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Path: utzoo!linus!decvax!borman
From: borman@decvax.UUCP (Dave Borman)
Newsgroups: net.lang
Subject: Re: Self-modifying code
Message-ID: <324@decvax.UUCP>
Date: Wed, 4-Jan-84 12:10:44 EST
Article-I.D.: decvax.324
Posted: Wed Jan  4 12:10:44 1984
Date-Received: Thu, 5-Jan-84 01:18:30 EST
References: <2157@fortune.UUCP>
Organization: DEC UNIX Engineering Group
Lines: 16

Several years ago (~1979/1980) at St. Olaf College (it's in Minnesota, stolaf
on the net) a plotting package was written in C, to run under V7 on a PDP
11/70. One question was how to allow the user to input functions to be plotted,
and how to evauluate them.  What was decided upon was to write a function
compiler, so that at run time the functions could be broken down into assembly
and then executed.  The machine instructions were put into an integer array,
and then the array was cast into a function pointer and called for each
point at which a value was needed.  The compiler handled all normal arithmetic
operations, plus summations, products, conditionals, constants, and references
to other functions, both user defined and from an internal library. The only
drawback to this scheme is that since the code is being generated in data
space, in order to execute it you can't have compiled the program split I/D.

The author of this function compiler is Steve Tarr.

			-Dave Borman, decvax!borman