viirya commented on code in PR #4136:
URL: https://github.com/apache/arrow-rs/pull/4136#discussion_r1180064607
##########
arrow-arith/src/arithmetic.rs:
##########
@@ -1434,6 +1434,100 @@ pub fn multiply_dyn_checked(
}
}
+#[cfg(feature = "dyn_arith_dict")]
+fn get_precision_scale(dt: &DataType) -> Result<(u8, i8), ArrowError> {
+ match dt {
+ DataType::Decimal128(precision, scale) => Ok((*precision, *scale)),
+ _ => Err(ArrowError::ComputeError(
+ "Cannot get precision and scale from non-decimal type".to_string(),
+ )),
+ }
+}
+
+#[cfg(feature = "dyn_arith_dict")]
+/// Perform `left * right` operation on two decimal arrays. If either left or
right value is
+/// null then the result is also null.
+///
+/// This performs decimal multiplication which allows precision loss if an
exact representation
+/// is not possible for the result, according to the required scale. In the
case, the result
+/// will be rounded to the required scale.
+///
+/// If the required scale is greater than the product scale, an error is
returned.
+///
+/// This doesn't detect overflow. Once overflowing, the result will wrap
around.
+///
+/// It is implemented for compatibility with precision loss `multiply`
function provided by
+/// other data processing engines. For multiplication with precision loss
detection, use
+/// `multiply_dyn` or `multiply_dyn_checked` instead.
+pub fn multiply_fixed_point_dyn(
+ left: &dyn Array,
+ right: &dyn Array,
+ required_scale: i8,
+) -> Result<ArrayRef, ArrowError> {
+ match (left.data_type(), right.data_type()) {
+ (
+ DataType::Dictionary(_, lhs_value_type),
+ DataType::Dictionary(_, rhs_value_type),
+ ) if matches!(lhs_value_type.as_ref(), &DataType::Decimal128(_, _))
+ && matches!(rhs_value_type.as_ref(), &DataType::Decimal128(_, _))
=>
+ {
+ downcast_dictionary_array!(
+ left => match left.values().data_type() {
+ DataType::Decimal128(_, _) => {
+ let lhs_precision_scale =
get_precision_scale(lhs_value_type.as_ref())?;
Review Comment:
Added a function for that.
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