1 /* $NetBSD: difftime.c,v 1.18 2017/10/24 17:38:17 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 1.18 2017/10/24 17:38:17 christos Exp $"); 14 #endif 15 #endif /* LIBC_SCCS and not lint */ 16 17 /*LINTLIBRARY*/ 18 19 #include "private.h" /* for time_t and TYPE_SIGNED */ 20 21 /* Return -X as a double. Using this avoids casting to 'double'. */ 22 static double 23 dminus(double x) 24 { 25 return -x; 26 } 27 28 double 29 difftime(time_t time1, time_t time0) 30 { 31 /* 32 ** If double is large enough, simply convert and subtract 33 ** (assuming that the larger type has more precision). 34 */ 35 /*CONSTCOND*/ 36 if (sizeof (time_t) < sizeof (double)) { 37 double t1 = time1, t0 = time0; 38 return t1 - t0; 39 } 40 41 /* 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 (!TYPE_SIGNED(time_t)) 46 return time0 <= time1 ? time1 - time0 : dminus(time0 - time1); 47 48 /* Use uintmax_t if wide enough. */ 49 /*CONSTCOND*/ 50 if (sizeof (time_t) <= sizeof (uintmax_t)) { 51 uintmax_t t1 = time1, t0 = time0; 52 return time0 <= time1 ? t1 - t0 : dminus(t0 - t1); 53 } 54 55 /* 56 ** Handle cases where both time1 and time0 have the same sign 57 ** (meaning that their difference cannot overflow). 58 */ 59 if ((time1 < 0) == (time0 < 0)) 60 return time1 - time0; 61 62 /* 63 ** The values have opposite signs and uintmax_t is too narrow. 64 ** This suffers from double rounding; attempt to lessen that 65 ** by using long double temporaries. 66 */ 67 { 68 long double t1 = time1, t0 = time0; 69 return t1 - t0; 70 } 71 } 72