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a28a0500c0
* time/mktime.c (verify): New macro. (time_t_is_integer, twos_complement_arithmetic, right_shift_propagates_sign, base_year_is_a_multiple_of_100, C99_integer_division): Document these longstanding assumptions in the code, and verify them at compile-time.
534 lines
16 KiB
C
534 lines
16 KiB
C
/* Convert a `struct tm' to a time_t value.
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Copyright (C) 1993-1999, 2002, 2003 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Paul Eggert (eggert@twinsun.com).
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, write to the Free
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Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
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02111-1307 USA. */
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/* Define this to have a standalone program to test this implementation of
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mktime. */
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/* #define DEBUG 1 */
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#ifdef HAVE_CONFIG_H
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# include <config.h>
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#endif
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/* Assume that leap seconds are possible, unless told otherwise.
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If the host has a `zic' command with a `-L leapsecondfilename' option,
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then it supports leap seconds; otherwise it probably doesn't. */
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#ifndef LEAP_SECONDS_POSSIBLE
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# define LEAP_SECONDS_POSSIBLE 1
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#endif
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#include <sys/types.h> /* Some systems define `time_t' here. */
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#include <time.h>
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#include <limits.h>
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#if DEBUG
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# include <stdio.h>
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# include <stdlib.h>
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# include <string.h>
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/* Make it work even if the system's libc has its own mktime routine. */
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# define mktime my_mktime
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#endif /* DEBUG */
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/* The extra casts work around common compiler bugs. */
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#define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
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/* The outer cast is needed to work around a bug in Cray C 5.0.3.0.
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It is necessary at least when t == time_t. */
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#define TYPE_MINIMUM(t) ((t) (TYPE_SIGNED (t) \
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? ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1) : (t) 0))
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#define TYPE_MAXIMUM(t) ((t) (~ (t) 0 - TYPE_MINIMUM (t)))
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#ifndef TIME_T_MIN
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# define TIME_T_MIN TYPE_MINIMUM (time_t)
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#endif
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#ifndef TIME_T_MAX
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# define TIME_T_MAX TYPE_MAXIMUM (time_t)
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#endif
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/* Verify a requirement at compile-time (unlike assert, which is runtime). */
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#define verify(name, assertion) struct name { char a[(assertion) ? 1 : -1]; }
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verify (time_t_is_integer, (time_t) 0.5 == 0);
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verify (twos_complement_arithmetic, -1 == ~1 + 1);
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verify (right_shift_propagates_sign, -1 >> 1 == -1);
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/* The code also assumes that signed integer overflow silently wraps
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around, but this assumption can't be stated without causing a
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diagnostic on some hosts. */
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#define EPOCH_YEAR 1970
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#define TM_YEAR_BASE 1900
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verify (base_year_is_a_multiple_of_100, TM_YEAR_BASE % 100 == 0);
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#ifndef __isleap
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/* Nonzero if YEAR is a leap year (every 4 years,
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except every 100th isn't, and every 400th is). */
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# define __isleap(year) \
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((year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0))
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#endif
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/* How many days come before each month (0-12). */
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#ifndef _LIBC
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static
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#endif
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const unsigned short int __mon_yday[2][13] =
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{
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/* Normal years. */
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{ 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 },
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/* Leap years. */
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{ 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 }
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};
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#ifndef _LIBC
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/* Portable standalone applications should supply a "time_r.h" that
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declares a POSIX-compliant localtime_r, for the benefit of older
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implementations that lack localtime_r or have a nonstandard one.
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See the gnulib time_r module for one way to implement this. */
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# include "time_r.h"
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# undef __localtime_r
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# define __localtime_r localtime_r
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#endif
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/* Yield the difference between (YEAR-YDAY HOUR:MIN:SEC) and (*TP),
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measured in seconds, ignoring leap seconds.
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YEAR uses the same numbering as TM->tm_year.
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All values are in range, except possibly YEAR.
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If TP is null, return a nonzero value.
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If overflow occurs, yield the low order bits of the correct answer. */
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static time_t
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ydhms_tm_diff (int year, int yday, int hour, int min, int sec,
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const struct tm *tp)
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{
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if (!tp)
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return 1;
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else
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{
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verify (C99_integer_division, -1 / 2 == 0);
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/* Compute intervening leap days correctly even if year is negative.
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Take care to avoid int overflow. time_t overflow is OK, since
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only the low order bits of the correct time_t answer are needed.
