1 /* A little program to test the limits of your system's time functions
2 * See Porting/README.y2038 for details
3 */
4
5 #include <time.h>
6 #include <stdio.h>
7 #include <math.h>
8
9 time_t Time_Zero = 0;
10
11 /* Visual C++ 2008's difftime() can't do negative times */
my_difftime(time_t left,time_t right)12 double my_difftime(time_t left, time_t right) {
13 double diff = (double)left - (double)right;
14 return diff;
15 }
16
check_date_max(struct tm * (* date_func)(const time_t *),char * func_name)17 void check_date_max( struct tm * (*date_func)(const time_t *), char *func_name ) {
18 struct tm *date;
19 time_t time = 0;
20 time_t last_time = 0;
21 time_t time_change;
22 int i;
23
24 for (i = 0; i <= 63; i++) {
25 date = (*date_func)(&time);
26
27 /* date_func() broke or tm_year overflowed */
28 if(date == NULL || date->tm_year < 69)
29 break;
30
31 last_time = time;
32 time += time + 1;
33
34 /* time_t overflowed */
35 if( time < last_time )
36 break;
37 }
38
39 /* Binary search for the exact failure point */
40 time = last_time;
41 time_change = last_time / 2;
42
43 do {
44 time += time_change;
45
46 date = (*date_func)(&time);
47
48 /* date_func() broke or tm_year overflowed or time_t overflowed */
49 if(date == NULL || date->tm_year < 69 || time < last_time) {
50 time = last_time;
51 time_change = time_change / 2;
52 }
53 else {
54 last_time = time;
55 }
56 } while(time_change > 0);
57
58 printf("%20s max %.0f\n", func_name, my_difftime(last_time, Time_Zero));
59 }
60
61
check_date_min(struct tm * (* date_func)(const time_t *),char * func_name)62 void check_date_min( struct tm * (*date_func)(const time_t *), char *func_name ) {
63 struct tm *date;
64 time_t time = -1;
65 time_t last_time = 0;
66 time_t time_change;
67 int i;
68
69 for (i = 1; i <= 63; i++) {
70 date = (*date_func)(&time);
71
72 /* date_func() broke or tm_year underflowed */
73 if(date == NULL || date->tm_year > 70)
74 break;
75
76 last_time = time;
77 time += time;
78
79 /* time_t underflowed */
80 if( time > last_time )
81 break;
82 }
83
84 /* Binary search for the exact failure point */
85 time = last_time;
86 time_change = last_time / 2;
87
88 do {
89 time += time_change;
90
91 date = (*date_func)(&time);
92
93 /* gmtime() broke or tm_year overflowed or time_t overflowed */
94 if(date == NULL || date->tm_year > 70 || time > last_time) {
95 time = last_time;
96 time_change = time_change / 2;
97 }
98 else {
99 last_time = time;
100 }
101 } while(time_change < 0);
102
103 printf("%20s min %.0f\n", func_name, my_difftime(last_time, Time_Zero));
104 }
105
106
main(void)107 int main(void) {
108 check_date_max(gmtime, "gmtime");
109 check_date_max(localtime, "localtime");
110 check_date_min(gmtime, "gmtime");
111 check_date_min(localtime, "localtime");
112
113 return 0;
114 }
115