传说中很快的浮点数开根号算法

float Q_rsqrt( float number )
02 {
03 long i;
04 float x2, y;
05 const float threehalfs = 1.5F;
06
07 x2 = number * 0.5F;
08 y = number;
09 i = * ( long * ) &y; // evil floating point bit level hacking
10 i = 0x5f375a86 - ( i >> 1);//0x5f3759df - ( i >> 1 ); // what the fuck?
11 y = * ( float * ) &i;
12 y = y * ( threehalfs - ( x2 * y * y ) ); // 1st iteration
13 // y = y * ( threehalfs - ( x2 * y * y ) ); // 2nd iteration, this can be removed
14
15 #ifndef Q3_VM
16 #ifdef __linux__
17 assert( !isnan(y) ); // bk010122 - FPE?
18 #endif
19 #endif
20 return y;
21 }