1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
|
/* Copyright (C) 1991-2022 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <time.h>
#include <limits.h>
#include <float.h>
#include <stdint.h>
#define TYPE_BITS(type) (sizeof (type) * CHAR_BIT)
#define TYPE_FLOATING(type) ((type) 0.5 == 0.5)
#define TYPE_SIGNED(type) ((type) -1 < 0)
/* Return the difference between TIME1 and TIME0, where TIME0 <= TIME1.
time_t is known to be an integer type. */
static double
subtract (__time64_t time1, __time64_t time0)
{
if (! TYPE_SIGNED (__time64_t))
return time1 - time0;
else
{
/* Optimize the common special cases where time_t
can be converted to uintmax_t without losing information. */
uintmax_t dt = (uintmax_t) time1 - (uintmax_t) time0;
double delta = dt;
if (UINTMAX_MAX / 2 < INTMAX_MAX)
{
/* This is a rare host where uintmax_t has padding bits, and possibly
information was lost when converting time_t to uintmax_t.
Check for overflow by comparing dt/2 to (time1/2 - time0/2).
Overflow occurred if they differ by more than a small slop.
Thanks to Clive D.W. Feather for detailed technical advice about
hosts with padding bits.
In the following code the "h" prefix means half. By range
analysis, we have:
-0.5 <= ht1 - 0.5*time1 <= 0.5
-0.5 <= ht0 - 0.5*time0 <= 0.5
-1.0 <= dht - 0.5*(time1 - time0) <= 1.0
If overflow has not occurred, we also have:
-0.5 <= hdt - 0.5*(time1 - time0) <= 0
-1.0 <= dht - hdt <= 1.5
and since dht - hdt is an integer, we also have:
-1 <= dht - hdt <= 1
or equivalently:
0 <= dht - hdt + 1 <= 2
In the above analysis, all the operators have their exact
mathematical semantics, not C semantics. However, dht - hdt +
1 is unsigned in C, so it need not be compared to zero. */
uintmax_t hdt = dt / 2;
__time64_t ht1 = time1 / 2;
__time64_t ht0 = time0 / 2;
__time64_t dht = ht1 - ht0;
if (2 < dht - hdt + 1)
{
/* Repair delta overflow.
The following expression contains a second rounding,
so the result may not be the closest to the true answer.
This problem occurs only with very large differences.
It's too painful to fix this portably. */
delta = dt + 2.0L * (UINTMAX_MAX - UINTMAX_MAX / 2);
}
}
return delta;
}
}
/* Return the difference between TIME1 and TIME0. */
double
__difftime64 (__time64_t time1, __time64_t time0)
{
/* Convert to double and then subtract if no double-rounding error could
result. */
if (TYPE_BITS (__time64_t) <= DBL_MANT_DIG
|| (TYPE_FLOATING (__time64_t) && sizeof (__time64_t) < sizeof (long double)))
return (double) time1 - (double) time0;
/* Likewise for long double. */
if (TYPE_BITS (__time64_t) <= LDBL_MANT_DIG || TYPE_FLOATING (__time64_t))
return (long double) time1 - (long double) time0;
/* Subtract the smaller integer from the larger, convert the difference to
double, and then negate if needed. */
return time1 < time0 ? - subtract (time0, time1) : subtract (time1, time0);
}
/* Provide a 32-bit wrapper if needed. */
#if __TIMESIZE != 64
libc_hidden_def (__difftime64)
double
__difftime (time_t time1, time_t time0)
{
return __difftime64 (time1, time0);
}
#endif
strong_alias (__difftime, difftime)
|
