For our individual projects, we are combining the skills we have learned thus far and attempting to make some improvements to the C libraries we all use everyday. The C code that I will be attempting to analyze and create optimizations for is:
mktime.c
The purpose of mktime.c is to "Convert a 'struct tm' to a time_t value".
In other words, time_t is the computer's tracking of time in seconds that has transpired since January 1, 1970. Since this number would be a very large number of seconds, most humans cannot easily convert a given date into time_t. Thus, humans would write something like
March 10, 2017, and mktime.c would take that human language for the date (struct tm) and convert it into the amount of seconds from the beginning of computer time until now.
The reason why I decided to look into this function is because I use functions concerning 'time' for most of my own projects. I also thought that I wanted to take a crack at a function that would be used quite often by programmers everywhere and make a real contribution. The mktime.c function was fairly long, so I thought I would probably find SOMETHING I could make better inside all that code.
Below I will display the entire function for mktime.c and highlight some of the lines of code that look like I could possibly do something optimal with.
----------------------------------------------
/* Convert a 'struct tm' to a time_t value.
Copyright (C) 1993-2017 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Paul Eggert <eggert@twinsun.com>.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 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
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
/* Define this to have a standalone program to test this implementation of
mktime. */
/* #define DEBUG_MKTIME 1 */
#ifndef _LIBC
# include <config.h>
#endif
/* Assume that leap seconds are possible, unless told otherwise.
If the host has a 'zic' command with a '-L leapsecondfilename' option,
then it supports leap seconds; otherwise it probably doesn't. */
#ifndef LEAP_SECONDS_POSSIBLE
# define LEAP_SECONDS_POSSIBLE 1
#endif
#include <time.h>
#include <limits.h>
#include <string.h>
/* For the real memcpy prototype. */
#if defined DEBUG_MKTIME && DEBUG_MKTIME
# include <stdio.h>
# include <stdlib.h>
/* Make it work even if the system's libc has its own mktime routine. */
# undef mktime
# define mktime my_mktime
#endif /* DEBUG_MKTIME */
/* Some of the code in this file assumes that signed integer overflow
silently wraps around. This assumption can't easily be programmed
around, nor can it be checked for portably at compile-time or
easily eliminated at run-time.
Define WRAPV to 1 if the assumption is valid and if
#pragma GCC optimize ("wrapv")
does not trigger GCC bug 51793
<http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51793>.
Otherwise, define it to 0; this forces the use of slower code that,
while not guaranteed by the C Standard, works on all production
platforms that we know about. */
#ifndef WRAPV
# if (((__GNUC__ == 4 && 4 <= __GNUC_MINOR__) || 4 < __GNUC__) \
&& defined __GLIBC__)
# pragma GCC optimize ("wrapv")
# define WRAPV 1
# else
# define WRAPV 0
# endif
#endif
/* Verify a requirement at compile-time (unlike assert, which is runtime). */
#define verify(name, assertion) struct name { char a[(assertion) ? 1 : -1]; }
/* A signed type that is at least one bit wider than int. */
#if INT_MAX <= LONG_MAX / 2
typedef long int long_int;
#else
typedef long long int long_int;
#endif
verify (long_int_is_wide_enough, INT_MAX == INT_MAX * (long_int) 2 / 2);
/* Shift A right by B bits portably, by dividing A by 2**B and
truncating towards minus infinity. A and B should be free of side
effects, and B should be in the range 0 <= B <= INT_BITS - 2, where
INT_BITS is the number of useful bits in an int. GNU code can
assume that INT_BITS is at least 32.
ISO C99 says that A >> B is implementation-defined if A < 0. Some
implementations (e.g., UNICOS 9.0 on a Cray Y-MP EL) don't shift
right in the usual way when A < 0, so SHR falls back on division if
ordinary A >> B doesn't seem to be the usual signed shift. */
#define SHR(a, b) \
((-1 >> 1 == -1 \
&& (long_int) -1 >> 1 == -1 \
&& ((time_t) -1 >> 1 == -1 || ! TYPE_SIGNED (time_t))) \ CODE USED OFTEN!!
