Records

A record allocation is the sum of the allocations of the fields in the fixed part and (if the record has them) the allocations of the tag field and the largest field in the variant part, plus trailing bits.

Field allocation depends on field type and whether the record is unpacked, packed, or crunched. The same factors determine field alignment. See the tables indicated below:

Table 5-4 Array Documentation Map

If the array is:	See:	In the section:
Unpacked	Table 5-1 “Allocation and Alignment of Unpacked Variables (HP Pascal Packing Algorithm) ”	“Unpacked Variables ”
Packed	Table 5-6 “Allocation and Alignment of Packed Record Fields (HP Pascal Packing Algorithm) ”	“Packed Records ”
Crunched	Table 5-7 “Allocation of Crunched Array Elements and Record Fields (HP Pascal Packing Algorithm) ”	“Crunched Arrays and Records ”

The HP Pascal packing algorithm uses these two rules to align a record:

The entire record is aligned on the same boundary as its most restricted field.
The variant part of a record is aligned on the same boundary as the most restricted first field of all variants.

Example

TYPE
   Rec = RECORD
            CASE b : Boolean OF
               TRUE  : (c : char;      {1 byte,  1-byte-aligned}
                        l : longreal;  {8 bytes, 8-byte-aligned}
                       );
               FALSE : (i : integer;   {4 bytes, 4-byte-aligned}
                       );
         END;

A record of the type Rec is 8-byte-aligned because its most restricted field, l, must be 8-byte-aligned.

The variant part of a record of type Rec is 4-byte-aligned, because the most restricted first field of the two variants, i, must be 4-byte-aligned.

A variable of type Rec is allocated 16 bytes. The TRUE and FALSE variants are aligned like this:

Figure 5-6 TRUE Variant

Figure 5-7 FALSE Variant

Sometimes you can reduce the space that a record takes by declaring its fields in different order.

Example

VAR
   upr1 : RECORD
             bf : Boolean;
             pf : 0..32767;
             cf : char;
          END;
 
   upr2 : RECORD
             bf : Boolean;
             cf : char;
             pf : 0..32767;
          END;

The only difference between the variables upr1 and upr2 is the order of their fields.

The variable upr1 takes six bytes:

Figure 5-8 Records Example 1

Because pf must be 2-byte-aligned, it cannot start in the second byte. The extra byte after cf is allocated because the most restricted element, pf, is 2-byte-aligned.

The variable upr2 takes four bytes:

Figure 5-9 Records Example 2

Sometimes you cannot reduce the space that a record takes by declaring its fields in different order.

Example

VAR
   pr1 : PACKED RECORD
            srf : 0..32;
            b : Boolean;
            pf : 0..32767;
            cf : char;
         END;
 
   pr2 : PACKED RECORD
            srf : 0..32;
            b : Boolean;
            cf : char;
            pf : 0..32767;
         END;

The only difference between the variables pr1 and pr2 is the order of their fields.

The variable pr1 takes four bytes:

Figure 5-10 Records Example 3

The variable pr2 also takes four bytes:

Figure 5-11 Records Example 4

Records

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