Local Symbol Names

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Local symbols help compilers and programmers use names temporarily. They create symbols which are guaranteed to be unique over the entire scope of the input source code and which can be referred to by a simple notation. To define a local symbol, write a label of the form N: (where N represents any positive integer). To refer to the most recent previous definition of that symbol write Nb, using the same number as when you defined the label. To refer to the next definition of a local label, write Nf - The b stands for "backwards" and the f stands for "forwards".

There is no restriction on how you can use these labels, and you can reuse them as well. So it is possible to repeatedly define the same local label (using the same number N), although you can only refer to the most recently defined local label of that number (for a backwards reference) or the next 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:        jra 1f
2:        jra 1b
1:        jra 2f
2:        jra 1b
Which is the equivalent of:
label_1:  jra label_3
label_2:  jra label_1
label_3:  jra label_4
label_4:  jra label_3
Local symbol names are only a notational device. They are immediately transformed into more conventional 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, as retains these symbols in the object file. If you also instruct ld to retain these symbols, you may use them in debugging.

N
This is the number that was used in the local label definition. So if the label is written 55:, the number is 55.

\002
This unusual character is included so you do not accidentally invent a symbol of the same name.

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.