SYMBOL TABLE n v t 113 DD Dis the value of the third 1 2 31 U 31 is a pointer to the ADD instruction An advantage of this feature is that the local labels are easy to identify as such, since their names start with a digit. Most assemblers require regular label names to start with a letter. In modern assemblers, local labels sometimes use a syntax different from the one shown here. The LC as a local symbol Virtually all assemblers allow a notation such as ‘BPL *+6 where stands for the current value of the LC. The operand in this case is located at a point 6 locations following the BPL instruction. The LC symbol can be part of any address expression and is, of course, relocatable. Thus A is valid if A is absolute, while A is always okay (and is absolute if A is relative, relative if A is absolute).This feature is easy to implement. The address expression involving the is calculated, using the current value of the LC, and the value is used to assemble the instruction, or execute the directive, on the current source line. Nothing is stored in the symbol table. Some assemblers use the asterisk for multiplication, and may designate the period or the for the LC symbol. On the PDP-11 the notation Xis used to increment the LC by and thus to reserve eight ocations (compare this to the DS directive. EXERCISE What is the meaning of JMP *,JMP *-*?
