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 "namespace.h"
11#include "private.h"	/* for time_t and TYPE_SIGNED */
12#include "un-namespace.h"
13
14/* Return -X as a double.  Using this avoids casting to 'double'.  */
15static double
16dminus(double x)
17{
18  return -x;
19}
20
21double
22difftime(time_t time1, time_t time0)
23{
24	/*
25	** If double is large enough, simply convert and subtract
26	** (assuming that the larger type has more precision).
27	*/
28	if (sizeof(time_t) < sizeof(double)) {
29	  double t1 = time1, t0 = time0;
30	  return t1 - t0;
31	}
32
33	/*
34	** The difference of two unsigned values can't overflow
35	** if the minuend is greater than or equal to the subtrahend.
36	*/
37	if (!TYPE_SIGNED(time_t))
38	  return time0 <= time1 ? time1 - time0 : dminus(time0 - time1);
39
40	/* Use uintmax_t if wide enough.  */
41	if (sizeof(time_t) <= sizeof(uintmax_t)) {
42	  uintmax_t t1 = time1, t0 = time0;
43	  return time0 <= time1 ? t1 - t0 : dminus(t0 - t1);
44	}
45
46	/*
47	** Handle cases where both time1 and time0 have the same sign
48	** (meaning that their difference cannot overflow).
49	*/
50	if ((time1 < 0) == (time0 < 0))
51	  return time1 - time0;
52
53	/*
54	** The values have opposite signs and uintmax_t is too narrow.
55	** This suffers from double rounding; attempt to lessen that
56	** by using long double temporaries.
57	*/
58	{
59	  long double t1 = time1, t0 = time0;
60	  return t1 - t0;
61	}
62}
63