/* error_demo1.c */

#include <stdio.h>
void add(float v, float *ans);

int main(int argc, char * argv[])
{
  float v[3];
  float ans = 0.0f;
  int i;

  printf("error_demo1.c 1.0e10f*((1.0f+1.0e-7f)-1.0f) \n");  
  printf("only about 7 digits accuracy, power of 10 not exact \n");
  v[0] = 1.0f; /* same as 1.0 double constant into float memory */
  v[1] = 1.0e-7f;
  v[2] = -1.0f;
  for(i=0; i<3; i++)
  {
    ans = ans + v[i]; /* should be kept in register */
  }
  ans = 1.0e10f * ans;
  printf("ans= %e \n", ans);

  printf("force store, break optimization, no difference here \n");
  ans = 0.0f;
  add(v[0], &ans);
  add(v[1], &ans);
  add(v[2], &ans);
  ans = 1.0e10f * ans;
  printf("ans= %e \n\n", ans);

  printf("expression with float  ans=%g \n", 1.0e10f*((1.0f+1.0e-7f)-1.0f));
  printf("expression with double ans=%g \n\n", 1.0e10*((1.0+1.0e-7)-1.0));

  printf("error_demo1.c (1.0f+0.5e-7f)+1.0f  too small \n");
  v[1] = 0.5e-7;
  ans = 0.0f;
  for(i=0; i<3; i++){
    ans = ans + v[i];
  }
  ans = 1.0e10f * ans;
  printf("ans= %e \n", ans);

  printf("force store, break optimization, no difference here \n");
  ans = 0.0f;
  add(v[0], &ans);
  add(v[1], &ans);
  add(v[2], &ans);
  ans = 1.0e10f * ans;
  printf("ans= %e \n", ans);
  return 0;
}

void add(float v, float *ans)
{
  *ans = *ans + v;
}