DigitList bug in recent patch

Frank Ding dingxmin at linux.vnet.ibm.com
Wed Mar 27 07:48:23 UTC 2013

Hi guys,
   We noticed there is a recent change (patch @ 
http://hg.openjdk.java.net/jdk8/jdk8/jdk/rev/bc1f16f5566f ) that changed 
the behavior of the following program.

import java.math.RoundingMode;
public class TestNumberFormat {

     public static void main(String[] args) {

         java.text.NumberFormat numberFormat = 
         double v = 78.00005;
         String ret = numberFormat.format(v);

Note the rounding mode HALF_EVEN and the expected output should be "78" 
which can also be verified by running previous jdk (before b73).

Stepping into code and the suspicious code is in 
DigitList.shouldRoundUp().  allDecimalDigits is false so true is 
returned, causing the last digit in fraction part to be 1.
             case HALF_EVEN:
                 // Implement IEEE half-even rounding
                 if (digits[maximumDigits] > '5') {
                     return true;
                 } else if (digits[maximumDigits] == '5' ) {
                     if (maximumDigits == (count - 1)) {
                         // the rounding position is exactly the last 
index :
                         if (alreadyRounded)
                             // If FloatingDecimal rounded up (value was 
below tie),
                             // then we should not round up again.
                             return false;

                         if (!allDecimalDigits)
                             // Otherwise if the digits dont represent 
exact value,
                             // value was above tie and FloatingDecimal 
                             // digits to tie. We must round up.
                             return true;

Since I am not familiar of the numeric conversion, can any one shed your 
light on it?

Best regards,

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