lib/libc/time/difftime.c

   1 /*      $NetBSD: difftime.c,v 1.15 2013/09/20 19:06:54 christos 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 1.15 2013/09/20 19:06:54 christos Exp $");
  14 #endif
  15 #endif /* LIBC_SCCS and not lint */
  16
  17 /*LINTLIBRARY*/
  18
  19 #include "private.h"    /* for time_t and TYPE_SIGNED */
  20
  21 double ATTRIBUTE_CONST
  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         */
  28         /*CONSTCOND*/
  29         if (sizeof (double) > sizeof (time_t))
  30                 return (double) time1 - (double) time0;
  31         /*LINTED const not */
  32         if (!TYPE_SIGNED(time_t)) {
  33                 /*
  34                 ** The difference of two unsigned values can't overflow
  35                 ** if the minuend is greater than or equal to the subtrahend.
  36                 */
  37                 if (time1 >= time0)
  38                         return            time1 - time0;
  39                 else    return -(double) (time0 - time1);
  40         }
  41         /*
  42         ** Handle cases where both time1 and time0 have the same sign
  43         ** (meaning that their difference cannot overflow).
  44         */
  45         if ((time1 < 0) == (time0 < 0))
  46                 return time1 - time0;
  47         /*
  48         ** time1 and time0 have opposite signs.
  49         ** Punt if uintmax_t is too narrow.
  50         ** This suffers from double rounding; attempt to lessen that
  51         ** by using long double temporaries.
  52         */
  53         /* CONSTCOND */
  54         if (sizeof (uintmax_t) < sizeof (time_t))
  55                 return (double) time1 - (double) time0;
  56         /*
  57         ** Stay calm...decent optimizers will eliminate the complexity below.
  58         */
  59         if (time1 >= 0 /* && time0 < 0 */)
  60                 return    (uintmax_t) time1 + (uintmax_t) (-(time0 + 1)) + 1;
  61         return -(double) ((uintmax_t) time0 + (uintmax_t) (-(time1 + 1)) + 1);
  62 }