1 /* $NetBSD: difftime.c,v 1.11 2012/03/20 16:39:08 matt Exp $ */ 2 3 /* 4 ** This file is in the public domain, so clarified as of 5 ** 1996-06-05 by Arthur David Olson. 6 */ 7 8 #include <sys/cdefs.h> 9 #if defined(LIBC_SCCS) && !defined(lint) 10 #if 0 11 static char elsieid[] = "@(#)difftime.c 8.1"; 12 #else 13 __RCSID("$NetBSD: difftime.c,v 1.11 2012/03/20 16:39:08 matt Exp $"); 14 #endif 15 #endif /* LIBC_SCCS and not lint */ 16 17 /*LINTLIBRARY*/ 18 19 #include "private.h" /* for time_t, TYPE_INTEGRAL, and TYPE_SIGNED */ 20 21 double 22 difftime(const time_t time1, const time_t time0) 23 { 24 /* 25 ** If (sizeof (double) > sizeof (time_t)) simply convert and subtract 26 ** (assuming that the larger type has more precision). 27 ** This is the common real-world case circa 2004. 28 */ 29 /* LINTED constant */ 30 if (sizeof (double) > sizeof (time_t)) 31 return (double) time1 - (double) time0; 32 /* LINTED constant */ 33 if (!TYPE_INTEGRAL(time_t)) { 34 /* 35 ** time_t is floating. 36 */ 37 return time1 - time0; 38 } 39 /* LINTED constant */ 40 if (!TYPE_SIGNED(time_t)) { 41 /* 42 ** time_t is integral and unsigned. 43 ** The difference of two unsigned values can't overflow 44 ** if the minuend is greater than or equal to the subtrahend. 45 */ 46 if (time1 >= time0) 47 return time1 - time0; 48 else return -((double) (time0 - time1)); 49 } 50 /* 51 ** time_t is integral and signed. 52 ** Handle cases where both time1 and time0 have the same sign 53 ** (meaning that their difference cannot overflow). 54 */ 55 if ((time1 < 0) == (time0 < 0)) 56 return time1 - time0; 57 /* 58 ** time1 and time0 have opposite signs. 59 ** Punt if unsigned long is too narrow. 60 */ 61 /* CONSTCOND */ 62 if (sizeof (unsigned long) < sizeof (time_t)) 63 return (double) time1 - (double) time0; 64 /* 65 ** Stay calm...decent optimizers will eliminate the complexity below. 66 */ 67 if (time1 >= 0 /* && time0 < 0 */) 68 return (unsigned long) time1 + 69 (unsigned long) (-(time0 + 1)) + 1; 70 return -(double) ((unsigned long) time0 + 71 (unsigned long) (-(time1 + 1)) + 1); 72 } 73