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Don't convert to time_t until after all divisions are done, since
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time_t might be unsigned. */
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int a4 = (year >> 2) + (TM_YEAR_BASE >> 2) - ! (year & 3);
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int b4 = (tp->tm_year >> 2) + (TM_YEAR_BASE >> 2) - ! (tp->tm_year & 3);
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int a100 = a4 / 25 - (a4 % 25 < 0);
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int b100 = b4 / 25 - (b4 % 25 < 0);
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int a400 = a100 >> 2;
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int b400 = b100 >> 2;
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int intervening_leap_days = (a4 - b4) - (a100 - b100) + (a400 - b400);
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time_t years = year - (time_t) tp->tm_year;
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time_t days = (365 * years + intervening_leap_days
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+ (yday - tp->tm_yday));
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return (60 * (60 * (24 * days + (hour - tp->tm_hour))
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+ (min - tp->tm_min))
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+ (sec - tp->tm_sec));
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}
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}
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/* Use CONVERT to convert *T to a broken down time in *TP.
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If *T is out of range for conversion, adjust it so that
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it is the nearest in-range value and then convert that. */
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static struct tm *
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ranged_convert (struct tm *(*convert) (const time_t *, struct tm *),
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time_t *t, struct tm *tp)
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{
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struct tm *r;
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if (! (r = (*convert) (t, tp)) && *t)
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{
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time_t bad = *t;
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time_t ok = 0;
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struct tm tm;
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/* BAD is a known unconvertible time_t, and OK is a known good one.
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Use binary search to narrow the range between BAD and OK until
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they differ by 1. */
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while (bad != ok + (bad < 0 ? -1 : 1))
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{
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time_t mid = *t = (bad < 0
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? bad + ((ok - bad) >> 1)
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: ok + ((bad - ok) >> 1));
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if ((r = (*convert) (t, tp)))
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{
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tm = *r;
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ok = mid;
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}
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else
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bad = mid;
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}
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if (!r && ok)
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{
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/* The last conversion attempt failed;
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revert to the most recent successful attempt. */
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*t = ok;
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*tp = tm;
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r = tp;
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}
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}
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return r;
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}
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/* Convert *TP to a time_t value, inverting
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the monotonic and mostly-unit-linear conversion function CONVERT.
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Use *OFFSET to keep track of a guess at the offset of the result,
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compared to what the result would be for UTC without leap seconds.
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If *OFFSET's guess is correct, only one CONVERT call is needed. */
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time_t
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__mktime_internal (struct tm *tp,
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struct tm *(*convert) (const time_t *, struct tm *),
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time_t *offset)
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{
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time_t t, dt, t0, t1, t2;
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struct tm tm;
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/* The maximum number of probes (calls to CONVERT) should be enough
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to handle any combinations of time zone rule changes, solar time,
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leap seconds, and oscillations around a spring-forward gap.
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POSIX.1 prohibits leap seconds, but some hosts have them anyway. */
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int remaining_probes = 6;
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/* Time requested. Copy it in case CONVERT modifies *TP; this can
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occur if TP is localtime's returned value and CONVERT is localtime. */
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int sec = tp->tm_sec;
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int min = tp->tm_min;
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int hour = tp->tm_hour;
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int mday = tp->tm_mday;
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int mon = tp->tm_mon;
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int year_requested = tp->tm_year;
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int isdst = tp->tm_isdst;
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/* 1 if the previous probe was DST. */
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int dst2;
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/* Ensure that mon is in range, and set year accordingly. */
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int mon_remainder = mon % 12;
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int negative_mon_remainder = mon_remainder < 0;
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int mon_years = mon / 12 - negative_mon_remainder;
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int year = year_requested + mon_years;
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/* The other values need not be in range:
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the remaining code handles minor overflows correctly,
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assuming int and time_t arithmetic wraps around.
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Major overflows are caught at the end. */
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/* Calculate day of year from year, month, and day of month.
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The result need not be in range. */
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int yday = ((__mon_yday[__isleap (year + TM_YEAR_BASE)]
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[mon_remainder + 12 * negative_mon_remainder])
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+ mday - 1);
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int sec_requested = sec;
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/* Only years after 1970 are defined.
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If year is 69, it might still be representable due to
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timezone differences. */
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if (year < 69)
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return -1;
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#if LEAP_SECONDS_POSSIBLE
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/* Handle out-of-range seconds specially,
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since ydhms_tm_diff assumes every minute has 60 seconds. */
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if (sec < 0)
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sec = 0;
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if (59 < sec)
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sec = 59;
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#endif
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/* Invert CONVERT by probing. First assume the same offset as last time.
