gonzui

    1: /*      $OpenBSD: difftime.c,v 1.9 2005/08/08 08:05:38 espie Exp $ */
    2: /*
    3: ** This file is in the public domain, so clarified as of
    4: ** 1996-06-05 by Arthur David Olson.
    5: */
    6: 
    7: /*LINTLIBRARY*/
    8: #define TYPE_INTEGRAL(type) (((type) 0.5) != 0.5)
    9: #define TYPE_SIGNED(type) (((type) -1) < 0)
   10: #include <time.h>       /* for time_t, TYPE_INTEGRAL, and TYPE_SIGNED */
   11: 
   12: double
   13: difftime(time1, time0)
   14: const time_t    time1;
   15: const time_t    time0;
   16: {
   17:         /*
   18:         ** If (sizeof (double) > sizeof (time_t)) simply convert and subtract
   19:         ** (assuming that the larger type has more precision).
   20:         ** This is the common real-world case circa 2004.
   21:         */
   22:         if (sizeof (double) > sizeof (time_t))
   23:                 return (double) time1 - (double) time0;
   24:         if (!TYPE_INTEGRAL(time_t)) {
   25:                 /*
   26:                 ** time_t is floating.
   27:                 */
   28:                 return time1 - time0;
   29:         }
   30:         if (!TYPE_SIGNED(time_t)) {
   31:                 /*
   32:                 ** time_t is integral and unsigned.
   33:                 ** The difference of two unsigned values can't overflow
   34:                 ** if the minuend is greater than or equal to the subtrahend.
   35:                 */
   36:                 if (time1 >= time0)
   37:                         return time1 - time0;
   38:                 else  return -((double) (time0 - time1));
   39:         }
   40:         /*
   41:         ** time_t is integral and signed.
   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 unsigned long is too narrow.
   50:         */
   51:         if (sizeof (unsigned long) < sizeof (time_t))
   52:                 return (double) time1 - (double) time0;
   53:         /*
   54:         ** Stay calm...decent optimizers will eliminate the complexity below.
   55:         */
   56:         if (time1 >= 0 /* && time0 < 0 */)
   57:                 return (unsigned long) time1 +
   58:                         (unsigned long) (-(time0 + 1)) + 1;
   59:         return -(double) ((unsigned long) time0 +
   60:                 (unsigned long) (-(time1 + 1)) + 1);
   61: }