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2. EXTENDED SYMBOL LANGUAGE ELEMENTS AND SYNTAX
LANGUAGE ELEMENTS
Input to the assembler consists of a sequence of characters
that are combined to form assembly language elements. These
language elements, which include symbols, constants, ex-
pressions, and literals, comprise pmgram statements which
in turn comprise a source program.
CHARACTERS
The Extended Symbol character set is shown in Figure
1.
Alphabetic:
A through Z, and
$f!-Z" #,
L-J
(break char-
acter pri nts as
01
underscore")
Numeric:
Special
Characters:
(: is reserved alphClbetic character)
o
through 9
Blank
+
Add (or posi ti ve va I ue)
Subtract (or negative value)
*
/
&
I
II
Multiply, indirect addressing prefix,
source regish::r inversion designator,
or comments line i ndi cator
Divide
Decimal point
Comma
Left parenthesi s
Right parenthesis
Constant del imiter (single quotation
mark)
Logical AND
Logical OR (vertical slash)
Logical exclllsiveOR (vertical slashes)
-,
Logical NOT or complement
<
>
Less than
Greater than
Equa I or introduces a litera I
<=
Less than or equal
>:=;
Greater than or equal
Continuation code
**
Binary shift
TAB
Equivalent to blank; used to tabulate
keyboard printer output
Figure
1.
Extended Symbol Character Set
The colon (:) is an a Iphabetic character reserved for use by
standard Xerox software.
It is included in the names of
Moni tor routines (M :POP) and various mathematica I sub-
routines (L:ATAN) to avoid any potential conflict with user
symbols.
SYMBOLS
Characters are combi ned to form symbols.
Symbols provide
programmers wi th a conveni ent method of i denti fyi ng pro-
gram elements so they can be referred to by other elements.
Symbols must conform to the followi ng rules:
1.
Symbols should consist of
1
to
8
alphanumeric charac-
ters: A-Z,
$,
Jl~, #, :,
L-J,
0-9,
of which at least one
must be alphabetic.
No special characters or blanks
may appear in a symbol.
Only the first eight charac-
ters will be used by the assembler to identify the pro-
gram element represented by the symbol. Anyremaining
characters are ignored in processing the symbol and (if
requested) a warning error is output on the listing.
2.
The characters $ and
$$
may be used in the argument
field of a statement to represent the current value of
the execution and load location counters, respectively
(see Chapter
5);
these characters must not be used as
symbols in the label field (see "Syntax" later in this
chapter).
The following symbols are valid:
ARRAY
R1
INTRATE
BASE
7TEMP
#CHAR
$PAYROLL
$
(execution location counter)
The following symbols are also valid, but only the llnder-
I ined portion is considered by the assembler and (if requested)
a warning error is noted.
~A
TE01)NCREASE
Q!JJE~IV ~LUE
ABINVERSE
- - - - -
The following symbols are invalid:
BASE PAY
Blanks may not appear in symbols.
Special characters
(~-::)
are not permitted
in symbols.
Extended Symbol Language Elements and Syntax
3
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