# bitfield Field

The **\<bitfield>** is a container field, which allows wrapped member fields to be serialized using limited number of bits (instead of bytes). The supported fields, that can be members of the **\<bitfield>**, are:

* [\<enum>](/commsdsl-specification/fields/enum.md)
* [\<int>](/commsdsl-specification/fields/int.md)
* [\<set>](/commsdsl-specification/fields/set.md)

Since **v2** of the specification it is also allowed to use [\<ref>](/commsdsl-specification/fields/ref.md) field, which references one of the field types above.

The **\<bitfield>** field has all the [common](/commsdsl-specification/fields/common.md) properties as well as extra properties and elements described below.

## Member Fields

Member fields need to be listed as children XML elements of the **\<bitfield>**. Every such member is expected to use **bitLength** property to specify its serialization length **in bits**. If it is not specified, then length in bits is calculated automatically as length **in bytes** multiplied by **8**.

```
<?xml version="1.0" encoding="UTF-8"?>
<schema name="MyProtocol" endian="big">
    <fields>
        <bitfield name="SomeBitfield">
            <int name="SomeIntMember" type="uint8" bitLength="3" />
            <set name="SomeSetMember" bitLength="3">
                ...
            </set>
            <enum name="SomeEnumMember" type="uint8" bitLength="2">
                ...
            </enum>
        </bitfield>
    </fields>
</schema>
```

**NOTE** that summary of all the lengths in bits of all the members must be divisible by **8** and mustn't exceed **64** bits, otherwise the code generator must report an error.

The members of **\<bitfield>** must be listed in order starting from the **least** significant bit. In the example above *SomeIntMember* occupies bits \[0 - 2], *SomeSetMember* occupies bits \[3 - 5], and *SomeEnumMember* occupies bits \[6 -7].

If there is any other [property](/commsdsl-specification/properties.md) defined as XML child of the **\<bitfield>**, then all the members must be wrapped in **\<members>** XML element for separation.

```
<?xml version="1.0" encoding="UTF-8"?>
<schema name="MyProtocol" endian="big">
    <fields>
        <bitfield name="SomeBitfield">
            <displayName value="Proper Bitfield Name" />
            <members>
                <int name="SomeIntMember" type="uint8" bitLength="3" />
                <set name="SomeSetMember" bitLength="3">
                    ...
                </set>
                <enum name="SomeEnumMember" type="uint8" bitLength="2">
                    ...
                </enum>
            </members>
        </bitfield>
    </fields>
</schema>
```

## Endian

When serializing, the **\<bitfield>** object needs to combine the values of all the members into single unsigned raw value of appropriate length, and write the received value using appropriate endian. By default **endian** of the [schema](/commsdsl-specification/schema.md) is used, unless it is overridden using extra **endian** property of the **\<bitfield>** field.

```
<?xml version="1.0" encoding="UTF-8"?>
<schema name="MyProtocol" endian="big">
    <fields>
        <bitfield name="SomeBitfield" endian="little">
            ...
        </bitfield>
    </fields>
</schema>
```

Use [properties table](/commsdsl-specification/appendix/bitfield.md) for future references.


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