Hey 54.226.34.209, do you really want to belong to yesterday's generation? Nag your ISP about the all-new and shiny IPv6
bikesandcode — + 12 - — Oct. 17, 2010, 11:56 a.m.

Taken from the Quake III source, I stumbled across this in some random slashdot posting. It's a particularly fast method of calculating an inverse square root. As for the best comment? It's a common one to be sure, but given that it's attached to the line that does the magic is what makes it great.

float Q_rsqrt( float number )
{
  long i;
  float x2, y;
  const float threehalfs = 1.5F;

  x2 = number * 0.5F;
  y  = number;
  i  = * ( long * ) &y;  // evil floating point bit level hacking
  i  = 0x5f3759df - ( i >> 1 ); // what the fuck?
  y  = * ( float * ) &i;
  y  = y * ( threehalfs - ( x2 * y * y ) ); // 1st iteration
  // y  = y * ( threehalfs - ( x2 * y * y ) ); // 2nd iteration, this can be removed

  #ifndef Q3_VM
  #ifdef __linux__
    assert( !isnan(y) ); // bk010122 - FPE?
  #endif
  #endif
  return y;
}
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