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  1. 	#include <cstdio>
  2. 	#include <cmath>
  3.  
  4.     //Print-format a 32-bit float by exploiting exponent
  5.     //Blog post: http://a...content-available-to-author-only...b.io/print-fp.html	
  6.  
  7. 	void print_fp( float number, int digits ) {
  8. 	    union {
  9. 	        float d;
  10. 	        int u;
  11. 	    };
  12.  
  13. 	    d = number;
  14.  
  15. 	    //deal with sign
  16. 	    bool minus = u >> 31; 
  17. 	    u = u & ~(1 << 31); 
  18.  
  19. 	    //calculate base-10 exponent
  20. 	    double exp = (u >> 23) - 127;
  21. 	    double exp10 = exp / log2( 10.0 );
  22.  
  23. 	    //adjust the number 
  24. 	    u = (u & ~(0xFF << 23)) | (127 << 23);
  25. 	    double d2 = double(d) * pow( 10.0, exp10 - int(exp10) ); 
  26. 	    if( d2 >= 10.0 ) { d2 = d2 / 10.0; exp10+=1.0; }
  27. 	    if( d2 < 1.0 ) { d2 = d2 * 10.0; exp10-=1.0; }
  28.  
  29. 	    //print sign
  30. 	    if( minus ) printf("-");
  31.  
  32. 	    //print integer part
  33. 	    int i = int( d2 );
  34. 	    printf("%.1d.", i);
  35. 	    d2 = d2 - i;
  36.  
  37. 	    while( digits-- ) { 
  38. 	        d2 = d2 * 10.0;
  39. 	        int i = int( d2 );
  40. 	        printf("%.1d", i);
  41. 	        d2 = d2 - i;
  42. 	    }
  43.  
  44. 	    //print exponent part
  45. 	    printf("e%d\n", int(exp10));
  46. 	}
  47.  
  48. 	int main() {
  49.  
  50. 		double d;
  51.  
  52. 	    d = 8.589973e9;
  53. 	    printf("%.10f\n", d);
  54. 	    print_fp( d , 10 );
  55.  
  56. 	    d = 8.589974e9;
  57. 	    printf("%.10f\n", d);
  58. 	    print_fp( d , 10 );
  59.  
  60. 	}
  61.  
Success #stdin #stdout 0s 3456KB
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stdin
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Standard input is empty
stdout
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8589973000.0000000000
8.5899735040e9
8589974000.0000000000
8.5899735040e9
https://ideone.com/QO1fU5
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
public

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