pTAL Conversion Guide

Data Allocation

pTAL Conversion Guide—527302-002

5-5

Volatile Data

In pTAL, a data item can be declared with the VOLATILE attribute, which means that:

•

Every reference to the data item accesses its value from memory, not from a

•

The compiler does not rewrite code such that references to the data item could

lose the meaning you intend (for example, by moving expressions or statements

outside of loops, as in Example 5-2 on page 5-6)

?REFALIGNED(2)

INT(32) .ap1; ! References to these pointers

INT(32) .ap2; ! generate conservative code

INT(32) .ap3; ! because of REFALIGNED(2)

INT(32) .ap4; ! directive

?REFALIGNED(8)

INT(32) .ap11; ! These pointers do not cause

INT(32) .ap21 REFALIGNED(2); ! exceptions because the

INT(32) .ap31; ! pointers that are unaligned

INT(32) .ap41 REFALIGNED(2); ! specify REFALIGNED(2) clause

PROC p;

BEGIN

@p1 := @ap1 := @ap11 := @str[0]; ! Points to "ABCD"

@p2 := @ap2 := @ap21 := @str[2]; ! Points to "CDEF"

@p3 := @ap3 := @ap31 := @str[4]; ! Points to "EFGH"

@p4 := @ap4 := @ap41 := @str[6]; ! Points to "GHIJ"

i1 := p1; ! Uses fast code - access OK

i2 := ap1; ! Uses conservative code

i3 := ap11; ! Uses fast code - access OK

i4 := p2; ! Uses fast code - causes exception

i5 := ap2; ! Uses conservative code

i6 := ap21; ! Uses conservative code

i7 := p3; ! Uses fast code - access OK

i8 := ap3; ! Uses conservative code

i9 := ap31; ! Uses fast code - access OK

i10 := p4; ! Uses fast code - causes exception

i11 := ap4; ! Uses conservative code

i12 := ap41; ! Uses conservative code

END;

Example 5-1. Reference Alignment (page2of2)