Exponential function benchmark in C

myexp.c

#include<stdio.h>
#include<math.h>

// thanks Joe from stackoverflow
#include <sys/time.h>
#include <sys/resource.h>

double get_time()
{
    struct timeval t;
    struct timezone tzp;
    gettimeofday(&t, &tzp);
    return t.tv_sec + t.tv_usec*1e-6;
}


//thanks Sun Microsystems and Naohiko Shimizu/Tokai University
double myexpm1(double x) {
  double ln2_hi = 6.93147180369123816490e-01;
  double ln2_lo = 1.90821492927058770002e-10;
  
  double one = 1.0;
  double Q[] = { 1.0,
		 -3.33333333333331316428e-02, 
		 1.58730158725481460165e-03, 
		 -7.93650757867487942473e-05,
		 4.00821782732936239552e-06, 
		 -2.01099218183624371326e-07};
  double hi = x - ln2_hi;
  double lo = ln2_lo;
  double k = 1;
  x = hi - lo;
  double c = (hi - x) - lo;
  double hfx = 0.5 * x;
  double hxs = x * hfx;
  double R1 = one + hxs * Q[1]; double h2 = hxs * hxs;
  double R2 = Q[2] + hxs * Q[3]; double h4 = h2 * h2;
  double R3 = Q[4] + hxs * Q[5];
  double r1 = R1 + h2 * R2 + h4 * R3;
  double t = 3.0 - r1 * hfx;
  double e = hxs * ((r1 - t) / (6.0 - x * t));
  e = (x * (e - c) - c);
  e -= hxs;
  return one + 2.0 * (x - e);
}

double myexp(double x) {
  double exm1 = myexpm1(x);
  return exm1 + 1;
}

double calcerr(double x) {
  double mye = myexp(x);
  double refe = exp(x);
  return mye - refe;
}

int main() {
  double nn[] = {1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e9};
  for (int n=0; n<7; n++) {
	double tic=get_time();
	double err=0;
	for(int i=0; i <= nn[n]; i++) {
	  double x = 0.4 + 0.6 * i/nn[n];
	  err = fmax(err, calcerr(x));
	}
	double toc = get_time();
	printf("(%g, %f, %g),\n", nn[n], toc-tic, err);
  }
}