1 /* 2 ** This file is in the public domain, so clarified as of 3 ** 1996-06-05 by Arthur David Olson. 4 ** 5 ** $FreeBSD: src/lib/libc/stdtime/difftime.c,v 1.4.8.1 2001/03/05 11:37:21 obrien Exp $ 6 */ 7 /*LINTLIBRARY*/ 8 9 #include "namespace.h" 10 #include "private.h" 11 #include "un-namespace.h" 12 13 double 14 difftime(const time_t time1, const time_t time0) 15 { 16 /* 17 ** If (sizeof (double) > sizeof (time_t)) simply convert and subtract 18 ** (assuming that the larger type has more precision). 19 ** This is the common real-world case circa 2004. 20 */ 21 if (sizeof (double) > sizeof (time_t)) 22 return (double) time1 - (double) time0; 23 if (!TYPE_INTEGRAL(time_t)) { 24 /* 25 ** time_t is floating. 26 */ 27 return time1 - time0; 28 } 29 if (!TYPE_SIGNED(time_t)) { 30 /* 31 ** time_t is integral and unsigned. 32 ** The difference of two unsigned values can't overflow 33 ** if the minuend is greater than or equal to the subtrahend. 34 */ 35 if (time1 >= time0) 36 return time1 - time0; 37 else return -((double) (time0 - time1)); 38 } 39 /* 40 ** time_t is integral and signed. 41 ** Handle cases where both time1 and time0 have the same sign 42 ** (meaning that their difference cannot overflow). 43 */ 44 if ((time1 < 0) == (time0 < 0)) 45 return time1 - time0; 46 /* 47 ** time1 and time0 have opposite signs. 48 ** Punt if unsigned long is too narrow. 49 */ 50 if (sizeof (unsigned long) < sizeof (time_t)) 51 return (double) time1 - (double) time0; 52 /* 53 ** Stay calm...decent optimizers will eliminate the complexity below. 54 */ 55 if (time1 >= 0 /* && time0 < 0 */) 56 return (unsigned long) time1 + 57 (unsigned long) (-(time0 + 1)) + 1; 58 return -(double) ((unsigned long) time0 + 59 (unsigned long) (-(time1 + 1)) + 1); 60 } 61