1 /* 2 ** This file is in the public domain, so clarified as of 3 ** 1996-06-05 by Arthur David Olson. 4 */ 5 6 #include <sys/cdefs.h> 7 #ifndef lint 8 #ifndef NOID 9 static char elsieid[] __unused = "@(#)difftime.c 8.1"; 10 #endif /* !defined NOID */ 11 #endif /* !defined lint */ 12 __FBSDID("$FreeBSD$"); 13 14 /*LINTLIBRARY*/ 15 16 #include "namespace.h" 17 #include "private.h" /* for time_t, TYPE_INTEGRAL, and TYPE_SIGNED */ 18 #include "un-namespace.h" 19 20 double difftime(const time_t time1,const time_t time0)21difftime(const time_t time1, const time_t time0) 22 { 23 /* 24 ** If (sizeof (double) > sizeof (time_t)) simply convert and subtract 25 ** (assuming that the larger type has more precision). 26 ** This is the common real-world case circa 2004. 27 */ 28 if (sizeof (double) > sizeof (time_t)) 29 return (double) time1 - (double) time0; 30 if (!TYPE_INTEGRAL(time_t)) { 31 /* 32 ** time_t is floating. 33 */ 34 return time1 - time0; 35 } 36 if (!TYPE_SIGNED(time_t)) { 37 /* 38 ** time_t is integral and unsigned. 39 ** The difference of two unsigned values can't overflow 40 ** if the minuend is greater than or equal to the subtrahend. 41 */ 42 if (time1 >= time0) 43 return time1 - time0; 44 else return -((double) (time0 - time1)); 45 } 46 /* 47 ** time_t is integral and signed. 48 ** Handle cases where both time1 and time0 have the same sign 49 ** (meaning that their difference cannot overflow). 50 */ 51 if ((time1 < 0) == (time0 < 0)) 52 return time1 - time0; 53 /* 54 ** time1 and time0 have opposite signs. 55 ** Punt if unsigned long is too narrow. 56 */ 57 if (sizeof (unsigned long) < sizeof (time_t)) 58 return (double) time1 - (double) time0; 59 /* 60 ** Stay calm...decent optimizers will eliminate the complexity below. 61 */ 62 if (time1 >= 0 /* && time0 < 0 */) 63 return (unsigned long) time1 + 64 (unsigned long) (-(time0 + 1)) + 1; 65 return -(double) ((unsigned long) time0 + 66 (unsigned long) (-(time1 + 1)) + 1); 67 } 68