1 /* $NetBSD: difftime.c,v 1.10 2009/12/31 22:49:16 mlelstv 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 1.10 2009/12/31 22:49:16 mlelstv 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(time1, time0) 23 const time_t time1; 24 const time_t time0; 25 { 26 /* 27 ** If (sizeof (double) > sizeof (time_t)) simply convert and subtract 28 ** (assuming that the larger type has more precision). 29 ** This is the common real-world case circa 2004. 30 */ 31 /* LINTED constant */ 32 if (sizeof (double) > sizeof (time_t)) 33 return (double) time1 - (double) time0; 34 /* LINTED constant */ 35 if (!TYPE_INTEGRAL(time_t)) { 36 /* 37 ** time_t is floating. 38 */ 39 return time1 - time0; 40 } 41 /* LINTED constant */ 42 if (!TYPE_SIGNED(time_t)) { 43 /* 44 ** time_t is integral and unsigned. 45 ** The difference of two unsigned values can't overflow 46 ** if the minuend is greater than or equal to the subtrahend. 47 */ 48 if (time1 >= time0) 49 return time1 - time0; 50 else return -((double) (time0 - time1)); 51 } 52 /* 53 ** time_t is integral and signed. 54 ** Handle cases where both time1 and time0 have the same sign 55 ** (meaning that their difference cannot overflow). 56 */ 57 if ((time1 < 0) == (time0 < 0)) 58 return time1 - time0; 59 /* 60 ** time1 and time0 have opposite signs. 61 ** Punt if unsigned long is too narrow. 62 */ 63 /* CONSTCOND */ 64 if (sizeof (unsigned long) < sizeof (time_t)) 65 return (double) time1 - (double) time0; 66 /* 67 ** Stay calm...decent optimizers will eliminate the complexity below. 68 */ 69 if (time1 >= 0 /* && time0 < 0 */) 70 return (unsigned long) time1 + 71 (unsigned long) (-(time0 + 1)) + 1; 72 return -(double) ((unsigned long) time0 + 73 (unsigned long) (-(time1 + 1)) + 1); 74 } 75