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  1. /* package whatever; // don't place package name! */
  2.  
  3. import java.util.*;
  4. import java.lang.*;
  5. import java.io.*;
  6. import java.math.BigDecimal;
  7.  
  8. /* Name of the class has to be "Main" only if the class is public. */
  9. class Ideone
  10. {
  11.     /**
  12.      * Rounds a double to the specified number of decimal places using the ubiquitous "half up" rounding method
  13.      * @param numberToRound The number to be rounded
  14.      * @param numberOfDecimals The number of decimals to include in the rounded number
  15.      * @return The rounded number
  16.      */
  17.     public static double round(double numberToRound, int numberOfDecimals) {
  18.  
  19.         return new BigDecimal(numberToRound)
  20.                     .setScale(numberOfDecimals, BigDecimal.ROUND_HALF_UP)
  21.                     .doubleValue();
  22.     }
  23.  
  24.  
  25.     public static boolean checkDouble(long v) {
  26.     	double d = (v * 10 + 4) / 10000000.0;
  27.     	// v * 1,000,000 should be the same as round(d, 6) * 1000,000,000;
  28.     	double rescale = round(d, 6) * 1000000000.0;
  29.     	if (v * 1000.0 != rescale) {
  30.     		System.out.printf("Input %d/1000000.0 rounded to %.28f which rescaled to %.18f and not %f\n", v, round(d,6), rescale, v * 1000.0);
  31.     		return false;
  32.     	}
  33.     	return true;
  34.     }
  35.  
  36.     public static void main(String[] args) {
  37.         for (long i = 0; i < 1000000; i++) {
  38.         	if (!checkDouble(i)) {
  39.         		break;
  40.         	}
  41.  
  42.         }
  43. 	}
  44.  
  45.  }
Success #stdin #stdout 0.12s 320256KB
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stdin
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Standard input is empty
stdout
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Input 65/1000000.0 rounded to 0.0000650000000000000000000000 which rescaled to 64999.999999999990000000 and not 65000.000000
https://ideone.com/JlKsaB
language:
Java (HotSpot 12)
created:
9 years ago
visibility:
public

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