/* ** This file is in the public domain, so clarified as of ** 1996-06-05 by Arthur David Olson. */ #include <sys/cdefs.h> #ifndef lint #ifndef NOID static char elsieid[] __unused = "@(#)difftime.c 8.1"; #endif /* !defined NOID */ #endif /* !defined lint */ __FBSDID("$FreeBSD: src/lib/libc/stdtime/difftime.c,v 1.9 2009/05/23 06:31:50 edwin Exp $"); /*LINTLIBRARY*/ #include "namespace.h" #include "private.h" /* for time_t, TYPE_INTEGRAL, and TYPE_SIGNED */ #include "un-namespace.h" 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); }