? (a) >> (b) \
: (a) / (1 << (b)) - ((a) % (1 << (b)) < 0))
/* The extra casts in the following macros work around compiler bugs,
e.g., in Cray C 5.0.3.0. */
/* True if the arithmetic type T is an integer type. bool counts as
an integer. */
#define TYPE_IS_INTEGER(t) ((t) 1.5 == 1)
/* True if negative values of the signed integer type T use two's
complement, or if T is an unsigned integer type. */
#define TYPE_TWOS_COMPLEMENT(t) ((t) ~ (t) 0 == (t) -1)
/* True if the arithmetic type T is signed. */
#define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
/* The maximum and minimum values for the integer type T. These
macros have undefined behavior if T is signed and has padding bits.
If this is a problem for you, please let us know how to fix it for
your host. */
#define TYPE_MINIMUM(t) \
((t) (! TYPE_SIGNED (t) \
? (t) 0 \
: ~ TYPE_MAXIMUM (t)))
#define TYPE_MAXIMUM(t) \
((t) (! TYPE_SIGNED (t) \
? (t) -1 \
: ((((t) 1 << (sizeof (t) * CHAR_BIT - 2)) - 1) * 2 + 1))) STRENGTH REDUCTION?
#ifndef TIME_T_MIN
# define TIME_T_MIN TYPE_MINIMUM (time_t)
#endif
#ifndef TIME_T_MAX
# define TIME_T_MAX TYPE_MAXIMUM (time_t)
#endif
#define TIME_T_MIDPOINT (SHR (TIME_T_MIN + TIME_T_MAX, 1) + 1)
verify (time_t_is_integer, TYPE_IS_INTEGER (time_t));
verify (twos_complement_arithmetic,
(TYPE_TWOS_COMPLEMENT (int)
&& TYPE_TWOS_COMPLEMENT (long_int)
&& TYPE_TWOS_COMPLEMENT (time_t)));
#define EPOCH_YEAR 1970
#define TM_YEAR_BASE 1900
verify (base_year_is_a_multiple_of_100, TM_YEAR_BASE % 100 == 0);
/* Return 1 if YEAR + TM_YEAR_BASE is a leap year. */
static int
leapyear (long_int year)
{
/* Don't add YEAR to TM_YEAR_BASE, as that might overflow.
Also, work even if YEAR is negative. */
return
((year & 3) == 0
&& (year % 100 != 0
|| ((year / 100) & 3) == (- (TM_YEAR_BASE / 100) & 3)));
}
/* How many days come before each month (0-12). */
#ifndef _LIBC
static
#endif
const unsigned short int
__mon_yday[2][13] =
COMBINE INTO SINGLE ARRAY?
{
/* Normal years. */
{ 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 },
/* Leap years. */
{ 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 }
};
#ifndef _LIBC
/* Portable standalone applications should supply a <time.h> that
declares a POSIX-compliant localtime_r, for the benefit of older
implementations that lack localtime_r or have a nonstandard one.
See the gnulib time_r module for one way to implement this. */
# undef __localtime_r
# define __localtime_r localtime_r
# define __mktime_internal mktime_internal
# include "mktime-internal.h"
#endif
/* Return 1 if the values A and B differ according to the rules for
tm_isdst: A and B differ if one is zero and the other positive. */
static int
isdst_differ (int a, int b)
{
return (!a != !b) && (0 <= a) && (0 <= b);
}
/* Return an integer value measuring (YEAR1-YDAY1 HOUR1:MIN1:SEC1) -
(YEAR0-YDAY0 HOUR0:MIN0:SEC0) in seconds, assuming that the clocks
were not adjusted between the time stamps.
The YEAR values uses the same numbering as TP->tm_year. Values
need not be in the usual range. However, YEAR1 must not be less
than 2 * INT_MIN or greater than 2 * INT_MAX.
The result may overflow. It is the caller's responsibility to
detect overflow. */
static time_t
ydhms_diff (long_int year1, long_int yday1, int hour1, int min1, int sec1,
int year0, int yday0, int hour0, int min0, int sec0)
{
verify (C99_integer_division,
-1 / 2 == 0);
PRECALCULATE TO -0.5 ?
/* Compute intervening leap days correctly even if year is negative.
