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 21 difftime(time1, time0) 22 const time_t time1; 23 const time_t time0; 24 { 25 /* 26 ** If (sizeof (double) > sizeof (time_t)) simply convert and subtract 27 ** (assuming that the larger type has more precision). 28 ** This is the common real-world case circa 2004. 29 */ 30 if (sizeof (double) > sizeof (time_t)) 31 return (double) time1 - (double) time0; 32 if (!TYPE_INTEGRAL(time_t)) { 33 /* 34 ** time_t is floating. 35 */ 36 return time1 - time0; 37 } 38 if (!TYPE_SIGNED(time_t)) { 39 /* 40 ** time_t is integral and unsigned. 41 ** The difference of two unsigned values can't overflow 42 ** if the minuend is greater than or equal to the subtrahend. 43 */ 44 if (time1 >= time0) 45 return time1 - time0; 46 else return -((double) (time0 - time1)); 47 } 48 /* 49 ** time_t is integral and signed. 50 ** Handle cases where both time1 and time0 have the same sign 51 ** (meaning that their difference cannot overflow). 52 */ 53 if ((time1 < 0) == (time0 < 0)) 54 return time1 - time0; 55 /* 56 ** time1 and time0 have opposite signs. 57 ** Punt if unsigned long is too narrow. 58 */ 59 if (sizeof (unsigned long) < sizeof (time_t)) 60 return (double) time1 - (double) time0; 61 /* 62 ** Stay calm...decent optimizers will eliminate the complexity below. 63 */ 64 if (time1 >= 0 /* && time0 < 0 */) 65 return (unsigned long) time1 + 66 (unsigned long) (-(time0 + 1)) + 1; 67 return -(double) ((unsigned long) time0 + 68 (unsigned long) (-(time1 + 1)) + 1); 69 } 70