himadripal commented on code in PR #7021:
URL: https://github.com/apache/arrow-rs/pull/7021#discussion_r1946714937


##########
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);
+
+    if is_infallible_cast {
+        let mul = T::Native::from_decimal(10_i128)
+            .unwrap()
+            .pow_checked(delta_scale as u32)?;
+        let f = |x: T::Native| x.mul_wrapping(mul);
+        Ok(array.unary(f))
+    } else {
+        convert_to_bigger_or_equal_scale_decimal::<T, T>(

Review Comment:
   same here, only bypassing the validation based on this check inside 
`convert_to_bigger_or_equal_scale_decimal`?



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