1 /* 2 ** This file is in the public domain, so clarified as of 3 ** 1996-06-05 by Arthur David Olson. 4 ** 5 ** $FreeBSD: head/contrib/tzcode/stdtime/difftime.c 192625 2009-05-23 06:31:50Z edwin $ 6 */ 7 /*LINTLIBRARY*/ 8 9 #include "namespace.h" 10 #include "private.h" /* for time_t and TYPE_SIGNED */ 11 #include "un-namespace.h" 12 13 double 14 difftime(time_t time1, time_t time0) 15 { 16 /* 17 ** If (sizeof (double) > sizeof (time_t)) simply convert and subtract 18 ** (assuming that the larger type has more precision). 19 */ 20 if (sizeof (double) > sizeof (time_t)) 21 return (double) time1 - (double) time0; 22 if (!TYPE_SIGNED(time_t)) { 23 /* 24 ** The difference of two unsigned values can't overflow 25 ** if the minuend is greater than or equal to the subtrahend. 26 */ 27 if (time1 >= time0) 28 return time1 - time0; 29 else return -(double) (time0 - time1); 30 } 31 /* 32 ** Handle cases where both time1 and time0 have the same sign 33 ** (meaning that their difference cannot overflow). 34 */ 35 if ((time1 < 0) == (time0 < 0)) 36 return time1 - time0; 37 /* 38 ** time1 and time0 have opposite signs. 39 ** Punt if uintmax_t is too narrow. 40 ** This suffers from double rounding; attempt to lessen that 41 ** by using long double temporaries. 42 */ 43 if (sizeof (uintmax_t) < sizeof (time_t)) 44 return (long double) time1 - (long double) time0; 45 /* 46 ** Stay calm...decent optimizers will eliminate the complexity below. 47 */ 48 if (time1 >= 0 /* && time0 < 0 */) 49 return (uintmax_t) time1 + (uintmax_t) (-1 - time0) + 1; 50 return -(double) ((uintmax_t) time0 + (uintmax_t) (-1 - time1) + 1); 51 } 52