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Then repeatedly use the error to improve the guess. */
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tm.tm_year = EPOCH_YEAR - TM_YEAR_BASE;
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tm.tm_yday = tm.tm_hour = tm.tm_min = tm.tm_sec = 0;
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t0 = ydhms_tm_diff (year, yday, hour, min, sec, &tm);
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for (t = t1 = t2 = t0 + *offset, dst2 = 0;
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(dt = ydhms_tm_diff (year, yday, hour, min, sec,
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ranged_convert (convert, &t, &tm)));
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t1 = t2, t2 = t, t += dt, dst2 = tm.tm_isdst != 0)
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if (t == t1 && t != t2
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&& (tm.tm_isdst < 0
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|| (isdst < 0
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? dst2 <= (tm.tm_isdst != 0)
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: (isdst != 0) != (tm.tm_isdst != 0))))
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/* We can't possibly find a match, as we are oscillating
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between two values. The requested time probably falls
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within a spring-forward gap of size DT. Follow the common
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practice in this case, which is to return a time that is DT
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away from the requested time, preferring a time whose
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tm_isdst differs from the requested value. (If no tm_isdst
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was requested and only one of the two values has a nonzero
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tm_isdst, prefer that value.) In practice, this is more
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useful than returning -1. */
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break;
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else if (--remaining_probes == 0)
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return -1;
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/* If we have a match, check whether tm.tm_isdst has the requested
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value, if any. */
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if (dt == 0 && isdst != tm.tm_isdst && 0 <= isdst && 0 <= tm.tm_isdst)
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{
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/* tm.tm_isdst has the wrong value. Look for a neighboring
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time with the right value, and use its UTC offset.
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Heuristic: probe the previous three calendar quarters (approximately),
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looking for the desired isdst. This isn't perfect,
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but it's good enough in practice. */
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int quarter = 7889238; /* seconds per average 1/4 Gregorian year */
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int i;
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/* If we're too close to the time_t limit, look in future quarters. */
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if (t < TIME_T_MIN + 3 * quarter)
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quarter = -quarter;
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for (i = 1; i <= 3; i++)
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{
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time_t ot = t - i * quarter;
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struct tm otm;
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ranged_convert (convert, &ot, &otm);
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if (otm.tm_isdst == isdst)
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{
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/* We found the desired tm_isdst.
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Extrapolate back to the desired time. */
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t = ot + ydhms_tm_diff (year, yday, hour, min, sec, &otm);
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ranged_convert (convert, &t, &tm);
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break;
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}
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}
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}
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*offset = t - t0;
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#if LEAP_SECONDS_POSSIBLE
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if (sec_requested != tm.tm_sec)
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{
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/* Adjust time to reflect the tm_sec requested, not the normalized value.
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Also, repair any damage from a false match due to a leap second. */
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t += sec_requested - sec + (sec == 0 && tm.tm_sec == 60);
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if (! (*convert) (&t, &tm))
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return -1;
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}
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#endif
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if (TIME_T_MAX / INT_MAX / 366 / 24 / 60 / 60 < 3)
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{
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/* time_t isn't large enough to rule out overflows in ydhms_tm_diff,
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so check for major overflows. A gross check suffices,
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since if t has overflowed, it is off by a multiple of
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TIME_T_MAX - TIME_T_MIN + 1. So ignore any component of
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the difference that is bounded by a small value. */
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double dyear = (double) year_requested + mon_years - tm.tm_year;
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double dday = 366 * dyear + mday;
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double dsec = 60 * (60 * (24 * dday + hour) + min) + sec_requested;
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/* On Irix4.0.5 cc, dividing TIME_T_MIN by 3 does not produce
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correct results, ie., it erroneously gives a positive value
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of 715827882. Setting a variable first then doing math on it
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seems to work. (ghazi@caip.rutgers.edu) */
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const time_t time_t_max = TIME_T_MAX;
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const time_t time_t_min = TIME_T_MIN;
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if (time_t_max / 3 - time_t_min / 3 < (dsec < 0 ? - dsec : dsec))
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return -1;
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}
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if (year == 69)
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{
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/* If year was 69, need to check whether the time was representable
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or not. */
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if (t < 0 || t > 2 * 24 * 60 * 60)
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return -1;
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}
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*tp = tm;
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return t;
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}
