viirya commented on code in PR #4088:
URL: https://github.com/apache/arrow-rs/pull/4088#discussion_r1167054727
##########
arrow-cast/src/cast.rs:
##########
@@ -2081,29 +2081,102 @@ impl DecimalCast for i256 {
}
}
-fn cast_decimal_to_decimal<I, O>(
- array: &PrimitiveArray<I>,
- input_scale: i8,
+fn cast_decimal_to_decimal_error<O>(
output_precision: u8,
output_scale: i8,
- cast_options: &CastOptions,
-) -> Result<ArrayRef, ArrowError>
+) -> impl Fn(<O as ArrowPrimitiveType>::Native) -> ArrowError
where
- I: DecimalType,
O: DecimalType,
- I::Native: DecimalCast + ArrowNativeTypeOp,
O::Native: DecimalCast + ArrowNativeTypeOp,
{
- let error = |x| {
+ move |x: O::Native| {
ArrowError::CastError(format!(
"Cannot cast to {}({}, {}). Overflowing on {:?}",
O::PREFIX,
output_precision,
output_scale,
x
))
+ }
+}
+
+fn cast_decimal_to_decimal_same_type<T>(
+ array: &PrimitiveArray<T>,
+ input_scale: i8,
+ output_precision: u8,
+ output_scale: i8,
+ cast_options: &CastOptions,
+) -> Result<ArrayRef, ArrowError>
+where
+ T: DecimalType,
+ T::Native: DecimalCast + ArrowNativeTypeOp,
+{
+ let error = cast_decimal_to_decimal_error::<T>(output_precision,
output_scale);
+
+ let array: PrimitiveArray<T> = if input_scale == output_scale {
+ // the scale doesn't change, the native value don't need to be changed
+ array.clone()
+ } else if input_scale > output_scale {
+ let div = T::Native::from_decimal(10_i128)
+ .unwrap()
+ .pow_checked((input_scale - output_scale) as u32)?;
+
+ let half = div.div_wrapping(T::Native::from_usize(2).unwrap());
+ let half_neg = half.neg_wrapping();
+
+ let f = |x: T::Native| {
+ // div is >= 10 and so this cannot overflow
+ let d = x.div_wrapping(div);
+ let r = x.mod_wrapping(div);
+
+ // Round result
+ let adjusted = match x >= T::Native::ZERO {
+ true if r >= half => d.add_wrapping(T::Native::ONE),
+ false if r <= half_neg => d.sub_wrapping(T::Native::ONE),
+ _ => d,
+ };
+ Some(adjusted)
+ };
+
+ match cast_options.safe {
+ true => array.unary_opt(f),
+ false => array.try_unary(|x| f(x).ok_or_else(|| error(x)))?,
+ }
+ } else {
+ // input_scale > output_scale
Review Comment:
```suggestion
// input_scale < output_scale
```
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