quake3中求1/sqrt(x)的算法源代码

quake3中求1/sqrt(x)的算法源代码如下（未作任何修改）：

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 >>  );               // 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;
}