/fast_inverse_square_root/fisr.c
C | 18 lines | 13 code | 3 blank | 2 comment | 0 complexity | eb1c03727cda77a4284b23bacd221383 MD5 | raw file
- // The following code is the fast inverse square root implementation from Quake III Arena, stripped of C preprocessor directives, but including the exact original comment text:[9]
- 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
- return y;
- }