DigitList bug in recent patch

[Frank Ding]

Current JDK gives the output of "78.0001".

Best regards,
Frank

On 3/27/2013 3:48 PM, Frank Ding wrote:
> 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 = 
> java.text.NumberFormat.getInstance(
>                 java.util.Locale.US);
>         double v = 78.00005;
>         numberFormat.setMaximumFractionDigits(4);
>         numberFormat.setRoundingMode(RoundingMode.HALF_EVEN);
>         numberFormat.setMinimumFractionDigits(0);
>         numberFormat.setGroupingUsed(false);
>         String ret = numberFormat.format(v);
>         System.out.println(ret);
>     }
> }
>
> 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 
> truncated
>                             // 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,
> Frank