Take care to avoid integer overflow here. */
int a4 = SHR (year1, 2) + SHR
(TM_YEAR_BASE, 2) - ! (year1 & 3); REPETITIOUS,
int b4 = SHR (year0, 2) + SHR
(TM_YEAR_BASE, 2) - ! (year0 & 3); USE CONSTANTS?
int a100 = a4 / 25 - (a4 % 25 < 0);
int b100 = b4 / 25 - (b4 % 25 < 0); STRENGTH REDUCTIONS?
int a400 = SHR (a100, 2);
int b400 = SHR (b100, 2);
int intervening_leap_days = (a4 - b4) - (a100 - b100) + (a400 - b400);
/* Compute the desired time in time_t precision. Overflow might
occur here. */
time_t tyear1 = year1;
time_t years = tyear1 - year0;
time_t days = 365 * years + yday1 - yday0 + intervening_leap_days;
time_t hours = 24 * days + hour1 - hour0;
time_t minutes = 60 * hours + min1 - min0;
time_t seconds = 60 * minutes + sec1 - sec0;
return seconds;
}
/* Return the average of A and B, even if A + B would overflow. */
static time_t
time_t_avg (time_t a, time_t b)
{
return SHR (a, 1) + SHR (b, 1) + (a & b & 1);
}
/* Return 1 if A + B does not overflow. If time_t is unsigned and if
B's top bit is set, assume that the sum represents A - -B, and
return 1 if the subtraction does not wrap around. */
static int
time_t_add_ok (time_t a, time_t b)
{
if (! TYPE_SIGNED (time_t))
{
time_t sum = a + b;
return (sum < a) == (TIME_T_MIDPOINT <= b);
}
else if (WRAPV)
{
time_t sum = a + b;
return (sum < a) == (b < 0);
}
else
{
time_t avg =
time_t_avg (a, b); INLINING?
return
TIME_T_MIN / 2 <= avg && avg <=
TIME_T_MAX / 2;
MAX * 0.5 ?
}
}
/* Return 1 if A + B does not overflow. */
static int
time_t_int_add_ok (time_t a, int b)
{
verify (int_no_wider_than_time_t, INT_MAX <= TIME_T_MAX);
if (WRAPV)
{
time_t sum = a + b;
return (sum < a) == (b < 0);
}
else
{
int a_odd = a & 1;
time_t avg = SHR (a, 1) + (SHR (b, 1) + (a_odd & b));
return
TIME_T_MIN / 2 <= avg && avg <=
TIME_T_MAX / 2;
}
}
/* Return a time_t value corresponding to (YEAR-YDAY HOUR:MIN:SEC),
assuming that *T corresponds to *TP and that no clock adjustments
occurred between *TP and the desired time.
If TP is null, return a value not equal to *T; this avoids false matches.
If overflow occurs, yield the minimal or maximal value, except do not
yield a value equal to *T. */
static time_t
guess_time_tm (long_int year, long_int yday, int hour, int min, int sec,
const time_t *t, const struct tm *tp)
{
if (tp)
{
time_t d = ydhms_diff (year, yday, hour, min, sec,
tp->tm_year, tp->tm_yday,
tp->tm_hour, tp->tm_min, tp->tm_sec);
if (time_t_add_ok (*t, d))
return *t + d;
}
/* Overflow occurred one way or another. Return the nearest result
that is actually in range, except don't report a zero difference
if the actual difference is nonzero, as that would cause a false
match; and don't oscillate between two values, as that would
confuse the spring-forward gap detector. */
return (*t < TIME_T_MIDPOINT
? (*t <= TIME_T_MIN + 1 ? *t + 1 : TIME_T_MIN)
: (TIME_T_MAX - 1 <= *t ? *t - 1 : TIME_T_MAX));
}
/* Use CONVERT to convert *T to a broken down time in *TP.
If *T is out of range for conversion, adjust it so that
it is the nearest in-range value and then convert that. */
static struct tm *
ranged_convert (struct tm *(*convert) (const time_t *, struct tm *),
time_t *t, struct tm *tp)
{
struct tm *r =
convert (t, tp);
INLINING?
if (!r && *t) SHORT-CIRCUIT EVALUATION(&&)
{
time_t bad = *t;
time_t ok = 0;
/* BAD is a known unconvertible time_t, and OK is a known good one.
Use binary search to narrow the range between BAD and OK until
they differ by 1. */
while (bad != ok + (bad < 0 ? -1 : 1))
{
time_t mid = *t = time_t_avg (ok, bad);
r = convert (t, tp);
if (r)
ok = mid;
else
bad = mid;
}
if (!r && ok)
{
/* The last conversion attempt failed;
revert to the most recent successful attempt. */
*t = ok;
r = convert (t, tp);
}
}
return r;
}
/* Convert *TP to a time_t value, inverting
the monotonic and mostly-unit-linear conversion function CONVERT.
