36
Chapter 6. Symbols
definition of a specific local label for a forward reference. It is also worth noting that the first 10 local
labels (
0:
. . .
9:
) are implemented in a slightly more efficient manner than the others.
Here is an example:
1:
branch 1f
2:
branch 1b
1:
branch 2f
2:
branch 1b
Which is the equivalent of:
label_1:
branch label_3
label_2:
branch label_1
label_3:
branch label_4
label_4:
branch label_3
Local symbol names are only a notational device. They are immediately transformed into more con 
ventional symbol names before the assembler uses them. The symbol names stored in the symbol
table, appearing in error messages and optionally emitted to the object file. The names are constructed
using these parts:
L
All local labels begin with
L
. Normally both
as
and
ld
forget symbols that start with
L
. These
labels are used for symbols you are never intended to see. If you use the
 L
option then
as
retains
these symbols in the object file. If you also instruct
ld
to retain these symbols, you may use them
in debugging.
number
This is the number that was used in the local label definition. So if the label is written
55:
then
the number is
55
.
C B
This unusual character is included so you do not accidentally invent a symbol of the same name.
The character has ASCII value of
\002
(control B).
ordinal number
This is a serial number to keep the labels distinct. The first definition of
0:
gets the number
1
.
The 15th definition of
0:
gets the number
15
, and so on. Likewise the first definition of
1:
gets
the number
1
and its 15th defintion gets
15
as well.
So for example, the first
1:
is named
L1C B1
, the 44th
3:
is named
L3C B44
.
6.3.2. Dollar Local Labels
as
also supports an even more local form of local labels called dollar labels. These labels go out of
scope (ie they become undefined) as soon as a non local label is defined. Thus they remain valid for
only a small region of the input source code. Normal local labels, by contrast, remain in scope for the
entire file, or until they are redefined by another occurrence of the same local label.
Dollar labels are defined in exactly the same way as ordinary local labels, except that instead of being
terminated by a colon, they are terminated by a dollar sign. eg
55$
.






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