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glibc/time/mktime.c
Roland McGrath 28f540f45b initial import
1995-02-18 01:27:10 +00:00

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/* Copyright (C) 1993, 1994, 1995 Free Software Foundation, Inc.
Contributed by Noel Cragg (noel@cs.oberlin.edu), with fixes by
Michael E. Calwas (calwas@ttd.teradyne.com) and
Wade Hampton (tasi029@tmn.com).
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Library General Public License for more details.
You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB. If
not, write to the Free Software Foundation, Inc., 675 Mass Ave,
Cambridge, MA 02139, USA. */
/* Define this to have a standalone program to test this implementation of
mktime. */
/* #define DEBUG */
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#include <sys/types.h> /* Some systems define `time_t' here. */
#include <time.h>
#ifndef __isleap
/* Nonzero if YEAR is a leap year (every 4 years,
except every 100th isn't, and every 400th is). */
#define __isleap(year) \
((year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0))
#endif
#ifndef __P
#if defined (__GNUC__) || (defined (__STDC__) && __STDC__)
#define __P(args) args
#else
#define __P(args) ()
#endif /* GCC. */
#endif /* Not __P. */
/* How many days are in each month. */
const unsigned short int __mon_lengths[2][12] =
{
/* Normal years. */
{ 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 },
/* Leap years. */
{ 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 }
};
static int times_through_search; /* This library routine should never
hang -- make sure we always return
when we're searching for a value */
#ifdef DEBUG
#include <stdio.h>
#include <ctype.h>
int debugging_enabled = 0;
/* Print the values in a `struct tm'. */
static void
printtm (it)
struct tm *it;
{
printf ("%02d/%02d/%04d %02d:%02d:%02d (%s) yday:%03d dst:%d gmtoffset:%ld",
it->tm_mon + 1,
it->tm_mday,
it->tm_year + 1900,
it->tm_hour,
it->tm_min,
it->tm_sec,
it->tm_zone,
it->tm_yday,
it->tm_isdst,
it->tm_gmtoff);
}
#endif
static time_t
dist_tm (t1, t2)
struct tm *t1;
struct tm *t2;
{
time_t distance = 0;
unsigned long int v1, v2;
int diff_flag = 0;
v1 = v2 = 0;
#define doit(x, secs) \
v1 += t1->x * secs; \
v2 += t2->x * secs; \
if (!diff_flag) \
{ \
if (t1->x < t2->x) \
diff_flag = -1; \
else if (t1->x > t2->x) \
diff_flag = 1; \
}
doit (tm_year, 31536000); /* Okay, not all years have 365 days. */
doit (tm_mon, 2592000); /* Okay, not all months have 30 days. */
doit (tm_mday, 86400);
doit (tm_hour, 3600);
doit (tm_min, 60);
doit (tm_sec, 1);
#undef doit
/* We should also make sure that the sign of DISTANCE is correct -- if
DIFF_FLAG is positive, the distance should be positive and vice versa. */
distance = (v1 > v2) ? (v1 - v2) : (v2 - v1);
if (diff_flag < 0)
distance = -distance;
if (times_through_search > 20) /* Arbitrary # of calls, but makes sure we
never hang if there's a problem with
this algorithm. */
{
distance = diff_flag;
}
/* We need this DIFF_FLAG business because it is forseeable that the
distance may be zero when, in actuality, the two structures are
different. This is usually the case when the dates are 366 days apart
and one of the years is a leap year. */
if (distance == 0 && diff_flag)
distance = 86400 * diff_flag;
return distance;
}
/* MKTIME converts the values in a struct tm to a time_t. The values
in tm_wday and tm_yday are ignored; other values can be put outside
of legal ranges since they will be normalized. This routine takes
care of that normalization. */
void
do_normalization (tmptr)
struct tm *tmptr;
{
#define normalize(foo,x,y,bar); \
while (tmptr->foo < x) \
{ \
tmptr->bar--; \
tmptr->foo = (y - (x - tmptr->foo) + 1); \
} \
while (tmptr->foo > y) \
{ \
tmptr->foo = (x + (tmptr->foo - y) - 1); \
tmptr->bar++; \
}
normalize (tm_sec, 0, 59, tm_min);
normalize (tm_min, 0, 59, tm_hour);
normalize (tm_hour, 0, 23, tm_mday);
/* Do the month first, so day range can be found. */
normalize (tm_mon, 0, 11, tm_year);
/* Since the day range modifies the month, we should be careful how
we reference the array of month lengths -- it is possible that
the month will go negative, hence the modulo...
