DC instruction—Offset constant

Use this constant to reserve storage for the offset into a storage area of an external dummy section, or the offset to a part or label in a class. The offset is entered into this space by the binder. The binder inserts the offset into a QY-type constant in 20 bit signed long-displacement format. When the offset is added to the address of an overall block of storage set aside for external dummy sections, it addresses the applicable section.

For a description of the use of the Q-type offset constant in combination with an external dummy section, see External dummy sections. See also Table 1 for details.

In the following example, to access the external dummy section named VALUE, the value of the constant labeled A is added to the base address of the block of storage allocated for external dummy sections.

A        DC              Q(VALUE)

The DXD, DSECT, or part names referenced in the Q-type offset constant need not be previously defined.

Table 1. Q offset constants
Subfield	Value	Example
1. Duplication factor	Allowed
2. Type	Q
3. Type Extension	D, Y
4. Program type	Allowed
5. Modifiers Implicit length: (length modifier not present)	Q-type: 4 bytes QD-type: 8 bytes QY-type: 3 bytes	Q(DXDEXT)
Alignment: (Length modifier not present)	Q-type: Fullword QD-type: Quadword QY-type: Halfword
Range for length:	Q-type: 1-4 bytes QD-type: 1-8 bytes QY-type: 3 bytes only (no bit length)	QL2(DXDEXT)
Range for scale:	Not allowed
Range for exponent:	Not allowed
6. Nominal value Represented by:	A DXD, DSECT, or part name (an external symbol)	`DC Q(DUMMYEXT) DC Q(DXDEXT)`
Enclosed by:	Parentheses
Exponent allowed:	No
Number of values per operand:	Multiple
Padding:	None
Truncation of assembled value:	Not applicable