Re: Three Address Code

Dan Cohen <>
15 Sep 2000 01:37:03 -0400

          From comp.compilers

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Three Address Code (2000-09-11)
Re: Three Address Code (Sid Ahmed Ali TOUATI) (2000-09-13)
Re: Three Address Code (Travers Naran) (2000-09-13)
Re: Three Address Code (Travers Naran) (2000-09-15)
Re: Three Address Code (Dan Cohen) (2000-09-15)
Re: Three Address Code (Rainer Leupers) (2000-09-17)
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From: Dan Cohen <>
Newsgroups: comp.compilers
Date: 15 Sep 2000 01:37:03 -0400
Organization: Compilers Central
References: 00-09-088 00-09-094
Keywords: code, architecture

Travers Naran wrote:
> <> wrote in message
> > I would like to know if Three Address Code can be implemented in some
> > way other then quadruple or triples.
> I don't get it: isn't three address code inherently a n-tuple of
> addresses? Finding another implementation is looking for something
> other than three address code, isn't it? I am curious about this
> because I've only ever used n-tuples (quadruple or triples) and I too
> would be interested if there was another way.

My first computer was a microprogrammed machine. The micro instructions
allowed me to create a new programming language. I was pretty new to
programming, so I chose a 3-address scheme, like this:
op source1 source2 destination
and the operands were all memory (RAM) addresses.

Here's an example program to convert to upper case: (the dashes are
place holders, my input was formatted)

in tty0 - buffer ! input a character from console
comp buffer 'a' - ! set flags by internal subtract
jump neg - dont ! buffer < 'a', not lower case
comp buffer 'z' - ! set flags by internal subtract
jump pos - dont ! buffer > 'z', not lower case
sub 'a' buffer buffer ! lower - 'a'
add 'A' buffer buffer ! + 'A' gives UPPER

It seemed like a good idea at the time. But you'll notice that every
instruction coded in this routine has an unused field, or else a
duplicate field. Actually, in use, I had a lot of instructions with 2
fields unused, too.

Well, my assembler program worked, and I am proud of it. But I'll never
do it that way again.

Today, I sometimes to 803876, but actually I prefer 65c02 or 68000.

  -- Dan Cohen in Calgary

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