Packed Records

Table 5-6 “Allocation and Alignment of Packed Record Fields (HP Pascal Packing Algorithm) ” shows how the HP Pascal packing algorithm allocates and aligns the fields of a packed record. The field types are in alphabetical order.

Table 5-6 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 value of the element type.	Bit
Array, packed	Use formula in “Arrays ” section and then pad to alignment boundary.	Same as element or byte, whichever is larger.
Array, unpacked	Use formula in “Arrays ” section and then pad to alignment boundary.	Same as element.
Bit16	2 bytes	Bit
Bit32	4 bytes	4-byte
Bit52	8 bytes	4-byte
Boolean	1 bit	Bit
Char	1 byte	Bit
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
Record, packed	Fields are allocated by type, and record is padded to the alignment boundary.	Largest alignment of any field or byte, whichever is larger.
Record, unpacked	Fields are allocated by type, and record is padded to the alignment boundary.	Largest alignment of any field.
Set	See “Sets ”.
Shortint	2 bytes	2-byte
Strings	See “Strings ”.	4-byte
Subrange	See “Enumerations and Subranges ”.

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.

Packed Records

Technical documentation

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