117209Swollman/* 217209Swollman** This file is in the public domain, so clarified as of 3192625Sedwin** 1996-06-05 by Arthur David Olson. 417209Swollman*/ 515923Sscrappy 6111010Snectar#include <sys/cdefs.h> 72708Swollman#ifndef lint 82708Swollman#ifndef NOID 9192625Sedwinstatic char elsieid[] __unused = "@(#)difftime.c 8.1"; 102708Swollman#endif /* !defined NOID */ 112708Swollman#endif /* !defined lint */ 1292986Sobrien__FBSDID("$FreeBSD$"); 132708Swollman 142708Swollman/*LINTLIBRARY*/ 152708Swollman 1671579Sdeischen#include "namespace.h" 17192625Sedwin#include "private.h" /* for time_t, TYPE_INTEGRAL, and TYPE_SIGNED */ 1871579Sdeischen#include "un-namespace.h" 192708Swollman 202708Swollmandouble 212708Swollmandifftime(time1, time0) 222708Swollmanconst time_t time1; 232708Swollmanconst time_t time0; 242708Swollman{ 25192625Sedwin /* 26192625Sedwin ** If (sizeof (double) > sizeof (time_t)) simply convert and subtract 27192625Sedwin ** (assuming that the larger type has more precision). 28192625Sedwin ** This is the common real-world case circa 2004. 29192625Sedwin */ 30192625Sedwin if (sizeof (double) > sizeof (time_t)) 31192625Sedwin return (double) time1 - (double) time0; 32192625Sedwin if (!TYPE_INTEGRAL(time_t)) { 33192625Sedwin /* 34192625Sedwin ** time_t is floating. 35192625Sedwin */ 36192625Sedwin return time1 - time0; 37130461Sstefanf } 38192625Sedwin if (!TYPE_SIGNED(time_t)) { 39192625Sedwin /* 40192625Sedwin ** time_t is integral and unsigned. 41192625Sedwin ** The difference of two unsigned values can't overflow 42192625Sedwin ** if the minuend is greater than or equal to the subtrahend. 43192625Sedwin */ 44192625Sedwin if (time1 >= time0) 45192625Sedwin return time1 - time0; 46192625Sedwin else return -((double) (time0 - time1)); 47192625Sedwin } 482708Swollman /* 49192625Sedwin ** time_t is integral and signed. 50192625Sedwin ** Handle cases where both time1 and time0 have the same sign 51192625Sedwin ** (meaning that their difference cannot overflow). 522708Swollman */ 53192625Sedwin if ((time1 < 0) == (time0 < 0)) 54192625Sedwin return time1 - time0; 552708Swollman /* 56192625Sedwin ** time1 and time0 have opposite signs. 57192625Sedwin ** Punt if unsigned long is too narrow. 582708Swollman */ 59192625Sedwin if (sizeof (unsigned long) < sizeof (time_t)) 60192625Sedwin return (double) time1 - (double) time0; 612708Swollman /* 62192625Sedwin ** Stay calm...decent optimizers will eliminate the complexity below. 632708Swollman */ 64192625Sedwin if (time1 >= 0 /* && time0 < 0 */) 65192625Sedwin return (unsigned long) time1 + 66192625Sedwin (unsigned long) (-(time0 + 1)) + 1; 67192625Sedwin return -(double) ((unsigned long) time0 + 68192625Sedwin (unsigned long) (-(time1 + 1)) + 1); 692708Swollman} 70