Also, tm_year is the year - 1900, so we have to 1900 to have it
work correctly. */
normalize (tm_mday, 1,
__mon_lengths[__isleap (tmptr->tm_year + 1900)]
[((tmptr->tm_mon < 0)
? (12 + (tmptr->tm_mon % 12))
: (tmptr->tm_mon % 12)) ],
tm_mon);
/* Do the month again, because the day may have pushed it out of range. */
normalize (tm_mon, 0, 11, tm_year);
/* Do the day again, because the month may have changed the range. */
normalize (tm_mday, 1,
__mon_lengths[__isleap (tmptr->tm_year + 1900)]
[((tmptr->tm_mon < 0)
? (12 + (tmptr->tm_mon % 12))
: (tmptr->tm_mon % 12)) ],
tm_mon);
#ifdef DEBUG
if (debugging_enabled)
{
printf (" After normalizing:\n ");
printtm (tmptr);
putchar ('\n');
}
#endif
}
/* Here's where the work gets done. */
#define BAD_STRUCT_TM ((time_t) -1)
time_t
_mktime_internal (timeptr, producer)
struct tm *timeptr;
struct tm *(*producer) __P ((const time_t *));
{
struct tm our_tm; /* our working space */
struct tm *me = &our_tm; /* a pointer to the above */
time_t result; /* the value we return */
*me = *timeptr; /* copy the struct tm that was passed
in by the caller */
/***************************/
/* Normalize the structure */
/***************************/
/* This routine assumes that the value of TM_ISDST is -1, 0, or 1.
If the user didn't pass it in that way, fix it. */
if (me->tm_isdst > 0)
me->tm_isdst = 1;
else if (me->tm_isdst < 0)
me->tm_isdst = -1;
do_normalization (me);
/* Get out of here if it's not possible to represent this struct.
If any of the values in the normalized struct tm are negative,
our algorithms won't work. Luckily, we only need to check the
year at this point; normalization guarantees that all values will
be in correct ranges EXCEPT the year. */
if (me->tm_year < 0)
return BAD_STRUCT_TM;
/*************************************************/
/* Find the appropriate time_t for the structure */
/*************************************************/
/* Modified b-search -- make intelligent guesses as to where the
time might lie along the timeline, assuming that our target time
lies a linear distance (w/o considering time jumps of a
particular region).
Assume that time does not fluctuate at all along the timeline --
e.g., assume that a day will always take 86400 seconds, etc. --
and come up with a hypothetical value for the time_t
representation of the struct tm TARGET, in relation to the guess
variable -- it should be pretty close!
After testing this, the maximum number of iterations that I had
on any number that I tried was 3! Not bad.
The reason this is not a subroutine is that we will modify some
fields in the struct tm (yday and mday). I've never felt good
about side-effects when writing structured code... */
{
struct tm *guess_tm;
time_t guess = 0;
time_t distance = 0;
time_t last_distance = 0;
times_through_search = 0;
do
{
guess += distance;
times_through_search++;
guess_tm = (*producer) (&guess);
#ifdef DEBUG
if (debugging_enabled)
{
printf (" Guessing time_t == %d\n ", (int) guess);
printtm (guess_tm);
putchar ('\n');
}
#endif
/* How far is our guess from the desired struct tm? */
distance = dist_tm (me, guess_tm);
/* Handle periods of time where a period of time is skipped.
For example, 2:15 3 April 1994 does not exist, because DST
is in effect. The distance function will alternately
return values of 3600 and -3600, because it doesn't know
that the requested time doesn't exist. In these situations
(even if the skip is not exactly an hour) the distances
returned will be the same, but alternating in sign. We
want the later time, so check to see that the distance is
oscillating and we've chosen the correct of the two
possibilities.