Use *OFFSET to keep track of a guess at the offset of the result,
compared to what the result would be for UTC without leap seconds.
If *OFFSET's guess is correct, only one CONVERT call is needed.
This function is external because it is used also by timegm.c. */
time_t
__mktime_internal (struct tm *tp,
struct tm *(*convert) (const time_t *, struct tm *),
time_t *offset)
{
time_t t, gt, t0, t1, t2;
struct tm tm;
/* The maximum number of probes (calls to CONVERT) should be enough
to handle any combinations of time zone rule changes, solar time,
leap seconds, and oscillations around a spring-forward gap.
POSIX.1 prohibits leap seconds, but some hosts have them anyway. */
int remaining_probes = 6;
/* Time requested. Copy it in case CONVERT modifies *TP; this can
occur if TP is localtime's returned value and CONVERT is localtime. */
int sec = tp->tm_sec;
int min = tp->tm_min;
int hour = tp->tm_hour;
int mday = tp->tm_mday;
int mon = tp->tm_mon;
int year_requested = tp->tm_year;
int isdst = tp->tm_isdst;
/* 1 if the previous probe was DST. */
int dst2;
/* Ensure that mon is in range, and set year accordingly. */
int mon_remainder = mon % 12;
int negative_mon_remainder = mon_remainder < 0;
int mon_years = mon / 12 - negative_mon_remainder;
long_int lyear_requested = year_requested;
long_int year = lyear_requested + mon_years;
/* The other values need not be in range:
the remaining code handles minor overflows correctly,
assuming int and time_t arithmetic wraps around.
Major overflows are caught at the end. */
/* Calculate day of year from year, month, and day of month.
The result need not be in range. */
int mon_yday = ((__mon_yday[leapyear (year)]
[mon_remainder + 12 * negative_mon_remainder])
- 1);
long_int lmday = mday;
long_int yday = mon_yday + lmday;
time_t guessed_offset = *offset;
int sec_requested = sec;
if (LEAP_SECONDS_POSSIBLE)
{
/* Handle out-of-range seconds specially,
since ydhms_tm_diff assumes every minute has 60 seconds. */
if (sec < 0)
sec = 0;
if (59 < sec)
sec = 59;
}
/* Invert CONVERT by probing. First assume the same offset as last
time. */
t0 = ydhms_diff (year, yday, hour, min, sec,
EPOCH_YEAR - TM_YEAR_BASE, 0, 0, 0, - guessed_offset);
if (TIME_T_MAX / INT_MAX / 366 / 24 / 60 / 60 < 3) TOO MANY DIVISIONS, SIMPLIFY?
{
/* time_t isn't large enough to rule out overflows, so check
for major overflows. A gross check suffices, since if t0
has overflowed, it is off by a multiple of TIME_T_MAX -
TIME_T_MIN + 1. So ignore any component of the difference
that is bounded by a small value. */
/* Approximate log base 2 of the number of time units per
biennium. A biennium is 2 years; use this unit instead of
years to avoid integer overflow. For example, 2 average
Gregorian years are 2 * 365.2425 * 24 * 60 * 60 seconds,
which is 63113904 seconds, and rint (log2 (63113904)) is
26. */
int ALOG2_SECONDS_PER_BIENNIUM = 26;
int ALOG2_MINUTES_PER_BIENNIUM = 20;
int ALOG2_HOURS_PER_BIENNIUM = 14;
int ALOG2_DAYS_PER_BIENNIUM = 10;
int LOG2_YEARS_PER_BIENNIUM = 1;
int approx_requested_biennia =
(SHR (year_requested, LOG2_YEARS_PER_BIENNIUM)
- SHR (EPOCH_YEAR - TM_YEAR_BASE, LOG2_YEARS_PER_BIENNIUM)
+ SHR (mday, ALOG2_DAYS_PER_BIENNIUM)
+ SHR (hour, ALOG2_HOURS_PER_BIENNIUM)
+ SHR (min, ALOG2_MINUTES_PER_BIENNIUM)
+ (LEAP_SECONDS_POSSIBLE
? 0
: SHR (sec, ALOG2_SECONDS_PER_BIENNIUM)));
int approx_biennia = SHR (t0, ALOG2_SECONDS_PER_BIENNIUM);
int diff = approx_biennia - approx_requested_biennia;
int approx_abs_diff = diff < 0 ? -1 - diff : diff;
/* IRIX 4.0.5 cc miscalculates TIME_T_MIN / 3: it erroneously
gives a positive value of 715827882. Setting a variable
first then doing math on it seems to work.
