Jefffrey commented on code in PR #10707:
URL: https://github.com/apache/arrow-rs/pull/10707#discussion_r3795376715
##########
arrow-cast/src/cast/mod.rs:
##########
@@ -348,6 +348,36 @@ pub fn cast(array: &dyn Array, to_type: &DataType) ->
Result<ArrayRef, ArrowErro
cast_with_options(array, to_type, &CastOptions::default())
}
+/// Convert an integer to a decimal native value without wrapping.
+///
+/// `AsPrimitive` / `as` silently truncates when the source is wider than `M`
+/// (for example `5_000_000_000i64 as i32`). All integer sources fit in `i128`
+/// losslessly, which [`DecimalCast`] then converts to the decimal native type
+/// with a range check.
+fn integer_to_decimal_native<I, M>(value: I) -> Option<M>
+where
+ I: Into<i128>,
+ M: DecimalCast,
+{
+ M::from_decimal(value.into())
+}
+
+/// Scale an integer down in its native type before narrowing it to the decimal
+/// native type.
+///
+/// If the scale factor cannot be represented by the input type, it is larger
+/// than every possible input value and integer division therefore produces
+/// zero.
+fn scale_integer_down<I>(value: I, scale: u32) -> Option<I>
+where
+ I: ArrowNativeTypeOp,
+{
+ match I::usize_as(10).pow_checked(scale) {
Review Comment:
this would push the pow into the hotloop which can impact performance i
believe
##########
arrow-cast/benches/integer_to_decimal.rs:
##########
Review Comment:
can we centralize these to existing cast kernels benchmarks:
https://github.com/apache/arrow-rs/blob/main/arrow/benches/cast_kernels.rs
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