Intel XENIX 286 Programmers Guide (86) - Tenox.tc

XENIX Programming as: Assembler
A numeric label consists of a string of the digits 0 to 9 followed by a dollar sign ($)
followed by a colon (:). Such a label serves to define local symbols of the form
n$
where n is the digit of the label. The scope of the nu meric label is the labeled block in
which it appears. As an example, the label "9$" is defined only between the labels
Iabell and label2:
label 1:
9$:
label2:
.byte 0
.word a
As in the case of name labels, a numeric label assigns the current value and type of dot
to the symbol.
Null Statements
A null statement is an empty statement (which may, however, have labels and a
comment). A null statement is ignored by the assembler. Common examples of null
statements are empty lines or comment lines.
Expression Statements
An expression statement consists of an arithmetic expression not beginning with a
keyword. The assembler computes its value and places it in the output stream, together
with the appropriate relocation bits.
Assignment Statements
An assignment statement consists of an identifier, an equal sign (=), and an expression.
The value and type of the expression are assigned to the identifier. It is not required
that the type or value be the same in pass 2 as in pass 1, nor is it an error to redefine
any sy mbol by assignment.
Any external attribute of an expression is lost across an assignment. Thus you cannot
declare a global sy mbol by assigning to it. Nor can you define a symbol to be offset
from a nonlocally-defined global symbol.
As mentioned, you can assign the location counter. It is required, however, that the
type of the expression assigned be of the same type as dot, and an assign ment cannot
decrease the value of dot. In practice, the most common assignment to dot has the
form
. = . +n
for some number n; this has the effect of generating n null bytes.
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