1 /* 2 ** This file is in the public domain, so clarified as of 3 ** 1996-06-05 by Arthur David Olson. 4 ** 5 ** @(#)difftime.c 7.7 6 ** $FreeBSD: src/lib/libc/stdtime/difftime.c,v 1.4.8.1 2001/03/05 11:37:21 obrien Exp $ 7 ** $DragonFly: src/lib/libc/stdtime/difftime.c,v 1.5 2008/10/19 20:15:58 swildner Exp $ 8 */ 9 /*LINTLIBRARY*/ 10 11 #include "namespace.h" 12 #include "private.h" 13 #include "un-namespace.h" 14 15 double 16 difftime(const time_t time1, const time_t time0) 17 { 18 /* 19 ** If (sizeof (double) > sizeof (time_t)) simply convert and subtract 20 ** (assuming that the larger type has more precision). 21 ** This is the common real-world case circa 2004. 22 */ 23 if (sizeof (double) > sizeof (time_t)) 24 return (double) time1 - (double) time0; 25 if (!TYPE_INTEGRAL(time_t)) { 26 /* 27 ** time_t is floating. 28 */ 29 return time1 - time0; 30 } 31 if (!TYPE_SIGNED(time_t)) { 32 /* 33 ** time_t is integral and unsigned. 34 ** The difference of two unsigned values can't overflow 35 ** if the minuend is greater than or equal to the subtrahend. 36 */ 37 if (time1 >= time0) 38 return time1 - time0; 39 else return -((double) (time0 - time1)); 40 } 41 /* 42 ** time_t is integral and signed. 43 ** Handle cases where both time1 and time0 have the same sign 44 ** (meaning that their difference cannot overflow). 45 */ 46 if ((time1 < 0) == (time0 < 0)) 47 return time1 - time0; 48 /* 49 ** time1 and time0 have opposite signs. 50 ** Punt if unsigned long is too narrow. 51 */ 52 if (sizeof (unsigned long) < sizeof (time_t)) 53 return (double) time1 - (double) time0; 54 /* 55 ** Stay calm...decent optimizers will eliminate the complexity below. 56 */ 57 if (time1 >= 0 /* && time0 < 0 */) 58 return (unsigned long) time1 + 59 (unsigned long) (-(time0 + 1)) + 1; 60 return -(double) ((unsigned long) time0 + 61 (unsigned long) (-(time1 + 1)) + 1); 62 } 63