1/* $NetBSD: difftime.c,v 1.24 2024/01/20 14:52:49 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 13static char elsieid[] = "@(#)difftime.c 8.1"; 14#else 15__RCSID("$NetBSD: difftime.c,v 1.24 2024/01/20 14:52:49 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'. */ 24static double 25dminus(double x) 26{ 27 return -x; 28} 29 30double 31difftime(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 /*NOTREACHED*/ 49 return time0 <= time1 ? time1 - time0 : 50 dminus((double)(time0 - time1)); 51 52 /* Use uintmax_t if wide enough. */ 53 /*CONSTCOND*/ 54 if (sizeof(time_t) <= sizeof(uintmax_t)) { 55 uintmax_t t1 = time1, t0 = time0; 56 return time0 <= time1 ? t1 - t0 : dminus((double)(t0 - t1)); 57 } 58 59 /* 60 ** Handle cases where both time1 and time0 have the same sign 61 ** (meaning that their difference cannot overflow). 62 */ 63 if ((time1 < 0) == (time0 < 0)) 64 return time1 - time0; 65 66 /* 67 ** The values have opposite signs and uintmax_t is too narrow. 68 ** This suffers from double rounding; attempt to lessen that 69 ** by using long double temporaries. 70 */ 71 { 72 long double t1 = time1, t0 = time0; 73 return t1 - t0; 74 } 75} 76