1#include <stdlib.h>
2#include <stdio.h>
3#include <unistd.h>
4#include <sys/limits.h>
5#include <sys/time.h>
6#include <time.h>
7#include <errno.h>
8
9#include <string.h>
10
11
12
13long long nanotime(void)
14{
15    struct timespec t;
16
17    if(clock_gettime(CLOCK_MONOTONIC, &t)) {
18        fprintf(stderr,"clock failure\n");
19        exit(1);
20    }
21
22    return (((long long) t.tv_sec) * 1000000000LL) +
23        ((long long) t.tv_nsec);
24}
25
26static struct timespec ts_sub(struct timespec a, struct timespec b)
27{
28    struct timespec r;
29    r.tv_sec = a.tv_sec - b.tv_sec;
30    r.tv_nsec = a.tv_nsec - b.tv_nsec;
31    if(r.tv_nsec < 0) {
32        r.tv_sec--;
33        r.tv_nsec += 1000 * 1000 * 1000;
34    }
35    if(r.tv_sec < 0 && r.tv_nsec > 0) {
36        r.tv_sec++;
37        r.tv_nsec -= 1000 * 1000 * 1000;
38    }
39    return r;
40}
41
42static struct timespec ts_min(struct timespec a, struct timespec b)
43{
44    if(a.tv_sec < b.tv_sec || (a.tv_sec == b.tv_sec && a.tv_nsec < b.tv_nsec))
45        return a;
46    else
47        return b;
48}
49
50static struct timespec ts_max(struct timespec a, struct timespec b)
51{
52    if(a.tv_sec < b.tv_sec || (a.tv_sec == b.tv_sec && a.tv_nsec < b.tv_nsec))
53        return b;
54    else
55        return a;
56}
57
58int main(int argc, char **argv)
59{
60    long long tnow, tlast;
61    struct timespec t1, dtmin, dtminp, dtmax;
62    int print_interval = 50000;
63    int print_countdown = 1;
64    int clock_id = CLOCK_MONOTONIC;
65    dtmin.tv_sec = INT_MAX;
66    dtmin.tv_nsec = 0;
67    dtminp.tv_sec = INT_MAX;
68    dtminp.tv_nsec = 0;
69    dtmax.tv_sec = 0;
70    dtmax.tv_nsec = 0;
71    tlast = 0;
72
73    if(argc == 2) {
74        clock_id = atoi(argv[1]);
75        printf("using clock %d\n", clock_id);
76    }
77    clock_gettime(clock_id, &t1);
78
79    for(;;) {
80        struct timespec t, dt;
81        clock_gettime(clock_id, &t);
82        dt = ts_sub(t, t1);
83        t1 = t;
84        dtmin = ts_min(dtmin, dt);
85        if(dt.tv_sec > 0 || dt.tv_nsec > 0)
86            dtminp = ts_min(dtminp, dt);
87        if(print_countdown != print_interval)
88            dtmax = ts_max(dtmax, dt);
89        if(--print_countdown == 0) {
90            fprintf(stderr,"%09ld.%09ld, dt %ld.%09ld, min %ld.%09ld, minp %ld.%09ld, max %ld.%09ld\n",
91                    t.tv_sec, t.tv_nsec, dt.tv_sec, dt.tv_nsec,
92                    dtmin.tv_sec, dtmin.tv_nsec, dtminp.tv_sec, dtminp.tv_nsec,
93                    dtmax.tv_sec, dtmax.tv_nsec);
94            print_countdown = print_interval;
95        }
96    }
97    for(;;) {
98        tnow = nanotime();
99        if(tnow < tlast) {
100#if 0
101            fprintf(stderr,"time went backwards: %lld -> %lld\n",
102                    tlast, tnow);
103            exit(1);
104#endif
105            fprintf(stderr,"%lld ROLLBACK\n", tnow);
106        } else {
107            fprintf(stderr,"%lld\n", tnow);
108        }
109        tlast = tnow;
110    }
111
112    return 0;
113}
114