Thread: Could this be done better ?

I was wondering if there was any one in here that could tell me if this code could be done better or faster. Take a look.

Code:

void VectorAngles( const float *forward, float *angles )
{
	float	tmp, yaw, pitch;
	
	if (forward[1] == 0 && forward[0] == 0)
	{
		yaw = 0;
		if (forward[2] > 0)
			pitch = 90.0;
		else
			pitch = 270.0;
	}
	else
	{
		yaw = (atan2f(forward[1], forward[0]) * 57.3f);
	
		
		if (yaw < 0) yaw += 360.0;

		tmp = sqrt (forward[0]*forward[0] + forward[1]*forward[1]);
		
		pitch = (atan2f(forward[2], tmp) * 57.3f);
		
		}

		angles[0] = pitch;
		angles[1] = yaw;
		angles[2] = 0;
}

This function works with pointers and changes array elements outside its scope. In big programs this is not desired. Perhaps you should use classes and references (C++ style).

Some people need faster sqrt-function than in <cmath>. Just try FastSQRT(...):

Code:

#include <iostream>
#include <conio.h>
#include <cmath>
#include <ctime> // clock_t, clock(), ...

using namespace std;

float FastSQRT( float r )
{
    // Null und negative Zahlen abfangen
    //if( r == 0.0f ) return 0.0f;
    if( r <  0.0f ) r = -r     ;
   
    // Startwert festlegen
    float val = r;
    float halfval = 0.5f * r;
    unsigned long *ptr = (unsigned long*)&r;
    *ptr = ( 0xbe6f0000 - *ptr ) >> 1;

    float temp = r;

    // Zwei Schritte reichen
    temp *= 1.5f - temp * temp * halfval;
    temp *= 1.5f - temp * temp * halfval;
    //temp *= 1.5f - temp * temp * halfval; //höhere Präzision   
   
    // Rückgabe
    return val*temp;
}

int main()
{
  double x;
  cout << "Bitte Zahl eingeben fuer Wurzelziehen: ";
  cin  >> x;
  cout << FastSQRT(x) << endl;
  cout << sqrt(x)     << endl << endl;
    
  // Zeitmessung
  const int NMAX = 20;
  int max;
  cout << "Anzahl Schleifendurchlaeufe? ";
  cin >> max;
  clock_t t1,t2;
  double ts, tm=0;

  double a;

  cout << endl;
  for(int n=0; n<NMAX; ++n)
  {
      t1 = clock(); // Start
      for( int i=0; i<max;i++) 
      {
        a = FastSQRT(x); //zu messende Aktion 1
      } 
      t2 = clock(); // Ende
      ts = (t2-t1)/static_cast<float>(CLOCKS_PER_SEC); // Zeit in Sekunden.
      cout << "Zeit Aktion 1: " << ts << " sec" << endl;
      tm += ts; // Das ist das Gleiche wie tm = tm + ts       
  }
  tm/=NMAX; // Das ist das Gleiche wie tm = tm / NMAX
  cout << "Durchschnitts-Zeit bei Aktion 1: " << tm << " sec" << endl;

  tm=0;
  cout << endl;
  for(int n=0; n<NMAX; ++n)
  {
      t1 = clock();
      for( int i=0; i<max;i++) 
      {
        a = sqrt(x); //zu messende Aktion 2
      } 
      t2 = clock();
      ts = (t2-t1)/static_cast<float>(CLOCKS_PER_SEC);
      cout << "Zeit bei Aktion 2: " << ts << " sec" << endl;
      tm += ts;    
  }
  tm/=NMAX;
  cout << "Durchschnitts-Zeit bei Aktion 2: " << tm << " sec" << endl;

  getch();
}

Thks for the reply's. according to my output running the code u posted erhard, the sqrt functions is faster.

I think modern compilers use special intructions for sqrt(), making such hacks worthless.

What about using valarray for the code above?If yes, could someone show me how to implement it.