aweltsch commented on code in PR #7021:
URL: https://github.com/apache/arrow-rs/pull/7021#discussion_r1948018718
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arrow-cast/src/cast/decimal.rs:
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@@ -121,6 +169,40 @@ where
})
}
+pub(crate) fn convert_to_bigger_or_equal_scale_decimal_same_type<T>(
+ array: &PrimitiveArray<T>,
+ input_precision: u8,
+ input_scale: i8,
+ output_precision: u8,
+ output_scale: i8,
+ cast_options: &CastOptions,
+) -> Result<PrimitiveArray<T>, ArrowError>
+where
+ T: DecimalType,
+ T::Native: DecimalCast + ArrowNativeTypeOp,
+{
+ let delta_scale = output_scale - input_scale;
+ // if the gain in precision (digits) is greater than the multiplication
due to scaling
+ // every number will fit into the output type
+ let is_infallible_cast = (input_precision as i8) + delta_scale <=
(output_precision as i8);
Review Comment:
I've looked into this a little bit more, and it seems that the precision and
scale are checked when building an array using the
`validate_decimal_precision_and_scale` function. My feeling is that the arrays
should always be constructed correctly, but anyway I added a the validation at
the top of the cast functions.
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