Fast Inverse Square Root Without Pointer Casting

fastinvsqrt.c

/* See http://en.wikipedia.org/wiki/Fast_inverse_square_root for 
   For original implementation
*/

typedef union {
    long  l;
    float f;
} LongFloat;

static inline float InvSqrt( const float v ) {
    LongFloat i, x2, y;
    const float threehalfs = 1.5f;
    
    x2.f = v * 0.5f;
    y.f  = v;
    i.f  = y.f;                      // evil floating point bit level hacking
    i.l  = 0x5f3759df - ( i.l >> 1 );                       // what the fuck?
    y.f  = i.f;
    y.f  = y.f * ( threehalfs - ( x2.f * y.f * y.f ) );     // 1st iteration
    y.f  = y.f * ( threehalfs - ( x2.f * y.f * y.f ) );     // 2nd iteration
    
    return y.f;
}