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new 7a874616e docs: document negative zero cast-to-string incompatibility
(#3811)
7a874616e is described below
commit 7a874616e88e51115ca3c51ba12fa7991386759f
Author: Andy Grove <[email protected]>
AuthorDate: Fri Mar 27 13:40:57 2026 -0600
docs: document negative zero cast-to-string incompatibility (#3811)
---
docs/source/user-guide/latest/compatibility.md | 7 +++++++
.../main/scala/org/apache/comet/expressions/CometCast.scala | 1 +
spark/src/main/scala/org/apache/comet/serde/arrays.scala | 13 +++++++++++--
3 files changed, 19 insertions(+), 2 deletions(-)
diff --git a/docs/source/user-guide/latest/compatibility.md
b/docs/source/user-guide/latest/compatibility.md
index e0bc5f06e..3ec665618 100644
--- a/docs/source/user-guide/latest/compatibility.md
+++ b/docs/source/user-guide/latest/compatibility.md
@@ -153,6 +153,13 @@ Cast operations in Comet fall into three levels of support:
Spark.
- **N/A**: Spark does not support this cast.
+### Negative Zero
+
+When casting floating-point values to strings, Spark normalizes negative zero
(`-0.0`) to `"0.0"`, but Comet
+may produce `"-0.0"`. Since negative zero and positive zero are semantically
equivalent (`-0.0 == 0.0` is true
+in IEEE 754), this difference is unlikely to affect real-world results. See
+[#1036](https://github.com/apache/datafusion-comet/issues/1036) for more
details.
+
### Legacy Mode
<!--BEGIN:CAST_LEGACY_TABLE-->
diff --git a/spark/src/main/scala/org/apache/comet/expressions/CometCast.scala
b/spark/src/main/scala/org/apache/comet/expressions/CometCast.scala
index d50aa5d8d..2188f8e9a 100644
--- a/spark/src/main/scala/org/apache/comet/expressions/CometCast.scala
+++ b/spark/src/main/scala/org/apache/comet/expressions/CometCast.scala
@@ -149,6 +149,7 @@ object CometCast extends CometExpressionSerde[Cast] with
CometExprShim {
isSupported(dt.elementType, dt1.elementType, timeZoneId, evalMode)
case (dt: DataType, _) if dt.typeName == "timestamp_ntz" =>
// https://github.com/apache/datafusion-comet/issues/378
+ // https://github.com/apache/datafusion-comet/issues/3179
toType match {
case DataTypes.TimestampType | DataTypes.DateType |
DataTypes.StringType =>
Incompatible()
diff --git a/spark/src/main/scala/org/apache/comet/serde/arrays.scala
b/spark/src/main/scala/org/apache/comet/serde/arrays.scala
index 5d10ff8a3..47a6e9142 100644
--- a/spark/src/main/scala/org/apache/comet/serde/arrays.scala
+++ b/spark/src/main/scala/org/apache/comet/serde/arrays.scala
@@ -247,7 +247,12 @@ object CometArrayMin extends
CometExpressionSerde[ArrayMin] {
object CometArraysOverlap extends CometExpressionSerde[ArraysOverlap] {
- override def getSupportLevel(expr: ArraysOverlap): SupportLevel =
Incompatible(None)
+ override def getSupportLevel(expr: ArraysOverlap): SupportLevel =
+ Incompatible(
+ Some(
+ "Inconsistent behavior with NULL values" +
+ " (https://github.com/apache/datafusion-comet/issues/3645)" +
+ " (https://github.com/apache/datafusion-comet/issues/2036)"))
override def convert(
expr: ArraysOverlap,
@@ -446,7 +451,11 @@ object CometArrayInsert extends
CometExpressionSerde[ArrayInsert] {
object CometArrayUnion extends CometExpressionSerde[ArrayUnion] {
- override def getSupportLevel(expr: ArrayUnion): SupportLevel =
Incompatible(None)
+ override def getSupportLevel(expr: ArrayUnion): SupportLevel =
+ Incompatible(
+ Some(
+ "Correctness issue" +
+ " (https://github.com/apache/datafusion-comet/issues/3644)"))
override def convert(
expr: ArrayUnion,
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