| /* |

| ** This file is in the public domain, so clarified as of |

| ** 1996-06-05 by Arthur David Olson. |

| */ |

| |

| #ifndef lint |

| #ifndef NOID |

| static char elsieid[] = "@(#)difftime.c 8.1"; |

| #endif /* !defined NOID */ |

| #endif /* !defined lint */ |

| |

| /*LINTLIBRARY*/ |

| |

| #include "private.h" /* for time_t, TYPE_INTEGRAL, and TYPE_SIGNED */ |

| |

| double |

| difftime(time1, time0) |

| const time_t time1; |

| const time_t time0; |

| { |

| /* |

| ** If (sizeof (double) > sizeof (time_t)) simply convert and subtract |

| ** (assuming that the larger type has more precision). |

| ** This is the common real-world case circa 2004. |

| */ |

| if (sizeof (double) > sizeof (time_t)) |

| return (double) time1 - (double) time0; |

| if (!TYPE_INTEGRAL(time_t)) { |

| /* |

| ** time_t is floating. |

| */ |

| return time1 - time0; |

| } |

| if (!TYPE_SIGNED(time_t)) { |

| /* |

| ** time_t is integral and unsigned. |

| ** The difference of two unsigned values can't overflow |

| ** if the minuend is greater than or equal to the subtrahend. |

| */ |

| if (time1 >= time0) |

| return time1 - time0; |

| else return -((double) (time0 - time1)); |

| } |

| /* |

| ** time_t is integral and signed. |

| ** Handle cases where both time1 and time0 have the same sign |

| ** (meaning that their difference cannot overflow). |

| */ |

| if ((time1 < 0) == (time0 < 0)) |

| return time1 - time0; |

| /* |

| ** time1 and time0 have opposite signs. |

| ** Punt if unsigned long is too narrow. |

| */ |

| if (sizeof (unsigned long) < sizeof (time_t)) |

| return (double) time1 - (double) time0; |

| /* |

| ** Stay calm...decent optimizers will eliminate the complexity below. |

| */ |

| if (time1 >= 0 /* && time0 < 0 */) |

| return (unsigned long) time1 + |

| (unsigned long) (-(time0 + 1)) + 1; |

| return -(double) ((unsigned long) time0 + |

| (unsigned long) (-(time1 + 1)) + 1); |

| } |