native/spark-expr/src/math_funcs/internal/make_decimal.rs

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// to you under the Apache License, Version 2.0 (the
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//
//   http://www.apache.org/licenses/LICENSE-2.0
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use crate::math_funcs::utils::get_precision_scale;
use arrow::datatypes::DataType;
use arrow::{
    array::{AsArray, Decimal128Builder},
    datatypes::{validate_decimal_precision, Int64Type},
};
use datafusion::common::{internal_err, Result as DataFusionResult, ScalarValue};
use datafusion::physical_plan::ColumnarValue;
use std::sync::Arc;

/// Spark-compatible `MakeDecimal` expression (internal to Spark optimizer)
pub fn spark_make_decimal(
    args: &[ColumnarValue],
    data_type: &DataType,
) -> DataFusionResult<ColumnarValue> {
    let (precision, scale) = get_precision_scale(data_type);
    match &args[0] {
        ColumnarValue::Scalar(v) => match v {
            ScalarValue::Int64(n) => Ok(ColumnarValue::Scalar(ScalarValue::Decimal128(
                long_to_decimal(n, precision, scale),
                precision,
                scale,
            ))),
            sv => internal_err!("Expected Int64 but found {sv:?}"),
        },
        ColumnarValue::Array(a) => match a.data_type() {
            DataType::Int64 => {
                let arr = a.as_primitive::<Int64Type>();
                let mut result = Decimal128Builder::new();
                for v in arr.into_iter() {
                    result.append_option(long_to_decimal(&v, precision, scale))
                }
                let result_type = DataType::Decimal128(precision, scale);

                Ok(ColumnarValue::Array(Arc::new(
                    result.finish().with_data_type(result_type),
                )))
            }
            av => internal_err!("Expected Int64 but found {av:?}"),
        },
    }
}

/// Convert the input long to decimal with the given maximum precision. If overflows, returns null
/// instead.
#[inline]
fn long_to_decimal(v: &Option<i64>, precision: u8, scale: i8) -> Option<i128> {
    match v {
        Some(v) if validate_decimal_precision(*v as i128, precision, scale).is_ok() => {
            Some(*v as i128)
        }
        _ => None,
    }
}