# Bit Fields tutorial
In this tutorial, you will learn how to enhance disassembly output by using bitfields.
Suppose the source code looked like this:
```
// 'flags' parameter is combination of the following bits:
// (don't use OOF_SIGNMASK and OOF_WIDTHMASK, they are for the kernel)
#define OOF_SIGNMASK 0x0003 // sign output:
#define OOFS_IFSIGN 0x0000 // output sign if needed
#define OOFS_NOSIGN 0x0001 // should not out sign ()
#define OOFS_NEEDSIGN 0x0002 // always out sign (+-)
#define OOF_SIGNED 0x0004 // output as signed if
int m65_opflags(const op_t &x)
{
switch ( x.type )
{
case o_displ:
return OOF_ADDR|OOFS_NOSIGN|OOFW_16;
case o_near:
case o_mem:
return OOF_ADDR|OOF_NUMBER|OOFS_NOSIGN|OOFW_16|OOF_ZSTROFF;
default:
return 0;
}
}
```
We have a disassembly that looks like this:
Let’s improve it by using bitfields.
1. We first define a bitfield type by going to the Local types window (menu Open subviews -> Local types). We press Ins to add a new enum and make it a bitfield. The name given to the bitfield does not matter much.
Note that **Bitmask** has been checked. Click OK.
2. Then we edit the enum and update it using the C syntax tab as shown in the screenshot below.
Click OK.
The first bitfield mask is 3 (or 2 bits). The name of the mask is not used by IDA, it is intended as a memory helper. The enum definition becomes:
3. We finally switch to the disassembly window. Through the Edit -> Operand types -> Enum member menu (or by pressing M on the second operand at addresses 0x130003E39 and 0x130003E40) we select the enum type we just defined and get this result…
That’s all folks!