pow(x,4) approximation

References : Posted by Stefan Stenzel
Notes :
Very hacked, but it gives a rough estimate of x**4 by modifying exponent and mantissa.
Code :
float p4fast(float in)
{
  long *lp,l;

  lp=(long *)(&in);
  l=*lp;

  l-=0x3F800000l; /* un-bias */
  l<<=2;          /* **4 */
  l+=0x3F800000l; /* bias */
  *lp=l;

  /* compiler will read this from memory since & operator had been used */
  return in;
}