HP 3000 Manuals HP 3000 Manuals
Packed Records
Table 5-4 shows how the HP Pascal packing algorithm allocates and
aligns the fields of a packed record. The field types are in
alphabetical order.
Table 5-4. Allocation and Alignment of Packed Record Fields
(HP Pascal Packing Algorithm)
-----------------------------------------------------------------------------------------------
| | | |
| Field Type | Allocation | Field Alignment |
| | | |
-----------------------------------------------------------------------------------------------
| | | |
| Anyptr | 8 bytes | 4-byte |
| | | |
-----------------------------------------------------------------------------------------------
| | | |
| Array, crunched | Minimum number of bits required to represent any | Bit |
| | value of the element type. | |
| | | |
-----------------------------------------------------------------------------------------------
| | | |
| Array, packed | Use formula in "Arrays" section and then pad to | Same as element |
| | alignment boundary. | or byte, |
| | | whichever is |
| | | larger. |
| | | |
-----------------------------------------------------------------------------------------------
| | | |
| Array, unpacked | Use formula in "Arrays" section and then pad to | Same as element. |
| | alignment boundary. | |
| | | |
-----------------------------------------------------------------------------------------------
| | | |
| Bit16 | 2 bytes | Bit |
| | | |
-----------------------------------------------------------------------------------------------
| | | |
| Bit32 | 4 bytes | 4-byte |
| | | |
-----------------------------------------------------------------------------------------------
| | | |
| Bit52 | 8 bytes | 4-byte |
| | | |
-----------------------------------------------------------------------------------------------
| | | |
| Boolean | 1 bit | Bit |
| | | |
-----------------------------------------------------------------------------------------------
| | | |
| Char | 1 byte | Bit |
| | | |
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| | |
| Enumeration | See "Enumerations and Subranges" . |
| | |
-----------------------------------------------------------------------------------------------
| | | |
| File | See "Files" . | 8-byte |
| | | |
-----------------------------------------------------------------------------------------------
| | | |
| Function | 8 bytes | 4-byte |
| | | |
-----------------------------------------------------------------------------------------------
| | | |
| Integer | 4 bytes | 4-byte |
| | | |
-----------------------------------------------------------------------------------------------
| | | |
| Globalanyptr | 8 bytes | 4-byte |
| | | |
-----------------------------------------------------------------------------------------------
| | | |
| Localanyptr | 4 bytes | 4-byte |
| | | |
-----------------------------------------------------------------------------------------------
| | | |
| Longint | 8 bytes | 4-byte |
| | | |
-----------------------------------------------------------------------------------------------
| | | |
| Longreal | 8 bytes | 8-byte |
| | | |
-----------------------------------------------------------------------------------------------
| | | |
| Pointer | 4 bytes | 4-byte |
| | | |
-----------------------------------------------------------------------------------------------
| | | |
| Procedure | 8 bytes | 4-byte |
| | | |
-----------------------------------------------------------------------------------------------
| | | |
| Real | 4 bytes | 4-byte |
| | | |
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Table 5-4. Allocation and Alignment of Packed Record Fields
(HP Pascal Packing Algorithm) (cont.)
-----------------------------------------------------------------------------------------------
| | | |
| Field Type | Allocation | Field Alignment |
| | | |
-----------------------------------------------------------------------------------------------
| | | |
| Record, packed | Fields are allocated by type, and record is padded | Largest alignment |
| | to the alignment boundary. | of any field or |
| | | byte, whichever |
| | | is larger. |
| | | |
-----------------------------------------------------------------------------------------------
| | | |
| Record, unpacked | Fields are allocated by type, and record is padded | Largest alignment |
| | to the alignment boundary. | of any field. |
| | | |
-----------------------------------------------------------------------------------------------
| | |
| Set | See "Sets" . |
| | |
-----------------------------------------------------------------------------------------------
| | | |
| Shortint | 2 bytes | 2-byte |
| | | |
-----------------------------------------------------------------------------------------------
| | | |
| Strings | See "Strings" . | 4-byte |
| | | |
-----------------------------------------------------------------------------------------------
| | |
| Subrange | See "Enumerations and Subranges" . |
| | |
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The field that is aligned on the largest boundary determines the
alignment of the entire record. For example, if a record has three
fields--one byte-aligned field, one 2-byte-aligned field, and one
4-byte-aligned field--the entire record is 4-byte-aligned.
Packing a record has no effect on fields that are unpacked structures.
Example
TYPE
ua = ARRAY [1..4] OF Boolean;
ur1 = RECORD
i : integer;
c : char;
END;
VAR
ur2 : RECORD
c : char;
a : ua;
r : ur1;
END;
pr : PACKED RECORD
c : char;
a : ua;
r : ur1;
END;
The fields in ur2 and pr are allocated and aligned identically.