time.c

#define _POSIX_C_SOURCE 199309L

#include <stdlib.h>
#include <stdio.h>
#include <stdbool.h>
#include <stdint.h>
#include <time.h>
#include <signal.h>

#define GTCHECK(EXP) \
  do { \
    int e = EXP; \
    if (0 != e) { \
      fprintf(stderr, "ERROR: clock_gettime failed (%d). %s:%d\n", e, __FILE__, __LINE__); \
      exit(e); \
    } \
  } while(0)
      

#define GT(PTR) clock_gettime(CLOCK_BOOTTIME, (PTR))

void done(int param);

static struct timespec t;
static uint64_t ts[128] = { 0 };

static uint64_t t_to_u64(struct timespec * t) {
  return (t->tv_sec * 1000000000) + t->tv_nsec;
}

int main(int argc, char * argv[]) {
  (void)argc;
  (void)argv;

  signal(SIGINT, done);

  /* Setup the first sample. */
  GTCHECK(GT(&t));
  uint64_t first = t_to_u64(&t);

  GTCHECK(GT(&t));
  uint64_t second = t_to_u64(&t);

  ts[0] = second - first;

  uint64_t last = second;

  /* Begin sampling the clock as fast as possible. */
  for (int i = 1; i < sizeof(ts)/sizeof(ts[0]); i++) {
    while(true) {
      GTCHECK(GT(&t));

      uint64_t v = t_to_u64(&t);
      uint64_t diff = v - last;
      last = v;

      if (diff > ts[i - 1]) {
        ts[i] = diff;
        break;
      }
    }
  }

  done(0);

  return 0;
}

void done(int param) {
  (void)param;
  printf("Done!\n"); 

  for (int i = 0; i < sizeof(ts)/sizeof(ts[0]) && ts[i]; i++) {
    fprintf(stdout, "diff=%lu\n", ts[i]);
  }

  exit(0);
}