Useful: 3 Apr 94 765356300, 30 Oct 94 783496000 */
if ((distance == -last_distance) && (distance < last_distance))
{
/* If the caller specified that the DST flag was off, it's
not possible to represent this time. */
if (me->tm_isdst == 0)
{
#ifdef DEBUG
printf (" Distance is oscillating -- dst flag nixes struct!\n");
#endif
return BAD_STRUCT_TM;
}
#ifdef DEBUG
printf (" Distance is oscillating -- chose the later time.\n");
#endif
distance = 0;
}
if ((distance == 0) && (me->tm_isdst != -1)
&& (me->tm_isdst != guess_tm->tm_isdst))
{
/* If we're in this code, we've got the right time but the
wrong daylight savings flag. We need to move away from
the time that we have and approach the other time from
the other direction. That is, if I've requested the
non-DST version of a time and I get the DST version
instead, I want to put us forward in time and search
backwards to get the other time. I checked all of the
configuration files for the tz package -- no entry
saves more than two hours, so I think we'll be safe by
moving 24 hours in one direction. IF THE AMOUNT OF
TIME SAVED IN THE CONFIGURATION FILES CHANGES, THIS
VALUE MAY NEED TO BE ADJUSTED. Luckily, we can never
have more than one level of overlaps, or this would
never work. */
#define SKIP_VALUE 86400
if (guess_tm->tm_isdst == 0)
/* we got the later one, but want the earlier one */
distance = -SKIP_VALUE;
else
distance = SKIP_VALUE;
#ifdef DEBUG
printf (" Got the right time, wrong DST value -- adjusting\n");
#endif
}
last_distance = distance;
} while (distance != 0);
/* Check to see that the dst flag matches */
if (me->tm_isdst != -1)
{
if (me->tm_isdst != guess_tm->tm_isdst)
{
#ifdef DEBUG
printf (" DST flag doesn't match! FIXME?\n");
#endif
return BAD_STRUCT_TM;
}
}
result = guess; /* Success! */
/* On successful completion, the values of tm_wday and tm_yday
have to be set appropriately. */
/* me->tm_yday = guess_tm->tm_yday;
me->tm_mday = guess_tm->tm_mday; */
*me = *guess_tm;
}
/* Update the caller's version of the structure */
*timeptr = *me;
return result;
}
time_t
#ifdef DEBUG /* make it work even if the system's
libc has it's own mktime routine */
my_mktime (timeptr)
#else
mktime (timeptr)
#endif
struct tm *timeptr;
{
return _mktime_internal (timeptr, localtime);
}
#ifdef weak_alias
weak_alias (mktime, timelocal)
#endif
#ifdef DEBUG
void
main (argc, argv)
int argc;
char *argv[];
{
int time;
int result_time;
struct tm *tmptr;
if (argc == 1)
{
long q;
printf ("starting long test...\n");
for (q = 10000000; q < 1000000000; q += 599)
{
struct tm *tm = localtime ((time_t *) &q);
if ((q % 10000) == 0) { printf ("%ld\n", q); fflush (stdout); }
if (q != my_mktime (tm))
{ printf ("failed for %ld\n", q); fflush (stdout); }
}
printf ("test finished\n");
exit (0);
}
if (argc != 2)
{
printf ("wrong # of args\n");
exit (0);
}
debugging_enabled = 1; /* We want to see the info */
++argv;
time = atoi (*argv);
tmptr = localtime ((time_t *) &time);
printf ("Localtime tells us that a time_t of %d represents\n ", time);
printtm (tmptr);
putchar ('\n');
printf (" Given localtime's return val, mktime returns %d which is\n ",
(int) my_mktime (tmptr));
printtm (tmptr);
putchar ('\n');
#if 0
tmptr->tm_sec -= 20;
tmptr->tm_min -= 20;
tmptr->tm_hour -= 20;
tmptr->tm_mday -= 20;
tmptr->tm_mon -= 20;
tmptr->tm_year -= 20;
tmptr->tm_gmtoff -= 20000; /* This has no effect! */
tmptr->tm_zone = NULL; /* Nor does this! */
tmptr->tm_isdst = -1;
#endif
tmptr->tm_hour += 1;
tmptr->tm_isdst = -1;
printf ("\n\nchanged ranges: ");
printtm (tmptr);
putchar ('\n');
result_time = my_mktime (tmptr);
printf ("\nmktime: %d\n", result_time);
tmptr->tm_isdst = 0;
printf ("\n\nchanged ranges: ");
printtm (tmptr);
putchar ('\n');
result_time = my_mktime (tmptr);
printf ("\nmktime: %d\n", result_time);
}
#endif /* DEBUG */
/*
Local Variables:
compile-command: "gcc -g mktime.c -o mktime -DDEBUG"
End:
*/
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