| 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 */ |
| 12 | double my_difftime(time_t left, time_t right) { |
| 13 | double diff = (double)left - (double)right; |
| 14 | return diff; |
| 15 | } |
| 16 | |
| 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 | |
| 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 | |
| 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 | } |