char buf[100];
for (i = 0; i < 10000; i++) {
do {
ts.tv_sec = random();
} while (ts.tv_sec < T1980 * 86400);
ts.tv_nsec = random() % 1000000000;
printf("%10d.%03ld -- ", ts.tv_sec, ts.tv_nsec / 1000000);
gmtime_r(&ts.tv_sec, &tm);
strftime(buf, sizeof buf, "%Y %m %d %H %M %S", &tm);
printf("%s -- ", buf);
a = ts.tv_sec + ts.tv_nsec * 1e-9;
d = t = p = 0;
timet2fattime(&ts, &d, &t, &p);
printf("%04x %04x %02x -- ", d, t, p);
printf("%3d %02d %02d %02d %02d %02d -- ",
((d >> 9) & 0x7f) + 1980,
(d >> 5) & 0x0f,
(d >> 0) & 0x1f,
(t >> 11) & 0x1f,
(t >> 5) & 0x3f,
((t >> 0) & 0x1f) * 2);
ts.tv_sec = ts.tv_nsec = 0;
fattime2timet(d, t, p, &ts);
printf("%10d.%03ld == ", ts.tv_sec, ts.tv_nsec / 1000000);
gmtime_r(&ts.tv_sec, &tm);
strftime(buf, sizeof buf, "%Y %m %d %H %M %S", &tm);
printf("%s -- ", buf);
a -= ts.tv_sec + ts.tv_nsec * 1e-9;
printf("%.3f", a);
printf("\n");
}
return (0);
}
#endif /* TEST_DRIVER */
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