ALIGNED and UNALIGNED attributes
ALIGNED specifies that the data element is aligned on the storage boundary corresponding to its data type requirement. UNALIGNED specifies that each data element is mapped on the next byte boundary, except for fixed-length bit strings, which are mapped on the next bit.
Defaults are applied at element level. UNALIGNED is the default for bit data, character data, graphic data, uchar data, widechar data, and numeric character data. ALIGNED is the default for all other types of data.
Table 1 lists the requirements for the ALIGNED attribute.
Notes:
- Alignment and storage requirements for program control data can vary across supported systems.
- Complex data requires twice as much storage as its real counterpart, but the alignment requirements are the same.
| Variable type | Stored internally as: | Storage requirements (Bytes) | Alignment requirements | |
|---|---|---|---|---|
| ALIGNED data | UNALIGNED data | |||
| BIT (n) | ALIGNED: One byte for each group
of 8 bits (or part thereof) UNALIGNED: As many bits as are required, regardless of byte boundaries |
ALIGNED: CEIL(n/8) UNALIGNED: n bits |
Byte (Data can begin on any byte, 0 through 7) | Bit (Data can begin on any bit in any byte, 0 through 7) |
| CHARACTER (n) | One byte per character | n | Byte (Data can begin on any byte, 0 through 7) | Byte (Data can begin on any byte, 0 through 7) |
| CHARACTER (n)VARYINGZ | One byte per character plus one byte for the nullterminator | n+1 | ||
| GRAPHIC (n) | Two bytes per graphic | 2n | ||
| GRAPHIC (n) VARYINGZ | Two bytes per graphic plus two bytes for the nullterminator | 2n+2 | ||
| UCHAR (n) | Four bytes per uchar | 4n | ||
| UCHAR (n) VARYINGZ | Four bytes per uchar plus one byte for the nullterminator | 4n+1 | ||
| WIDECHAR (n) | Two bytes per widechar | 2n | ||
| WIDECHAR (n) VARYINGZ | Two bytes per widechar plus two bytes for the nullterminator | 2n+2 | ||
| PICTURE | One byte for each PICTURE character (except V, K, and the F scaling factor specification) | Number of PICTURE characters other than V, K, and F specification | ||
| DECIMAL FIXED (p,q) | Packed decimal format (1/2 byte per digit, plus 1/2 byte for sign) | CEIL((p+1)/2 | ||
| BINARY FIXED (p,q) SIGNED
1 <= p <= 7 UNSIGNED 1 <= p <= 8 |
One byte | 1 | ||
| ORDINAL SIGNED
1 <= p <= 7 UNSIGNED 1 <= p <= 8 |
||||
| BIT (n) VARYING | Two-byte prefix plus 1 byte for each group of 8 bits (or part thereof) of the declared maximum length | ALIGNED: 2+CEIL(n/8) UNALIGNED: 2 bytes+n bits |
Halfword (Data can begin on byte 0, 2, 4, or 6) | Byte (Data can begin on any byte, 0 through 7) |
| CHARACTER (n) VARYING | Two-byte prefix plus 1 byte per character of the declared maximum length | n+2 | ||
| GRAPHIC(n) VARYING | Two-byte prefix plus 2 bytes per graphic of the declared maximum length | 2n+2 | ||
| UCHAR (n) VARYING | Two-byte prefix plus 4 bytes per uchar of the declared maximum length | 4n+2 | ||
| WIDECHAR (n) VARYING | Two-byte prefix plus 2 bytes per widechar of the declared maximum length | 2n+2 | ||
| BINARY FIXED (p,q) SIGNED
8 <= p <= 15 UNSIGNED 9 <= p <= 16 |
Halfword | 2 | ||
| ORDINAL SIGNED
8 <= p <= 15 UNSIGNED 9 <= p <= 16 |
||||
| BINARY FIXED (p,q) SIGNED
16 <= p <= 31 UNSIGNED 17 <= p <= 32 |
Fullword | 4 | Fullword (Data can begin on byte 0 or 4) | Byte (Data can begin on any byte, 0 through 7) |
| ORDINAL SIGNED
16 <= p <= 31 UNSIGNED 17 <= p <= 32 |
||||
| BINARY FLOAT (p) 1<=p<=21 | Short floating-point | |||
| DECIMAL FLOAT (p) 1<=p<=6 if not DFP | ||||
| DECIMAL FLOAT (p) 1<=p<=7 if DFP | ||||
| BIT (n) VARYING4 | Four-byte prefix plus 1 byte for each group of 8 bits (or part thereof) of the declared maximum length | ALIGNED: 4+CEIL(n/8) UNALIGNED: 4 bytes+n bits | Fullword (Data can begin on byte 0 or 4) | Byte (Data can begin on any byte, 0 through 7) |
| CHARACTER (n) VARYING4 | Four-byte prefix plus 1 byte per character of the declared maximum length | n+4 | ||
| GRAPHIC (n) VARYING4 | Four-byte prefix plus 2 bytes per graphic of the declared maximum length | 2n+4 | ||
| UCHAR (n) VARYING4 | Four-byte prefix plus 4 bytes per uchar of the declared maximum length | 4n+4 | ||
| WIDECHAR (n) VARYING4 | Four-byte prefix plus 2 bytes per widechar of the declared maximum length | 2n+4 | ||
| POINTER(32) | – | 4 | ||
| HANDLE(32) | – | |||
| OFFSET under OFFSETSIZE(4) | – | |||
| FILE under LP(32) | – | |||
| ENTRY LIMITED under LP(32) | – | |||
| ENTRY | – | 8 | ||
| LABEL or FORMAT | – | |||
| TASK | – | 16 | ||
| AREA under OFFSETSIZE(4) | – | 16+size | Doubleword (Data can begin on byte 0) | AREA data cannot be unaligned |
| AREA under OFFSETSIZE(8) | – | 32+size | ||
| ENTRY LIMITED under LP(64) | – | 8 | Byte (Data can begin on any byte, 0 through 7) | |
| POINTER(64) | – | |||
| HANDLE(64) | – | |||
| OFFSET under OFFSETSIZE(8) | – | |||
| FILE under LP(64) | – | |||
| BINARY FIXED(p,q) SIGNED
32 <= p <= 63 UNSIGNED 33 <= p <= 64 |
– | |||
| BINARY FLOAT (p)
22 <= p <= 53 |
Long floating-point | |||
| DECIMAL FLOAT (p) 7<=p<=16 if not DFP | ||||
| DECIMAL FLOAT (p) 8<=p<=16 if DFP | ||||
| BINARY FLOAT (p)
54 <= p |
Extended floating-point | 16 | ||
| DECIMAL FLOAT (p) 17<=p | ||||
ALIGNED or UNALIGNED can be specified for element, array, structure, or union variables. The application of either attribute to a structure or union is equivalent to applying the attribute to all contained elements that are not explicitly declared ALIGNED or UNALIGNED.
The following example illustrates the effect of ALIGNED and UNALIGNED declarations for a structure and its elements:
declare 1 S,
2 X bit(2), /* unaligned by default */
2 A aligned, /* aligned explicitly */
3 B, /* aligned from A */
3 C unaligned, /* unaligned explicitly */
4 D, /* unaligned from C */
4 E aligned, /* aligned explicitly */
4 F, /* unaligned from C */
3 G, /* aligned from A */
2 H; /* aligned by default */