Table of Contents
Advertisement
3.
An optional exponent: the letter E followed optionally
by an algebraic sign, followed by one or two decimal
digits.
4.
A binary scale specification: the letter B followed op-
tionally by an algebraic sign, followed by one or two
decimal digits that designate the terminal bit of the
integer portion of the constant (i.
e.,
the position of
the binary point in the number).
Bit position number-
ing begins at zero and refers to the leftmost bit of the
word or the doubleword in which the constant is to be
generated.
Items 3 and 4 may occur in any relative order.
When FX constants are used as explicit arguments in a
DA TA,n directive and 1 < n
5
4, t'hey are treated as a 32-
bit integerquantity(alignment on thebinarypointis relative
to this 32-bit field) and are generoted as such. In all other
uses, FX constants are treated as 16-bit integers, with binary
point alignment relative to this 16-bit field.
No checking is ever made for truncation from the right-
hand side of an FX constant.
Loss of significance on the
left-hand side or change of sign is flagged as an error.
Example:
Statement
DATA
FX
I
3.75B41
DATA,2
FX
I
3.75B41
DATA,3
FX ':3.75B41
SUB
=FX'-.OS32B1SE+41
DATA
FX''l BO'
GEN,S,S FX ' 3.75B41,1
Yloating-Point Short Constants
Generated Hexa ....
decimal Value
lEOO
1 EOO 0000
0000 1 EOO 0000
FF9S
(literal value)
(error)
(error)
A floating-point short constant consists of the following
components in order, enclosed by single quotation marks,
and preceded by the letters FS:
1.
An optional algebraic sign.
2.
d, d., d.d, or .d where d is a decimal digit string.
3.
An optional exponent: the letter E followed optionally
by an algebraic sign followed by one or two decimal
digits.
A floati ng-poi nt short constant requi res two memory words
for storage.
For this reason, a floating-point short constant
may appear only in the argument field of a DATA directive.
Example:
Constant
Hexadecimal Value
FS'l.
I
41100000
Floating-point short constants have a magnitude in the
range 5.398xlO-79 to 7.237xl0 75 (i.e., 16- 65 to 16 63 - 16 49 )
with the associated precision of 6 + significant digits. That
is, the sixth most significant digit is accurate, while the
seventh will sometimes be accurate, depending on the value
of the constant.
Floati ng-Poi nt Long Constants
A floating-point long constant consists of the followi ng com-
ponents in order, enclosed by single quotation marks and
preceded by the letters F L:
1.
An optional algebraic sign.
2.
d, d., d.d, or .d where d is a decimal digit stri ng.
3.
An optional exponent: the letter E followed optionally
by an algebraic sign followed by one or two decimal
digits.
A floating-point long constant requires three memory words
for storage.
For this reason a floating-point long constant
may appear only in the argument field of a DATA directive.
Example:
Constant
Hexadecimal
FL'-.9SEll
B19999990004
The magnitude of floating-point long constants is the same
as for floating-point short constants; however, floating-
point long constants have an associated precision of 10+
significant digits.
EXPRESSIONS
An expression is an assembly language element that repre-
sents a value.
It consists of a single term or a combination
of terms (multitermed) separated by arithmetic, logical, or
relational operators.
A si ngle-termed expression may be any valid symbol refer-
ence (previously defined, forward, common, or external),
a constant, or a literal.
(Symbol references and literals are
described later in this chapter.)
A multitermed expression may contain any valid symbol
reference (previously defined or forward) or a constant.
It
must not contain literals, forward procedure local refer-
ences, or external references. Appropriate error messages
are printed if any of these conditions is violated.
Operators and Expression Evaluation
A single-termed expression, such as 52 or $ or AB, takes on
the value of the term involved. A multitermed expression,
such as INDX+4 or ZD*S+XYZ, is reduced to a single value
by the assembler.
Language Elements
5
Advertisement
Table of Contents
