//----------------------------------------------------------------------------

#ifndef PERFORMANCES_H
#define PERFORMANCES_H

double
sum(const double *values,
    int valueCount);

int
halfValues(const double *values,
           int valueCount);

double
mean(const double *values,
     int valueCount);

double
variance(const double *values,
         int valueCount);

#endif // PERFORMANCES_H

//----------------------------------------------------------------------------

//----------------------------------------------------------------------------

#include "performances.h"

#include <assert.h>

#define INITIAL_VERSION 0

double
sum(const double *values,
    int valueCount)
{
  double sum=0.0;
  for(int i=0; i<valueCount; ++i)
  {
    sum+=values[i];
  }
  return sum;
}

int
halfValues(const double *values,
           int valueCount)
{
  assert(valueCount>0); // detect incorrect parameter
  int split=-1;
  double partialSum=0.0;
#if INITIAL_VERSION
  for(int i=0; i<valueCount; ++i)
  {
    partialSum+=values[i];
    if(partialSum>0.5*sum(values, valueCount))
    {
      break;
    }
    split=i;
  }
#else // prevent multiple useless evaluations
  const double halfTotalSum=0.5*sum(values, valueCount);
  for(int i=0; i<valueCount; ++i)
  {
    partialSum+=values[i];
    if(partialSum>halfTotalSum)
    {
      break;
    }
    split=i;
  }
#endif
  return split;
}

double
mean(const double *values,
     int valueCount)
{
  double sum=0.0;
  for(int i=0; i<valueCount; ++i)
  {
    sum+=values[i];
  }
  return sum/valueCount;
}

double
variance(const double *values,
         int valueCount)
{
  assert(valueCount>0); // detect incorrect parameter
  double sqrSum=0.0;
#if INITIAL_VERSION
  for(int i=0; i<valueCount; ++i)
  {
    const double delta=values[i]-mean(values, valueCount);
    sqrSum+=delta*delta;
  }
#else // prevent multiple useless evaluations
  const double meanValue=mean(values, valueCount);
  for(int i=0; i<valueCount; ++i)
  {
    const double delta=values[i]-meanValue;
    sqrSum+=delta*delta;
  }
#endif
  return sqrSum/valueCount;
}

//----------------------------------------------------------------------------

//----------------------------------------------------------------------------

#include "performances.h"

#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>

#define INTENTIONAL_BUG 0

double // seconds (1e-6 precision) since 1970/01/01 00:00:00 UTC
now(void)
{
  struct timeval tv;
  gettimeofday(&tv, NULL);
  return (double)tv.tv_sec+1e-6*(double)tv.tv_usec;
}

void
test_halfValues(void)
{
  printf("\n~~~~ %s() ~~~~\n", __func__);
  const int valueCount=10000;
  double *values=(double *)malloc(valueCount*sizeof(double));
  if(values==NULL)
  {
    abort();
  }
  for(int i=0; i<valueCount; ++i)
  {
    const double value=i*0.01;
    values[i]=value*value;
  }
  const double t0=now();
  double duration=0.0;
  int result, iterCount;
  for(iterCount=0; duration<5.0; ++iterCount, duration=now()-t0)
  {
#if INTENTIONAL_BUG
    // artificially generate an assertion failure
    // in order to illustrate assert()
    result=halfValues(values, 0);
#else // normal computation
    result=halfValues(values, valueCount);
#endif
  }
  printf("result=%d --> %g it/s\n", result, iterCount/duration);
  free(values);
}

void
test_variance(void)
{
  printf("\n~~~~ %s() ~~~~\n", __func__);
  const int valueCount=10000;
  double *values=(double *)malloc(valueCount*sizeof(double));
  if(values==NULL)
  {
    abort();
  }
  for(int i=0; i<valueCount; ++i)
  {
    const double value=(i%1000)*0.01;
    values[i]=value*value;
  }
  const double t0=now();
  double result, duration=0.0;
  int iterCount;
  for(iterCount=0; duration<5.0; ++iterCount, duration=now()-t0)
  {
#if INTENTIONAL_BUG
    // artificially generate an assertion failure
    // in order to illustrate assert()
    result=variance(values, 0);
#else // normal computation
    result=variance(values, valueCount);
#endif
  }
  printf("result=%g --> %g it/s\n", result, iterCount/duration);
  free(values);
}

int
main(void)
{
  test_halfValues();
  test_variance();
  return 0;
}

//----------------------------------------------------------------------------