Function decimal_preimage_bounds

datafusion/functions/src/math/floor.rs:347–379

Compute preimage bounds for floor function on decimal types. For floor(x) = n, the preimage is [n, n+1). Returns None if: - The value has a fractional part (floor always returns integers) - Adding 1 would overflow

(
    value: D::Native,
    precision: u8,
    scale: i8,
)

/// - The value has a fractional part (floor always returns integers)
/// - Adding 1 would overflow
fn decimal_preimage_bounds<D: DecimalType>(
    value: D::Native,
    precision: u8,
    scale: i8,
) -> Option<(D::Native, D::Native)>
where
    D::Native: DecimalCast + ArrowNativeTypeOp + std::ops::Rem<Output = D::Native>,
{
    // Use rescale_decimal to compute "1" at target scale (avoids manual pow)
    // Convert integer 1 (scale=0) to the target scale
    let one_scaled: D::Native = rescale_decimal::<D, D>(
        D::Native::ONE, // value = 1
        1,              // input_precision = 1
        0,              // input_scale = 0 (integer)
        precision,      // output_precision
        scale,          // output_scale
    )?;

    // floor always returns an integer, so if value has a fractional part, there's no solution
    // Check: value % one_scaled != 0 means fractional part exists
    if scale > 0 && value % one_scaled != D::Native::ZERO {
        return None;
    }

    // Compute upper bound using checked addition
    // Before preimage stage, the internal i128/i256(value) is validated based on the precision and scale.
    // MAX_DECIMAL128_FOR_EACH_PRECISION and MAX_DECIMAL256_FOR_EACH_PRECISION are used to validate the internal i128/i256.
    // Any invalid i128/i256 will not reach here.
    // Therefore, the add_checked will always succeed if tested via SQL/SLT path.
    let upper = value.add_checked(one_scaled).ok()?;

    Some((value, upper))
}

#[cfg(test)]
mod tests {