[GitHub] [spark] mgaido91 commented on a change in pull request #21599: [SPARK-26218][SQL] Overflow on arithmetic operations returns incorrect result

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mgaido91 commented on a change in pull request #21599: [SPARK-26218][SQL] Overflow on arithmetic operations returns incorrect result
URL: https://github.com/apache/spark/pull/21599#discussion_r299659190
 
 

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 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/arithmetic.scala
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 @@ -129,17 +131,41 @@ abstract class BinaryArithmetic extends BinaryOperator with NullIntolerant {
   def calendarIntervalMethod: String =
     sys.error("BinaryArithmetics must override either calendarIntervalMethod or genCode")
 
+  def checkOverflowCode(result: String, op1: String, op2: String): String =
+    sys.error("BinaryArithmetics must override either checkOverflowCode or genCode")
+
   override def doGenCode(ctx: CodegenContext, ev: ExprCode): ExprCode = dataType match {
     case _: DecimalType =>
       defineCodeGen(ctx, ev, (eval1, eval2) => s"$eval1.$decimalMethod($eval2)")
     case CalendarIntervalType =>
       defineCodeGen(ctx, ev, (eval1, eval2) => s"$eval1.$calendarIntervalMethod($eval2)")
+    // In the following cases, overflow can happen, so we need to check the result is valid.
+    // Otherwise we throw an ArithmeticException
     // byte and short are casted into int when add, minus, times or divide
     case ByteType | ShortType =>
-      defineCodeGen(ctx, ev,
-        (eval1, eval2) => s"(${CodeGenerator.javaType(dataType)})($eval1 $symbol $eval2)")
+      nullSafeCodeGen(ctx, ev, (eval1, eval2) => {
+        val overflowCheck = if (checkOverflow) {
+          checkOverflowCode(ev.value, eval1, eval2)
+        } else {
+          ""
+        }
+        s"""
+           |${ev.value} = (${CodeGenerator.javaType(dataType)})($eval1 $symbol $eval2);
+           |$overflowCheck
+         """.stripMargin
+      })
     case _ =>
-      defineCodeGen(ctx, ev, (eval1, eval2) => s"$eval1 $symbol $eval2")
+      nullSafeCodeGen(ctx, ev, (eval1, eval2) => {
+        val overflowCheck = if (checkOverflow) {
+          checkOverflowCode(ev.value, eval1, eval2)
+        } else {
+          ""
+        }
+        s"""
+           |${ev.value} = $eval1 $symbol $eval2;
 
 Review comment:
   yes, this is good point actually. As I mentioned in https://github.com/apache/spark/pull/21599#issuecomment-505924180, the issue with this is that `addExact` exists only for few datatypes. So we should specialize many cases in the code here. So here we have a tradeoff between performances (in the check overflow case only) and code maintainability. What is your opinion on this?

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