Function output_scale_for_decimal

datafusion/functions/src/math/round.rs:42–60

(precision: u8, input_scale: i8, decimal_places: i32)

use std::sync::Arc;

fn output_scale_for_decimal(precision: u8, input_scale: i8, decimal_places: i32) -> i8 {
    // `decimal_places` controls the maximum output scale, but scale cannot exceed the input scale.
    //
    // For negative-scale decimals, allow further scale reduction to match negative `decimal_places`
    // (e.g. scale -2 rounded to -3 becomes scale -3). This preserves fixed precision by
    // representing the rounded result at a coarser scale.
    if input_scale < 0 {
        // Decimal scales must be within [-precision, precision] and fit in i8. For negative-scale
        // decimals, allow rounding to move the output scale further negative, but cap it at
        // `-precision` (beyond that, the rounded result is always 0).
        let min_scale = -i32::from(precision);
        let new_scale = i32::from(input_scale).min(decimal_places).max(min_scale);
        return new_scale as i8;
    }

    // The `min` ensures the result is always within i8 range because `input_scale` is i8.
    let decimal_places = decimal_places.max(0);
    i32::from(input_scale).min(decimal_places) as i8
}

fn normalize_decimal_places_for_decimal(
    decimal_places: i32,