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Use HALF_EVEN rounding for the double type in generated code #142

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Use HALF_EVEN rounding for the double type in generated code #142

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e890e40
Use HALF_EVEN rounding for the double type in generated code
mbautin Jan 12, 2016
2b85dcb
Do not attempt to apply the "&" operator to a double
mbautin Jan 12, 2016
0c6f689
Do not apply the bit shift operation to double
mbautin Jan 12, 2016
e5269ff
Do not use the shift operator on a double in another place
mbautin Jan 12, 2016
b64ae1e
Fix MathFunctionsSuite with the updated rounding implementation (HALF…
mbautin Jan 12, 2016
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32 changes: 31 additions & 1 deletion sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/mathExpressions.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -764,12 +764,42 @@ case class Round(child: Expression, scale: Expression)
}"""
}
case DoubleType => // if child eval to NaN or Infinity, just return it.
// The logic for rounding half-integers to even values is exemplified by the following
// table:
//
// x | x rounded to half-even | x * 2 | (x rounded to half-even) * 2 | (x * 2) & 3
// ----------------------------------------------------------------------------------------
// -4.5 | -4 | -9 | -8 | 3
// -3.5 | -4 | -7 | -8 | 1
// -2.5 | -2 | -5 | -6 | 3
// -1.5 | -2 | -3 | -6 | 1
// -0.5 | 0 | -1 | 0 | 3
// 0.5 | 0 | 1 | 0 | 1
// 1.5 | 2 | 3 | 4 | 3
// 2.5 | 2 | 5 | 4 | 1
// 3.5 | 4 | 7 | 8 | 3
// 4.5 | 4 | 9 | 8 | 1
//
// Therefore, looking at the last three columns above, if x has the form of "<integer>.5",
// then
// (x rounded to half-even) * 2 = (x * 2) + ((x * 2) & 3) - 2

if (_scale == 0) {
s"""
if (Double.isNaN(${ce.primitive}) || Double.isInfinite(${ce.primitive})){
${ev.primitive} = ${ce.primitive};
} else {
${ev.primitive} = Math.round(${ce.primitive});
double timesTwo = ${ce.primitive} * 2;
long timesTwoRounded = Math.round(timesTwo);
if (timesTwo == timesTwoRounded) {
if ((timesTwoRounded & 1) == 0) {
${ev.primitive} = timesTwoRounded >> 1;
} else {
${ev.primitive} = (timesTwoRounded + (timesTwoRounded & 3) - 2) >> 1;
}
} else {
${ev.primitive} = Math.round(${ce.primitive});
}
}"""
} else {
s"""
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2 changes: 1 addition & 1 deletion ...atalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/MathFunctionsSuite.scala
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Expand Up @@ -512,7 +512,7 @@ class MathFunctionsSuite extends SparkFunSuite with ExpressionEvalHelper {
Seq.fill[Short](7)(31415)

val intResults: Seq[Int] = Seq(314000000, 314200000, 314160000, 314159000, 314159300,
314159270) ++ Seq.fill(7)(314159265)
314159260) ++ Seq.fill(7)(314159265)

val longResults: Seq[Long] = Seq(31415926536000000L, 31415926535900000L,
31415926535900000L, 31415926535898000L, 31415926535897900L, 31415926535897930L) ++
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