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static time_t localtime_offset;
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/* Convert *TP to a time_t value. */
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time_t
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mktime (struct tm *tp)
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{
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#ifdef _LIBC
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/* POSIX.1 8.1.1 requires that whenever mktime() is called, the
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time zone names contained in the external variable `tzname' shall
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be set as if the tzset() function had been called. */
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__tzset ();
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#endif
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return __mktime_internal (tp, __localtime_r, &localtime_offset);
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}
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#ifdef weak_alias
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weak_alias (mktime, timelocal)
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#endif
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#ifdef _LIBC
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libc_hidden_def (mktime)
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libc_hidden_weak (timelocal)
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#endif
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#if DEBUG
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static int
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not_equal_tm (const struct tm *a, const struct tm *b)
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{
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return ((a->tm_sec ^ b->tm_sec)
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| (a->tm_min ^ b->tm_min)
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| (a->tm_hour ^ b->tm_hour)
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| (a->tm_mday ^ b->tm_mday)
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| (a->tm_mon ^ b->tm_mon)
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| (a->tm_year ^ b->tm_year)
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| (a->tm_mday ^ b->tm_mday)
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| (a->tm_yday ^ b->tm_yday)
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| (a->tm_isdst ^ b->tm_isdst));
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}
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static void
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print_tm (const struct tm *tp)
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{
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if (tp)
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printf ("%04d-%02d-%02d %02d:%02d:%02d yday %03d wday %d isdst %d",
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tp->tm_year + TM_YEAR_BASE, tp->tm_mon + 1, tp->tm_mday,
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tp->tm_hour, tp->tm_min, tp->tm_sec,
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tp->tm_yday, tp->tm_wday, tp->tm_isdst);
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else
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printf ("0");
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}
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static int
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check_result (time_t tk, struct tm tmk, time_t tl, const struct tm *lt)
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{
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if (tk != tl || !lt || not_equal_tm (&tmk, lt))
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{
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printf ("mktime (");
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print_tm (lt);
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printf (")\nyields (");
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print_tm (&tmk);
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printf (") == %ld, should be %ld\n", (long int) tk, (long int) tl);
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return 1;
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}
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return 0;
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}
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int
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main (int argc, char **argv)
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{
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int status = 0;
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struct tm tm, tmk, tml;
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struct tm *lt;
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time_t tk, tl, tl1;
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char trailer;
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if ((argc == 3 || argc == 4)
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&& (sscanf (argv[1], "%d-%d-%d%c",
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&tm.tm_year, &tm.tm_mon, &tm.tm_mday, &trailer)
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== 3)
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&& (sscanf (argv[2], "%d:%d:%d%c",
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&tm.tm_hour, &tm.tm_min, &tm.tm_sec, &trailer)
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== 3))
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{
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tm.tm_year -= TM_YEAR_BASE;
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tm.tm_mon--;
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tm.tm_isdst = argc == 3 ? -1 : atoi (argv[3]);
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tmk = tm;
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tl = mktime (&tmk);
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lt = localtime (&tl);
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if (lt)
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{
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tml = *lt;
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lt = &tml;
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}
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printf ("mktime returns %ld == ", (long int) tl);
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print_tm (&tmk);
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printf ("\n");
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status = check_result (tl, tmk, tl, lt);
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}
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else if (argc == 4 || (argc == 5 && strcmp (argv[4], "-") == 0))
|
||
{
|
||
time_t from = atol (argv[1]);
|
||
time_t by = atol (argv[2]);
|
||
time_t to = atol (argv[3]);
|
||
|
||
if (argc == 4)
|
||
for (tl = from; by < 0 ? to <= tl : tl <= to; tl = tl1)
|
||
{
|
||
lt = localtime (&tl);
|
||
if (lt)
|
||
{
|
||
tmk = tml = *lt;
|
||
tk = mktime (&tmk);
|
||
status |= check_result (tk, tmk, tl, &tml);
|
||
}
|
||
else
|
||
{
|
||
printf ("localtime (%ld) yields 0\n", (long int) tl);
|
||
status = 1;
|
||
}
|
||
tl1 = tl + by;
|
||
if ((tl1 < tl) != (by < 0))
|
||
break;
|
||
}
|
||
else
|
||
for (tl = from; by < 0 ? to <= tl : tl <= to; tl = tl1)
|
||
{
|
||
/* Null benchmark. */
|
||
lt = localtime (&tl);
|
||
if (lt)
|
||
{
|
||
tmk = tml = *lt;
|
||
tk = tl;
|
||
status |= check_result (tk, tmk, tl, &tml);
|
||
}
|
||
else
|
||
{
|
||
printf ("localtime (%ld) yields 0\n", (long int) tl);
|
||
status = 1;
|
||
}
|
||
tl1 = tl + by;
|
||
if ((tl1 < tl) != (by < 0))
|
||
break;
|
||
}
|
||
}
|
||
else
|
||
printf ("Usage:\
|
||
\t%s YYYY-MM-DD HH:MM:SS [ISDST] # Test given time.\n\
|
||
\t%s FROM BY TO # Test values FROM, FROM+BY, ..., TO.\n\
|
||
\t%s FROM BY TO - # Do not test those values (for benchmark).\n",
|
||
argv[0], argv[0], argv[0]);
|
||
|
||
return status;
|
||
}
|
||
|
||
#endif /* DEBUG */
|
||
|
||
/*
|
||
Local Variables:
|
||
compile-command: "gcc -DDEBUG -DHAVE_TIME_R_POSIX -Wall -W -O -g mktime.c -o mktime"
|
||
End:
|
||
*/
|