1 /* $NetBSD: difftime.c,v 1.19 2018/10/19 23:05:35 christos Exp $ */ 2 3 /* Return the difference between two timestamps. */ 4 5 /* 6 ** This file is in the public domain, so clarified as of 7 ** 1996-06-05 by Arthur David Olson. 8 */ 9 10 #include <sys/cdefs.h> 11 #if defined(LIBC_SCCS) && !defined(lint) 12 #if 0 13 static char elsieid[] = "@(#)difftime.c 8.1"; 14 #else 15 __RCSID("$NetBSD: difftime.c,v 1.19 2018/10/19 23:05:35 christos Exp $"); 16 #endif 17 #endif /* LIBC_SCCS and not lint */ 18 19 /*LINTLIBRARY*/ 20 21 #include "private.h" /* for time_t and TYPE_SIGNED */ 22 23 /* Return -X as a double. Using this avoids casting to 'double'. */ 24 static double 25 dminus(double x) 26 { 27 return -x; 28 } 29 30 double 31 difftime(time_t time1, time_t time0) 32 { 33 /* 34 ** If double is large enough, simply convert and subtract 35 ** (assuming that the larger type has more precision). 36 */ 37 /*CONSTCOND*/ 38 if (sizeof (time_t) < sizeof (double)) { 39 double t1 = time1, t0 = time0; 40 return t1 - t0; 41 } 42 43 /* 44 ** The difference of two unsigned values can't overflow 45 ** if the minuend is greater than or equal to the subtrahend. 46 */ 47 if (!TYPE_SIGNED(time_t)) 48 return time0 <= time1 ? time1 - time0 : dminus(time0 - time1); 49 50 /* Use uintmax_t if wide enough. */ 51 /*CONSTCOND*/ 52 if (sizeof (time_t) <= sizeof (uintmax_t)) { 53 uintmax_t t1 = time1, t0 = time0; 54 return time0 <= time1 ? t1 - t0 : dminus(t0 - t1); 55 } 56 57 /* 58 ** Handle cases where both time1 and time0 have the same sign 59 ** (meaning that their difference cannot overflow). 60 */ 61 if ((time1 < 0) == (time0 < 0)) 62 return time1 - time0; 63 64 /* 65 ** The values have opposite signs and uintmax_t is too narrow. 66 ** This suffers from double rounding; attempt to lessen that 67 ** by using long double temporaries. 68 */ 69 { 70 long double t1 = time1, t0 = time0; 71 return t1 - t0; 72 } 73 } 74