Crunched Arrays and Records

Crunched packing, a systems programming extension, packs a record or array as tightly as possible: it bit-aligns every field or element.

Table 5-7 “Allocation of Crunched Array Elements and Record Fields (HP Pascal Packing Algorithm) ” shows how the HP Pascal packing algorithm allocates elements of crunched arrays or fields of crunched records. If a type is not in Table 5-7 “Allocation of Crunched Array Elements and Record Fields (HP Pascal Packing Algorithm) ”, a crunched array or record cannot have elements or fields of that type.

Table 5-7 Allocation of Crunched Array Elements and Record Fields (HP Pascal Packing Algorithm)

( Minimum number of bits required to represent value.)

The value representation has the most significant bit first and the least significant bit last (no byte swapping).
If a record or array contains a crunched structure, it must be crunched itself.
The value zero is always included in the subrange when calculating the minimum number of bits; for example, this record takes seven bits:
CRUNCHED RECORD f : 100..101; END;
If any element can be negative, an extra bit is allocated for the sign; for example, this record takes three bits:
CRUNCHED RECORD f : -4..3; END;

Example

A record that is defined:

TYPE
   u_rec = RECORD         {4-byte aligned}
      a,b : Boolean;
      c : char;
      d : minint..maxint;
      e : Boolean;
   END;

is allocated and aligned this way:

Figure 5-14 Crunched Arrays and Records Example 1

A record that is defined:

TYPE
p_rec1 = PACKED RECORD  {Byte-aligned}
   a,b : Boolean;
   c : char;
   d : minint..maxint;
   e : Boolean;
END;

is allocated and aligned this way:

Figure 5-15 Crunched Arrays and Records Example 2

A record that is defined:

p_rec2 = PACKED RECORD {4-byte-aligned}
   a,b : Boolean;
   c : char;
   d : integer;
   e : Boolean;
END;

is allocated and aligned this way:

Figure 5-16 Crunched Arrays and Records Example 3

A record that is defined:

TYPE
   c_rec1 = CRUNCHED RECORD
      a,b : Boolean;
      c   : char;
      d   : minint..maxint;
      e   : Boolean
   END;

Or:

TYPE
   c_rec2 = CRUNCHED RECORD
      a,b : Boolean;
      c   : char;
      d   : integer;
      e   : Boolean
   END;

is allocated and aligned this way:

Figure 5-17 Crunched Arrays and Records Example 4

The bits containing question marks are not allocated if the type is used inside another crunched structure.

Technical documentation