Table of Contents
Advertisement
Assembly Language Fundamentals
77
Unlike BASIC, there is no precedence among the operators. All are of equal precedence.
Where precedence is desired, parentheses must be used. So where BASIC requires -
2*16+3*8
to result in 56, the same expression in the assembly language results in 280 (assembly language
operators are evaluated from left to right). However, 56 would be the result if
it
were expressed
as-
(2*16) +(3*8)
An expression may be of any length and contain as many operators and parentheses as desired,
as long as the result can be evaluated and the parentheses are properly paired. All operators
are evaluated from left to right. Multiplication and division can only be used with elements that
are of type absolute.
External Symbols and Elements
There is an additional relocatable element, called "external". It behaves in almost all respects
as does any other relocatable element, except that only one external item may appear in an
expression. Also, the expressions containing -
relocatable - relocatable
are not allowed when one of the relocatable elements is external. Externals are defined as
symbols appearing in an EXT pseudo-instruction -
i:=~:>CT·
{symbol}
L
{symbol}
L ...
J J
These are entry points in another module or utility. "Entry points" are merely symbols in a
module which are listed in an ENT pseudO-instruction in that module -
FJ·rr·
{symbol}
L
{symbol}
L ... J J
If one module contains -
then that symbol would be available to another module which contains -
l::: ...
;:< ·T·· . . . . . . ,
!... .::'. :::::;
~:::
I
C:
·f·
t.
I
- Quick Links:
- Program Creation
Hide quick links:
Advertisement
Table of Contents
