presto-hive/src/main/java/io/prestosql/plugin/hive/HiveDecimalParser.java/HiveDecimalParser/parseHiveDecimal
class HiveDecimalParser:    public static BigDecimal parseHiveDecimal(byte[] bytes, int start, int length, DecimalType columnType)
    {
        BigDecimal parsed = new BigDecimal(new String(bytes, start, length, UTF_8));
        if (parsed.scale() > columnType.getScale()) {
            // Hive rounds HALF_UP too
            parsed = parsed.setScale(columnType.getScale(), HALF_UP);
        }
        return rescale(parsed, columnType);
    }