/* 
 * Program to measure high-res timer latency.
 *
 */
#include <stdint.h>
#include <stdbool.h>
#include <sys/types.h>
#include <unistd.h>
#include <time.h>
#include <errno.h>
#include <string.h>
#include <stdio.h>

#ifndef N_SAMPLES
#define N_SAMPLES 100
#endif


int main(int argc, char *const* argv, char *const* envp)
{ clockid_t clk = CLOCK_MONOTONIC_RAW;
  if((argc > 1) && (argv[1] != NULL) && (0 == strcmp(argv[1],"-m")))
    clk = CLOCK_MONOTONIC;  
  struct timespec sample[N_SAMPLES+1];
  unsigned int cnt=N_SAMPLES, s=0 ;
  do
  { if( 0 != clock_gettime(CLOCK_MONOTONIC_RAW, &sample[s++]) )
    { fprintf(stderr,"oops, clock_gettime() failed: %d: '%s'.\n", errno, strerror(errno));
      return 1;
    }
  }while( --cnt );
  clock_gettime(CLOCK_MONOTONIC_RAW, &sample[s]);
#define TS2NS(_TS_) ((((unsigned long long)(_TS_).tv_sec)*1000000000ULL) + (((unsigned long long)((_TS_).tv_nsec)))) 
  unsigned long long
    deltas [ N_SAMPLES ]
  , t1, t2, sum=0
  , t_start = TS2NS(sample[0]);
  for(s=1; s < (N_SAMPLES+1); s+=1)
  { t1 = TS2NS(sample[s-1]);
    t2 = TS2NS(sample[s]);
    deltas[s-1]=t2-t1;
  }  
  for(s = 0; s < N_SAMPLES; s+=1)
    sum += deltas[s];
  fprintf(stderr,"sum: %llu\n",sum);
  unsigned long long avg_ns = sum / N_SAMPLES;
  t1=(t2 - t_start);
  fprintf(stderr,
	  "Total time: %1.1llu.%9.9lluS - Average Latency: %1.1llu.%9.9lluS\n",
          t1/1000000000,       t1-((t1/1000000000)*1000000000),
          avg_ns/1000000000,   avg_ns-((avg_ns/1000000000)*1000000000)   
	  );	  
  return 0;
}