1/* Return the difference between two timestamps. */ 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/*LINTLIBRARY*/ 9 10#include "private.h" /* for time_t and TYPE_SIGNED */ 11 12/* Return -X as a double. Using this avoids casting to 'double'. */ 13static double 14dminus(double x) 15{ 16 return -x; 17} 18 19double 20difftime(time_t time1, time_t time0) 21{ 22 /* 23 ** If double is large enough, simply convert and subtract 24 ** (assuming that the larger type has more precision). 25 */ 26 if (sizeof(time_t) < sizeof(double)) { 27 double t1 = time1, t0 = time0; 28 return t1 - t0; 29 } 30 31 /* 32 ** The difference of two unsigned values can't overflow 33 ** if the minuend is greater than or equal to the subtrahend. 34 */ 35 if (!TYPE_SIGNED(time_t)) 36 return time0 <= time1 ? time1 - time0 : dminus(time0 - time1); 37 38 /* Use uintmax_t if wide enough. */ 39 if (sizeof(time_t) <= sizeof(uintmax_t)) { 40 uintmax_t t1 = time1, t0 = time0; 41 return time0 <= time1 ? t1 - t0 : dminus(t0 - t1); 42 } 43 44 /* 45 ** Handle cases where both time1 and time0 have the same sign 46 ** (meaning that their difference cannot overflow). 47 */ 48 if ((time1 < 0) == (time0 < 0)) 49 return time1 - time0; 50 51 /* 52 ** The values have opposite signs and uintmax_t is too narrow. 53 ** This suffers from double rounding; attempt to lessen that 54 ** by using long double temporaries. 55 */ 56 { 57 long double t1 = time1, t0 = time0; 58 return t1 - t0; 59 } 60} 61