Function fixed_size_binary_substring

arrow-string/src/substring.rs:328–384

(
    array: &FixedSizeBinaryArray,
    old_len: usize,
    start: i64,
    length: Option<u64>,
)

}

fn fixed_size_binary_substring(
    array: &FixedSizeBinaryArray,
    old_len: usize,
    start: i64,
    length: Option<u64>,
) -> Result<ArrayRef, ArrowError> {
    let new_start = match start.cmp(&0) {
        Ordering::Greater => usize::try_from(start).unwrap_or(usize::MAX).min(old_len),
        Ordering::Equal => 0,
        Ordering::Less => {
            let offset = usize::try_from(start.unsigned_abs()).unwrap_or(usize::MAX);
            old_len.saturating_sub(offset)
        }
    };

    let new_len = match length {
        Some(len) => usize::try_from(len)
            .unwrap_or(usize::MAX)
            .min(old_len - new_start),
        None => old_len - new_start,
    };

    // build value buffer
    let num_of_elements = array.len();
    let data = array.value_data();
    let capacity = num_of_elements
        .checked_mul(new_len)
        .expect("capacity overflow");
    let mut new_values = MutableBuffer::new(capacity);
    (0..num_of_elements)
        .map(|idx| {
            let offset = idx * array.value_size();
            (offset + new_start, offset + new_start + new_len)
        })
        .for_each(|(start, end)| new_values.extend_from_slice(&data[start..end]));

    let mut nulls = array
        .nulls()
        .map(|n| n.inner().sliced())
        .and_then(|b| NullBuffer::from_unsliced_buffer(b, num_of_elements));

    if new_len == 0 && nulls.is_none() {
        // FixedSizeBinaryArray::new takes length from the values buffer, except when size == 0.
        // In that case it uses the null buffer length, so preserve the original length here.
        // Example: ["", "", ""] -> substring(..., 1, Some(2)) should keep len=3;
        // otherwise it collapses to an empty array (len=0).
        nulls = Some(NullBuffer::new_valid(num_of_elements));
    }

    let new_len: i32 = new_len.try_into().expect("new_len overflow");

    Ok(Arc::new(FixedSizeBinaryArray::new(
        new_len,
        new_values.into(),
        nulls,
    )))
}