Function fold_decimal_chunk 

fn fold_decimal_chunk<T: DecimalType>(
    value: T::Native,
    chunk: u64,
    chunk_len: usize,
    negative: bool,
) -> Result<T::Native, DecimalParseError>

Folds a chunk of up to MAX_CHUNK_DIGITS digits into value, producing value * 10^chunk_len + chunk (chunk is negated first when parsing a negative number).