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From: dhc@exodus.UUCP (David H. Copp)
Newsgroups: net.wanted
Subject: Re: Simple Cross Assemblers
Message-ID: <155@exodus.UUCP>
Date: Thu, 3-May-84 09:28:38 EDT
Article-I.D.: exodus.155
Posted: Thu May  3 09:28:38 1984
Date-Received: Fri, 4-May-84 02:40:30 EDT
References: <1599@burdvax.UUCP>
Organization: Bell Communications Research
Lines: 33

If it really is a small job, for a small machine--writing
your own assembler might be easier than you think.

I once saw an assembler that consisted of little more than
two tables, a reserved word table and a symbol table.

The reserved word table contained the mnemonic names for
the opcodes and the registers, etc..  Each entry
consisted of the pair

	<word>	<bit pattern>

where the bit pattern was one machine word wide, and consisted
of the corresponding op-code, etc., in the right place in the word,
and zeros elsewhere.

The symbol table contained (as I recall) only address symbols
and their definitions (numerical addresses).  This was a teeny
bit complicated--a hash table--but only a teeny bit.
Again, each definition was one machine word wide, with the
address in the appropriate field and zeros elsewhere.

The assembler only did two basic things; make entries in the
address table (whenever a label was encountered), and --

	TA DA ...

generate code, by Boolean-ORing the definitions for all tokens
(except labels and comments) on one line of assembler input!

It implements a primitive assembly language, but it works.
-- 
				David H. Copp