let canonical_hex = "18000000136400F2AF967ED05C82DE3297FF6FDE3
let canonical = hex::decode(canonical_hex.clone()).unwrap();  
let doc = Document::from_reader(canonical.as_slice()).unwrap()
let expected = doc.get_decimal128("d").unwrap().clone();      
                                                                                       
let roundstring = Decimal128::from_str(expected.to_string().as_str());
assert_eq!(roundstring, expected); // succeeds                
                                                              
let manual_expected = doc! { "d": Bson::Decimal128(expected) }
assert_eq!(manual_expected, doc); // succeeds                 
                                                              
let mut manual_expected_bytes = Vec::new();                   
manual_expected.to_writer(&mut manual_expected_bytes).unwrap()
assert_eq!(hex::encode(manual_expected_bytes), canonical_hex); // succeeds
                                                              
let manual = doc! { "d": Bson::Decimal128(roundstring) };     
assert_eq!(manual, doc); // also succeeds                     
                                                              
let mut manual_bytes = Vec::new();                            
manual.to_writer(&mut manual_bytes).unwrap();                 
assert_eq!(hex::encode(manual_bytes), canonical_hex); // fails
assert_eq!(expected.to_string(), "-1234567890123456789012345678901234"); // also fails