[jira] [Updated] (SPARK-13806) SQL round() produces incorrect results for negative values

["Mark Hamstra (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SPARK-13806?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Mark Hamstra updated SPARK-13806:
---------------------------------
    Description: 
Round in catalyst/expressions/mathExpressions.scala appears to be untested with negative values, and it doesn't handle them correctly.

There are at least two issues here:

First, in the genCode for FloatType and DoubleType with _scale == 0, round() will not produce the same results as for the BigDecimal.ROUND_HALF_UP strategy used in all other cases.  This is because Math.round is used for these _scale == 0 cases.  For example, Math.round(-3.5) is -3, while BigDecimal.ROUND_HALF_UP at scale 0 for -3.5 is -4. 

Even after this bug is fixed with something like...
{code}
if (${ce.value} < 0) {
  ${ev.value} = -1 * Math.round(-1 * ${ce.value});
} else {
  ${ev.value} = Math.round(${ce.value});
}
{code}
...which will allow an additional test like this to succeed in MathFunctionsSuite.scala:
{code}
checkEvaluation(Round(-3.5D, 0), -4.0D)
{code}
...there still appears to be a problem on at least the checkEvalutionWithUnsafeProjection path, where failures like this are produced:
{code}
Incorrect evaluation in unsafe mode: round(-3.141592653589793, -6), actual: [0,0], expected: [0,8000000000000000] (ExpressionEvalHelper.scala:145)
{code} 

  was:
Round in catalyst/expressions/mathExpressions.scala appears to be untested with negative values, and it doesn't handle them correctly.

There are at least two issues here:

1) In the genCode for FloatType and DoubleType with _scale == 0, round() will not produce the same results as for the BigDecimal.ROUND_HALF_UP strategy used in all other cases.  This is because Math.round is used for these _scale == 0 cases.  For example, Math.round(-3.5) is -3, while BigDecimal.ROUND_HALF_UP at scale 0 for -3.5 is -4. 

Even after this bug is fixed with something like...
{code}
if (${ce.value} < 0) {
  ${ev.value} = -1 * Math.round(-1 * ${ce.value});
} else {
  ${ev.value} = Math.round(${ce.value});
}
{code}
...which will allow an additional test like this to succeed in MathFunctionsSuite.scala:
{code}
checkEvaluation(Round(-3.5D, 0), -4.0D)
{code}
...there still appears to be a problem on at least the checkEvalutionWithUnsafeProjection path, where failures like this are produced:
{code}
Incorrect evaluation in unsafe mode: round(-3.141592653589793, -6), actual: [0,0], expected: [0,8000000000000000] (ExpressionEvalHelper.scala:145)
{code} 


> SQL round() produces incorrect results for negative values
> ----------------------------------------------------------
>
>                 Key: SPARK-13806
>                 URL: https://issues.apache.org/jira/browse/SPARK-13806
>             Project: Spark
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 1.6.0, 1.6.1, 2.0.0
>            Reporter: Mark Hamstra
>
> Round in catalyst/expressions/mathExpressions.scala appears to be untested with negative values, and it doesn't handle them correctly.
> There are at least two issues here:
> First, in the genCode for FloatType and DoubleType with _scale == 0, round() will not produce the same results as for the BigDecimal.ROUND_HALF_UP strategy used in all other cases.  This is because Math.round is used for these _scale == 0 cases.  For example, Math.round(-3.5) is -3, while BigDecimal.ROUND_HALF_UP at scale 0 for -3.5 is -4. 
> Even after this bug is fixed with something like...
> {code}
> if (${ce.value} < 0) {
>   ${ev.value} = -1 * Math.round(-1 * ${ce.value});
> } else {
>   ${ev.value} = Math.round(${ce.value});
> }
> {code}
> ...which will allow an additional test like this to succeed in MathFunctionsSuite.scala:
> {code}
> checkEvaluation(Round(-3.5D, 0), -4.0D)
> {code}
> ...there still appears to be a problem on at least the checkEvalutionWithUnsafeProjection path, where failures like this are produced:
> {code}
> Incorrect evaluation in unsafe mode: round(-3.141592653589793, -6), actual: [0,0], expected: [0,8000000000000000] (ExpressionEvalHelper.scala:145)
> {code} 



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