卡马克和快速平方根

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; 
}