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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