pTAL Guidelines for TAL Programmers

Coding Guidelines

pTAL Guidelines for TAL Programmers—527256-002

2-14

32-Bit Addresses

Guideline: Create 32-bit addresses only to reference data in extended data segments.

In TAL, your program can reference all data with a 16-bit address except data in

extended memory, for which you must use a 32-bit address. On TNS architecture, you

can also create 32-bit addresses to reference data in other segment types, such as in

the user data segment.

On native architecture, all addresses are 32 bits except addresses whose address type

is SGBADDR or SGWADDR, which are 16 bits on both TNS and native architectures.

Addresses and Integer Variables

Guideline: Do not store addresses and data in the same variable.

In TAL, you can declare a variable and store both integers and addresses in it.

Example 2-9 on page 2-14 is valid in TAL but not in pTAL.

To be compatible with pTAL, treat every pointer as having an object data type and an

address type. The object data type of a pointer is the data type of the objects that you

reference with the pointer such as INT, STRING, REAL(64), and so forth. The address

type of a pointer describes the addresses that you can store into the pointer.

For example, a STRING pointer that references data in the user data segment must

contain a byte address. Its address type is BADDR.

Address Variables

Guideline: Declare variables that hold addresses to be an address type.

pTAL defines new data types, all of which describe addresses. For details, see

Address-Type Variables on page 3-4.

Note. pTAL supports the ability to use 32-bit addresses to reference data in segments other

than extended data segments, but HP does not guarantee that pTAL will continue to support

this ability.

Example 2-9. Variable Can Store Integer or Address (TAL Only)

INT a[0:9];

INT i;

INT .p1;

INT .p2;

FOR i := 0 to 9 DO

a[i] := 0; ! i holds an integer loop-control variable

i := @p1; ! i holds an address

@p1 := @p2;

@p2 := i;