stdtime/FreeBSD/difftime.c

   1 /*
   2 ** This file is in the public domain, so clarified as of
   3 ** 1996-06-05 by Arthur David Olson.
   4 */
   5
   6 #pragma clang diagnostic push
   7 #pragma clang diagnostic ignored "-Wunreachable-code"
   8
   9 #include <sys/cdefs.h>
  10 #ifndef lint
  11 #ifndef NOID
  12 static char     elsieid[] __unused = "@(#)difftime.c    8.1";
  13 #endif /* !defined NOID */
  14 #endif /* !defined lint */
  15 __FBSDID("$FreeBSD: src/lib/libc/stdtime/difftime.c,v 1.9 2009/05/23 06:31:50 edwin Exp $");
  16
  17 /*LINTLIBRARY*/
  18
  19 #include "namespace.h"
  20 #include "private.h"    /* for time_t, TYPE_INTEGRAL, and TYPE_SIGNED */
  21 #include "un-namespace.h"
  22
  23 double
  24 difftime(time1, time0)
  25 const time_t    time1;
  26 const time_t    time0;
  27 {
  28         /*
  29         ** If (sizeof (double) > sizeof (time_t)) simply convert and subtract
  30         ** (assuming that the larger type has more precision).
  31         ** This is the common real-world case circa 2004.
  32         */
  33         if (sizeof (double) > sizeof (time_t))
  34                 return (double) time1 - (double) time0;
  35         if (!TYPE_INTEGRAL(time_t)) {
  36                 /*
  37                 ** time_t is floating.
  38                 */
  39                 return time1 - time0;
  40         }
  41         if (!TYPE_SIGNED(time_t)) {
  42                 /*
  43                 ** time_t is integral and unsigned.
  44                 ** The difference of two unsigned values can't overflow
  45                 ** if the minuend is greater than or equal to the subtrahend.
  46                 */
  47                 if (time1 >= time0)
  48                         return time1 - time0;
  49                 else    return -((double) (time0 - time1));
  50         }
  51         /*
  52         ** time_t is integral and signed.
  53         ** Handle cases where both time1 and time0 have the same sign
  54         ** (meaning that their difference cannot overflow).
  55         */
  56         if ((time1 < 0) == (time0 < 0))
  57                 return time1 - time0;
  58         /*
  59         ** time1 and time0 have opposite signs.
  60         ** Punt if unsigned long is too narrow.
  61         */
  62         if (sizeof (unsigned long) < sizeof (time_t))
  63                 return (double) time1 - (double) time0;
  64         /*
  65         ** Stay calm...decent optimizers will eliminate the complexity below.
  66         */
  67         if (time1 >= 0 /* && time0 < 0 */)
  68                 return (unsigned long) time1 +
  69                         (unsigned long) (-(time0 + 1)) + 1;
  70         return -(double) ((unsigned long) time0 +
  71                 (unsigned long) (-(time1 + 1)) + 1);
  72 }
  73 #pragma clang diagnostic pop