我也在寻找呀！

搜索  卡马克

搜索  卡马克

:)

google "doom fast inverse square root"

and let me post it here:

1. 
   
2. float Q_rsqrt( float number )
   
3. {
   
4.         long i;
   
5.         float x2, y;
   
6.         const float threehalfs = 1.5F;
   
7. 
   
8.         x2 = number * 0.5F;
   
9.         y  = number;
   
10.         i  = * ( long * ) &y;                       // evil floating point bit level hacking
    
11.         i  = 0x5f3759df - ( i >> 1 );               // what the fuck?
    
12.         y  = * ( float * ) &i;
    
13.         y  = y * ( threehalfs - ( x2 * y * y ) );   // 1st iteration
    
14. //      y  = y * ( threehalfs - ( x2 * y * y ) );   // 2nd iteration, this can be removed
    
15. 
    
16.         return y;
    
17. }

复制代码This is probably the most fascinating piece of code anyone has written over the last 50 years. Bar none.

and we still don't know who exactly wrote it, and how s/he came up with the magic number.

enjoy.

这个必须mark，记得以前也看过，是一个大神创造的那个magic number。

整形还是浮点数？