(ghazi@caip.rutgers.edu) */
time_t time_t_max = TIME_T_MAX;
time_t time_t_min = TIME_T_MIN;
time_t overflow_threshold =
(time_t_max / 3 - time_t_min / 3) >> ALOG2_SECONDS_PER_BIENNIUM;
WHY NOT (MAX - MIN) / 3 ?? ... DIVIDING TWICE IS REDUNDANT
if (overflow_threshold < approx_abs_diff)
{
/* Overflow occurred. Try repairing it; this might work if
the time zone offset is enough to undo the overflow. */
time_t repaired_t0 = -1 - t0;
approx_biennia = SHR (repaired_t0, ALOG2_SECONDS_PER_BIENNIUM);
diff = approx_biennia - approx_requested_biennia;
approx_abs_diff = diff < 0 ? -1 - diff : diff;
if (overflow_threshold < approx_abs_diff)
return -1;
guessed_offset += repaired_t0 - t0;
t0 = repaired_t0;
}
}
/* Repeatedly use the error to improve the guess. */
for (t = t1 = t2 = t0, dst2 = 0;
(gt = guess_time_tm (year, yday, hour, min, sec, &t,
ranged_convert (convert, &t, &tm)),
t != gt);
t1 = t2, t2 = t, t = gt, dst2 = tm.tm_isdst != 0)
if (t == t1 && t != t2
&& (tm.tm_isdst < 0 SHORT-CIRCUIT EVALUATIONS
|| (isdst < 0
? dst2 <= (tm.tm_isdst != 0)
: (isdst != 0) != (tm.tm_isdst != 0))))
/* We can't possibly find a match, as we are oscillating
between two values. The requested time probably falls
within a spring-forward gap of size GT - T. Follow the common
practice in this case, which is to return a time that is GT - T
away from the requested time, preferring a time whose
tm_isdst differs from the requested value. (If no tm_isdst
was requested and only one of the two values has a nonzero
tm_isdst, prefer that value.) In practice, this is more
useful than returning -1. */
goto offset_found;
else if (--remaining_probes == 0)
return -1;
/* We have a match. Check whether tm.tm_isdst has the requested
value, if any. */
if (isdst_differ (isdst, tm.tm_isdst))
{
/* tm.tm_isdst has the wrong value. Look for a neighboring
time with the right value, and use its UTC offset.
Heuristic: probe the adjacent timestamps in both directions,
looking for the desired isdst. This should work for all real
time zone histories in the tz database. */
/* Distance between probes when looking for a DST boundary. In
tzdata2003a, the shortest period of DST is 601200 seconds
(e.g., America/Recife starting 2000-10-08 01:00), and the
shortest period of non-DST surrounded by DST is 694800
seconds (Africa/Tunis starting 1943-04-17 01:00). Use the
minimum of these two values, so we don't miss these short
periods when probing. */
int stride = 601200;
/* The longest period of DST in tzdata2003a is 536454000 seconds
(e.g., America/Jujuy starting 1946-10-01 01:00). The longest
period of non-DST is much longer, but it makes no real sense
to search for more than a year of non-DST, so use the DST
max. */
int
duration_max = 536454000;
/* Search in both directions, so the maximum distance is half
the duration; add the stride to avoid off-by-1 problems. */
int delta_bound =
duration_max / 2 + stride;
ALREADY HAVE CONSTANT! USE IT
int delta, direction;
for (delta = stride; delta < delta_bound; delta += stride)
for (
direction = -1; direction <= 1; direction += 2)
if (time_t_int_add_ok (t, delta * direction))
{
time_t ot = t + delta
* direction;
DIRECTION IS ONLY EVER -1 AND 1 ...
struct tm otm;
ranged_convert (convert, &ot, &otm);
if (! isdst_differ (isdst, otm.tm_isdst))
{
/* We found the desired tm_isdst.
Extrapolate back to the desired time. */
t = guess_time_tm (year, yday, hour, min, sec, &ot, &otm);
ranged_convert (convert, &t, &tm);
goto offset_found;
}
}
}
offset_found:
*offset = guessed_offset + t - t0;
if (LEAP_SECONDS_POSSIBLE && sec_requested != tm.tm_sec)
{
/* Adjust time to reflect the tm_sec requested, not the normalized value.
