TAL Programmer's Guide

Using Simple Pointers

Using Pointers

9–4 096254 Tandem Computers Incorporated

The following table shows the kinds of global variables to which you can apply the @

operator:

Variable @identifier?

Direct array Yes

Standard indirect array Yes

Extended indirect array No

Direct structure Yes

Standard indirect structure Yes

Extended indirect structure No

Simple pointer No

Structure pointer No

For example, you can initialize a global standard simple pointer with the address of an

array element:

STRING .array[0:3]; !Declare ARRAY

STRING .string_ptr := @array[3];

!Declare STRING_PTR; initialize

! it with address of ARRAY[3]

You can use a STRING simple pointer for byte access to a word-addressed array. To

convert the word address to a byte address, use a left-shift operation ('<<' 1):

INT .word_array[0:39]; !Declare WORD_ARRAY

STRING .byte_ptr := @word_array[0] '<<' 1;

!Declare BYTE_PTR; initialize

! it with converted byte

! address of WORD_ARRAY

You can use an INT simple pointer for word access to a byte-addressed array. To

convert the byte address to a word address when you initialize the pointer, use a right-

shift operation ('>>' 1). (Only even byte addresses can be converted to correct word

addresses):

STRING .byte_array[0:4]; !Declare BYTE_ARRAY

INT .word_ptr := @byte_array[0] '>>' 1;

!Declare WORD_PTR; initialize

! it with converted word

! address of BYTE_ARRAY