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  1. #include <stdio.h>
  2.  
  3. float Q_rsqrt( float number )
  4. {
  5. 	long i;
  6. 	float x2, y;
  7. 	const float threehalfs = 1.5F;
  8.  
  9. 	x2 = number * 0.5F;
  10. 	y  = number;
  11. 	i  = * ( long * ) &y;                       // evil floating point bit level hacking
  12. 	i  = 0x5f3759df - ( i >> 1 );               // what the fuck?
  13. 	y  = * ( float * ) &i;
  14. 	y  = y * ( threehalfs - ( x2 * y * y ) );   // 1st iteration
  15.       y  = y * ( threehalfs - ( x2 * y * y ) );   // 2nd iteration, this can be removed
  16.  
  17. 	return y;
  18. }
  19.  
  20. int main(void) {
  21. 	printf("%f\n", 1.0f/Q_rsqrt(144.0f)); // 12
  22. 	printf("%f\n", 1.0f/Q_rsqrt(289.0f)); // 17
  23. 	printf("%f\n", 1.0f/Q_rsqrt(25472209.0f)); // 5047
  24. 	printf("%f\n", 1.0f/Q_rsqrt(95775582.25f)); // 9786,5
  25. 	return 0;
  26. }
  27.  
Success #stdin #stdout 0s 2292KB
comments (?)
stdin
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Standard input is empty
stdout
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12.000025
17.000000
5047.015625
9786.516602
https://ideone.com/X2w19T
language:
C (gcc 8.3)
created:
10 years ago
visibility:
secret

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