1 /* $NetBSD: difftime.c,v 1.14 2013/07/17 20:13:04 christos 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 1.14 2013/07/17 20:13:04 christos 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 ATTRIBUTE_CONST 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 */ 28 /*CONSTCOND*/ 29 if (sizeof (double) > sizeof (time_t)) 30 return (double) time1 - (double) time0; 31 /*LINTED const not */ 32 if (!TYPE_INTEGRAL(time_t)) { 33 /* 34 ** time_t is floating. 35 */ 36 return time1 - time0; 37 } 38 /*LINTED const not */ 39 if (!TYPE_SIGNED(time_t)) { 40 /* 41 ** time_t is integral and unsigned. 42 ** The difference of two unsigned values can't overflow 43 ** if the minuend is greater than or equal to the subtrahend. 44 */ 45 if (time1 >= time0) 46 return time1 - time0; 47 else return -(double) (time0 - time1); 48 } 49 /* 50 ** time_t is integral and signed. 51 ** Handle cases where both time1 and time0 have the same sign 52 ** (meaning that their difference cannot overflow). 53 */ 54 if ((time1 < 0) == (time0 < 0)) 55 return time1 - time0; 56 /* 57 ** time1 and time0 have opposite signs. 58 ** Punt if uintmax_t is too narrow. 59 ** This suffers from double rounding; attempt to lessen that 60 ** by using long double temporaries. 61 */ 62 /* CONSTCOND */ 63 if (sizeof (uintmax_t) < sizeof (time_t)) 64 return (double) time1 - (double) time0; 65 /* 66 ** Stay calm...decent optimizers will eliminate the complexity below. 67 */ 68 if (time1 >= 0 /* && time0 < 0 */) 69 return (uintmax_t) time1 + (uintmax_t) (-(time0 + 1)) + 1; 70 return -(double) ((uintmax_t) time0 + (uintmax_t) (-(time1 + 1)) + 1); 71 } 72