Example 1. Local Labels of the Form $n

This is an example of code that declares and uses a local label legally:

$1:
      ADDB  AL, #-7
      B     $1, GEQ

      .newblock	          ; undefine $1 to use it again.

$1    MOV   T, AL
      MPYB  ACC, T, #7
      CMP   AL, #1000
      B	    $1, LT

The following code uses a local label illegally:

$1:
      ADDB  AL, #-7
      B     $1, GEQ

$1    MOV   T, AL         ; WRONG - $1 is multiply defined.
      MPYB  ACC, T, #7
      CMP   AL, #1000
      B     $1, LT

The $1 label is not undefined before being reused by the second branch instruction. Therefore, $1 is redefined, which is illegal.

Local labels are especially useful in macros. If a macro contains a normal label and is called more than once, the assembler issues a multiple-definition error. If you use a local label and .newblock within a macro, however, the local label is used and reset each time the macro is expanded.

Up to ten local labels of the $n form can be in effect at one time. Local labels of the form name? are not limited. After you undefine a local label, you can define it and use it again. Local labels do not appear in the object code symbol table.