lib/libc/time/difftime.c

   1 /*      $NetBSD: difftime.c,v 1.11 2012/03/20 16:39:08 matt 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 1.11 2012/03/20 16:39:08 matt 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(const time_t time1, const time_t time0)
  23 {
  24         /*
  25         ** If (sizeof (double) > sizeof (time_t)) simply convert and subtract
  26         ** (assuming that the larger type has more precision).
  27         ** This is the common real-world case circa 2004.
  28         */
  29 /* LINTED constant */
  30         if (sizeof (double) > sizeof (time_t))
  31                 return (double) time1 - (double) time0;
  32 /* LINTED constant */
  33         if (!TYPE_INTEGRAL(time_t)) {
  34                 /*
  35                 ** time_t is floating.
  36                 */
  37                 return time1 - time0;
  38         }
  39 /* LINTED constant */
  40         if (!TYPE_SIGNED(time_t)) {
  41                 /*
  42                 ** time_t is integral and unsigned.
  43                 ** The difference of two unsigned values can't overflow
  44                 ** if the minuend is greater than or equal to the subtrahend.
  45                 */
  46                 if (time1 >= time0)
  47                         return time1 - time0;
  48                 else    return -((double) (time0 - time1));
  49         }
  50         /*
  51         ** time_t is integral and signed.
  52         ** Handle cases where both time1 and time0 have the same sign
  53         ** (meaning that their difference cannot overflow).
  54         */
  55         if ((time1 < 0) == (time0 < 0))
  56                 return time1 - time0;
  57         /*
  58         ** time1 and time0 have opposite signs.
  59         ** Punt if unsigned long is too narrow.
  60         */
  61 /* CONSTCOND */
  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
  74 #if defined(__minix) && defined(__weak_alias)
  75 __weak_alias(difftime, __difftime50)
  76 #endif