Also, repair any damage from a false match due to a leap second. */
int sec_adjustment = (sec == 0 && tm.tm_sec == 60) - sec;
if (! time_t_int_add_ok (t, sec_requested))
return -1;
t1 = t + sec_requested;
if (! time_t_int_add_ok (t1, sec_adjustment)) REPETITIVE-LOOKING... SIMPLIFY??
return -1;
t2 = t1 + sec_adjustment;
if (! convert (&t2, &tm))
return -1;
t = t2;
}
*tp = tm;
return t;
}
/* FIXME: This should use a signed type wide enough to hold any UTC
offset in seconds. 'int' should be good enough for GNU code. We
can't fix this unilaterally though, as other modules invoke
__mktime_internal. */
static time_t localtime_offset;
/* Convert *TP to a time_t value. */
time_t
mktime (struct tm *tp)
{
#ifdef _LIBC
/* POSIX.1 8.1.1 requires that whenever mktime() is called, the
time zone names contained in the external variable 'tzname' shall
be set as if the tzset() function had been called. */
__tzset ();
#endif
return __mktime_internal (tp, __localtime_r, &localtime_offset);
}
#ifdef weak_alias
weak_alias (mktime, timelocal)
#endif
#ifdef _LIBC
libc_hidden_def (mktime)
libc_hidden_weak (timelocal)
#endif
#if defined DEBUG_MKTIME && DEBUG_MKTIME
static int
not_equal_tm (const struct tm *a, const struct tm *b)
{
return ((a->tm_sec ^ b->tm_sec)
| (a->tm_min ^ b->tm_min)
| (a->tm_hour ^ b->tm_hour)
| (a->tm_mday ^ b->tm_mday)
| (a->tm_mon ^ b->tm_mon)
| (a->tm_year ^ b->tm_year)
| (a->tm_yday ^ b->tm_yday)
| isdst_differ (a->tm_isdst, b->tm_isdst));
}
static void
print_tm (const struct tm *tp)
{
if (tp)
printf ("%04d-%02d-%02d %02d:%02d:%02d yday %03d wday %d isdst %d",
tp->tm_year + TM_YEAR_BASE, tp->tm_mon + 1, tp->tm_mday,
tp->tm_hour, tp->tm_min, tp->tm_sec,
tp->tm_yday, tp->tm_wday, tp->tm_isdst);
else
printf ("0");
}
static int
check_result (time_t tk, struct tm tmk, time_t tl, const struct tm *lt)
{
if (tk != tl || !lt || not_equal_tm (&tmk, lt)) SHORT-CIRCUIT EVALUATIONS ( || )
{
printf ("mktime (");
print_tm (lt);
printf (")\nyields (");
print_tm (&tmk);
printf (") == %ld, should be %ld\n", (long int) tk, (long int) tl);
return 1;
}
return 0;
}
int
main (int argc, char **argv)
{
int status = 0;
struct tm tm, tmk, tml;
struct tm *lt;
time_t tk, tl, tl1;
char trailer;
if
((argc == 3 || argc == 4) (ARGC > 2 && ARGC < 5) POSSIBLY CHEAPER?
&& (sscanf (argv[1], "%d-%d-%d%c",
&tm.tm_year, &tm.tm_mon, &tm.tm_mday, &trailer)
== 3)
&& (sscanf (argv[2], "%d:%d:%d%c",
&tm.tm_hour, &tm.tm_min, &tm.tm_sec, &trailer)
== 3))
{
tm.tm_year -= TM_YEAR_BASE;
tm.tm_mon--;
tm.tm_isdst = argc == 3 ? -1 : atoi (argv[3]);
tmk = tm;
tl = mktime (&tmk);
lt = localtime (&tl);
if (lt)
{
tml = *lt;
lt = &tml;
}
printf ("mktime returns %ld == ", (long int) tl);
print_tm (&tmk);
printf ("\n");
status = check_result (tl, tmk, tl, lt);
}
else if
(argc == 4 || (argc == 5 && strcmp (argv[4], "-") == 0)) SHORT-CIRCUIT EVALUATION
{
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); INLINING??
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_MKTIME */
/*
Local Variables:
compile-command: "gcc -DDEBUG_MKTIME -I. -Wall -W -O2 -g mktime.c -o mktime"
End:
*/
-----------------------------------------
