lib/libc/time/difftime.c

   1 /*      $NetBSD: difftime.c,v 1.10 2009/12/31 22:49:16 mlelstv Exp $    */
   2
   3 /*
   4 ** This file is in the public domain, so clarified as of
   5 ** 1996-06-05 by Arthur David Olson.
   6 */
   7
   8 #include <sys/cdefs.h>
   9 #if defined(LIBC_SCCS) && !defined(lint)
  10 #if 0
  11 static char     elsieid[] = "@(#)difftime.c     8.1";
  12 #else
  13 __RCSID("$NetBSD: difftime.c,v 1.10 2009/12/31 22:49:16 mlelstv Exp $");
  14 #endif
  15 #endif /* LIBC_SCCS and not lint */
  16
  17 /*LINTLIBRARY*/
  18
  19 #include "private.h"    /* for time_t, TYPE_INTEGRAL, and TYPE_SIGNED */
  20
  21 double
  22 difftime(time1, time0)
  23 const time_t    time1;
  24 const time_t    time0;
  25 {
  26         /*
  27         ** If (sizeof (double) > sizeof (time_t)) simply convert and subtract
  28         ** (assuming that the larger type has more precision).
  29         ** This is the common real-world case circa 2004.
  30         */
  31 /* LINTED constant */
  32         if (sizeof (double) > sizeof (time_t))
  33                 return (double) time1 - (double) time0;
  34 /* LINTED constant */
  35         if (!TYPE_INTEGRAL(time_t)) {
  36                 /*
  37                 ** time_t is floating.
  38                 */
  39                 return time1 - time0;
  40         }
  41 /* LINTED constant */
  42         if (!TYPE_SIGNED(time_t)) {
  43                 /*
  44                 ** time_t is integral and unsigned.
  45                 ** The difference of two unsigned values can't overflow
  46                 ** if the minuend is greater than or equal to the subtrahend.
  47                 */
  48                 if (time1 >= time0)
  49                         return time1 - time0;
  50                 else    return -((double) (time0 - time1));
  51         }
  52         /*
  53         ** time_t is integral and signed.
  54         ** Handle cases where both time1 and time0 have the same sign
  55         ** (meaning that their difference cannot overflow).
  56         */
  57         if ((time1 < 0) == (time0 < 0))
  58                 return time1 - time0;
  59         /*
  60         ** time1 and time0 have opposite signs.
  61         ** Punt if unsigned long is too narrow.
  62         */
  63 /* CONSTCOND */
  64         if (sizeof (unsigned long) < sizeof (time_t))
  65                 return (double) time1 - (double) time0;
  66         /*
  67         ** Stay calm...decent optimizers will eliminate the complexity below.
  68         */
  69         if (time1 >= 0 /* && time0 < 0 */)
  70                 return (unsigned long) time1 +
  71                         (unsigned long) (-(time0 + 1)) + 1;
  72         return -(double) ((unsigned long) time0 +
  73                 (unsigned long) (-(time1 + 1)) + 1);
  74 }