pTAL Conversion Guide

Structures
pTAL Conversion Guide—527302-002
11-11
Definition Structure Syntax
field-alignment
FIELDALIGN
specifies how you want the compiler to align the base of the structure and
fields in the structure. The offsets of fields in a structure are aligned relative to
the base of the structure.
In pTAL:
•
If a definition substructure does not specify a FIELDALIGN clause, the
contained substructure’s field alignment is the field alignment of its
encompassing structure or substructure.
•
If you do not specify a FIELDALIGN clause on a structure declaration,
pTAL uses the current value of the FIELDALIGN compiler directive. The
default value of the FIELDALIGN directive is AUTO.
•
If you specify a FIELDALIGN (NODEFAULT) compiler directive, you must
specify a FIELDALIGN clause on every definition structure and template
structure.
SHARED2
specifies that the base of the structure and each field in the structure must
begin at an even-byte address except STRING fields, which can begin at any
byte address, and UNSIGNED fields for which the rules are described later in
this section.
pTAL allocates the same offsets and widths for the fields of a structure
declared with FIELDALIGN(SHARED2) as TAL does for the same structure.
SHARED8
specifies that the offset of each field in the structure from the base of the
structure must begin at an address that is an integral multiple of the width of
the field. The structure must begin at an address that is an integral multiple of
the width of the widest field in the structure; therefore:
•
A one-byte field (STRING) can begin at any byte address.
•
The byte offset of a two-byte field (INT, UNSIGNED(1-16)) must be an
even number, except that contiguous UNSIGNED fields can be packed.
FIELDALIGN
( SHARED2
SHARED8
AUTO
PLATFORM
)
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