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/*++
/* NAME
/* timecmp 3
/* SUMMARY
/* compare two time_t values
/* SYNOPSIS
/* #include <timecmp.h>
/*
/* int timecmp(t1, t2)
/* time_t t1;
/* time_t t2;
/* DESCRIPTION
/* The timecmp() function return an integer greater than, equal to, or
/* less than 0, according as the time t1 is greater than, equal to, or
/* less than the time t2. The comparison is made in a manner that is
/* insensitive to clock wrap-around, provided the underlying times are
/* within half of the time interval between the smallest and largest
/* representable time values.
/* LICENSE
/* .ad
/* .fi
/* The Secure Mailer license must be distributed with this software.
/* AUTHOR(S)
/* Wietse Venema
/* IBM T.J. Watson Research
/* P.O. Box 704
/* Yorktown Heights, NY 10598, USA
/*
/* Viktor Dukhovni
/*--*/
#include "timecmp.h"
/* timecmp - wrap-safe time_t comparison */
int timecmp(time_t t1, time_t t2)
{
time_t delta = t1 - t2;
if (delta == 0)
return 0;
#define UNSIGNED(type) ( ((type)-1) > ((type)0) )
/*
* With a constant switch value, the compiler will emit only the code for
* the correct case, so the signed/unsigned test happens at compile time.
*/
switch (UNSIGNED(time_t) ? 0 : 1) {
case 0:
return ((2 * delta > delta) ? 1 : -1);
case 1:
return ((delta > (time_t) 0) ? 1 : -1);
}
}
#ifdef TEST
#include <assert.h>
/*
* Bit banging!! There is no official constant that defines the INT_MAX
* equivalent of the off_t type. Wietse came up with the following macro
* that works as long as off_t is some two's complement number.
*
* Note, however, that C99 permits signed integer representations other than
* two's complement.
*/
#include <limits.h>
#define __MAXINT__(T) ((T) (((((T) 1) << ((sizeof(T) * CHAR_BIT) - 1)) ^ ((T) -1))))
int main(void)
{
time_t now = time((time_t *) 0);
/* Test that it works for normal times */
assert(timecmp(now + 10, now) > 0);
assert(timecmp(now, now) == 0);
assert(timecmp(now - 10, now) < 0);
/* Test that it works at a boundary time */
if (UNSIGNED(time_t))
now = (time_t) -1;
else
now = __MAXINT__(time_t);
assert(timecmp(now + 10, now) > 0);
assert(timecmp(now, now) == 0);
assert(timecmp(now - 10, now) < 0);
return (0);
}
#endif
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