1 /* 2 ** This file is in the public domain, so clarified as of 3 ** 1996-06-05 by Arthur David Olson. 4 */ 5 6 #ifndef lint 7 #ifndef NOID 8 static char elsieid[] = "@(#)difftime.c 8.1"; 9 #endif /* !defined NOID */ 10 #endif /* !defined lint */ 11 12 /*LINTLIBRARY*/ 13 14 #include "private.h" /* for time_t, TYPE_INTEGRAL, and TYPE_SIGNED */ 15 16 double 17 difftime(time1, time0) 18 const time_t time1; 19 const time_t time0; 20 { 21 /* 22 ** If (sizeof (double) > sizeof (time_t)) simply convert and subtract 23 ** (assuming that the larger type has more precision). 24 ** This is the common real-world case circa 2004. 25 */ 26 if (sizeof (double) > sizeof (time_t)) 27 return (double) time1 - (double) time0; 28 if (!TYPE_INTEGRAL(time_t)) { 29 /* 30 ** time_t is floating. 31 */ 32 return time1 - time0; 33 } 34 if (!TYPE_SIGNED(time_t)) { 35 /* 36 ** time_t is integral and unsigned. 37 ** The difference of two unsigned values can't overflow 38 ** if the minuend is greater than or equal to the subtrahend. 39 */ 40 if (time1 >= time0) 41 return time1 - time0; 42 else return -((double) (time0 - time1)); 43 } 44 /* 45 ** time_t is integral and signed. 46 ** Handle cases where both time1 and time0 have the same sign 47 ** (meaning that their difference cannot overflow). 48 */ 49 if ((time1 < 0) == (time0 < 0)) 50 return time1 - time0; 51 /* 52 ** time1 and time0 have opposite signs. 53 ** Punt if unsigned long is too narrow. 54 */ 55 if (sizeof (unsigned long) < sizeof (time_t)) 56 return (double) time1 - (double) time0; 57 /* 58 ** Stay calm...decent optimizers will eliminate the complexity below. 59 */ 60 if (time1 >= 0 /* && time0 < 0 */) 61 return (unsigned long) time1 + 62 (unsigned long) (-(time0 + 1)) + 1; 63 return -(double) ((unsigned long) time0 + 64 (unsigned long) (-(time1 + 1)) + 1); 65 } 66
