parthchandra commented on code in PR #7021:
URL: https://github.com/apache/arrow-rs/pull/7021#discussion_r1946955287
##########
arrow-cast/src/cast/decimal.rs:
##########
@@ -76,6 +76,54 @@ where
}
}
+pub(crate) fn convert_to_smaller_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 = input_scale - output_scale;
+ // if the reudction of the input number through scaling (dividing) is
greater
Review Comment:
spelling: s/reudction/reduction
Also, can you add the example from the PR into this comment here. It makes
things absolutely clear.
##########
arrow-cast/src/cast/decimal.rs:
##########
@@ -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:
Have we already checked at this stage that the output precision is less than
or equal to the max allowed for decimal 128?
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