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  1.     #include <stdio.h>
  2.     #include <stdint.h>
  3.  
  4.     double n0 = 0.5;
  5.     double n1 = -0.5;
  6.  
  7.     //special number, should round to zero
  8.     double n2 = 0.49999999999999994;
  9.     double n3 = -0.49999999999999994;
  10.  
  11.     int32_t round_naive( double n ) {
  12.  
  13.       return n + 0.5;
  14.     }
  15.  
  16.     int32_t round_less_naive( double n ) {
  17.  
  18.       return n > 0.0 ? n + 0.5 : n - 0.5;
  19.     }
  20.  
  21.     int32_t round_my_try( double n ){
  22.  
  23.       int32_t n2 = (int32_t)( n * 2.0 ); // double it
  24.       int bit = n2 & 0x1; // extract the half-bit
  25.       bit = n2 >> 31 ? -bit : bit; // check sign
  26.       return  n2/2 + bit; // adjust
  27.     }
  28.  
  29.     void test( double n ) {
  30.  
  31.       printf( "round_naive      ( %.17f ) -> %d\n", n, round_naive( n ) );
  32.       printf( "round_less_naive ( %.17f ) -> %d\n", n, round_less_naive( n ) );
  33.       printf( "round_my_try     ( %.17f ) -> %d\n\n", n, round_my_try( n ) );
  34.     }
  35.  
  36.     int main(void) {
  37.  
  38.       test( n0 );
  39.       test( n1 );
  40.       test( n2 );
  41.       test( n3 );
  42.  
  43.       return 0;
  44.     }
  45.  
  46.  
Success #stdin #stdout 0s 2168KB
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stdin
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Standard input is empty
stdout
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round_naive      ( 0.50000000000000000 ) -> 1
round_less_naive ( 0.50000000000000000 ) -> 1
round_my_try     ( 0.50000000000000000 ) -> 1

round_naive      ( -0.50000000000000000 ) -> 0
round_less_naive ( -0.50000000000000000 ) -> -1
round_my_try     ( -0.50000000000000000 ) -> -1

round_naive      ( 0.49999999999999994 ) -> 1
round_less_naive ( 0.49999999999999994 ) -> 1
round_my_try     ( 0.49999999999999994 ) -> 0

round_naive      ( -0.49999999999999994 ) -> 0
round_less_naive ( -0.49999999999999994 ) -> -1
round_my_try     ( -0.49999999999999994 ) -> 0
https://ideone.com/koDJi8
language:
C (clang 8.0)
created:
8 years ago
visibility:
public

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