Function lpad_impl

datafusion/functions/src/unicode/lpad.rs:365–506

(
    string_array: &V,
    length_array: &Int64Array,
    fill_array: Option<V2>,
)

}

fn lpad_impl<'a, V, V2, T>(
    string_array: &V,
    length_array: &Int64Array,
    fill_array: Option<V2>,
) -> Result<ArrayRef>
where
    V: StringArrayType<'a>,
    V2: StringArrayType<'a>,
    T: OffsetSizeTrait,
{
    let array = if let Some(fill_array) = fill_array {
        let mut builder: GenericStringBuilder<T> = GenericStringBuilder::new();
        let mut fill_chars_buf = Vec::new();

        for ((string, target_len), fill) in string_array
            .iter()
            .zip(length_array.iter())
            .zip(fill_array.iter())
        {
            if let (Some(string), Some(target_len), Some(fill)) =
                (string, target_len, fill)
            {
                if target_len > i32::MAX as i64 {
                    return exec_err!(
                        "lpad requested length {target_len} too large, maximum allowed length is {}",
                        i32::MAX
                    );
                }

                let target_len = if target_len < 0 {
                    0
                } else {
                    target_len as usize
                };
                if target_len == 0 {
                    builder.append_value("");
                    continue;
                }

                if string.is_ascii() && fill.is_ascii() {
                    // ASCII fast path: byte length == character length.
                    let str_len = string.len();
                    if target_len < str_len {
                        builder.append_value(&string[..target_len]);
                    } else if fill.is_empty() {
                        builder.append_value(string);
                    } else {
                        let pad_len = target_len - str_len;
                        let fill_len = fill.len();
                        let full_reps = pad_len / fill_len;
                        let remainder = pad_len % fill_len;
                        for _ in 0..full_reps {
                            builder.write_str(fill)?;
                        }
                        if remainder > 0 {
                            builder.write_str(&fill[..remainder])?;
                        }
                        builder.append_value(string);