Path: utzoo!utgpu!attcan!uunet!lll-winken!lll-tis!ames!nrl-cmf!cmcl2!rutgers!bellcore!faline!thumper!ulysses!andante!alice!dmr
From: dmr@alice.UUCP
Newsgroups: comp.misc
Subject: Re: Basics of Program Design
Message-ID: <8072@alice.UUCP>
Date: 28 Jul 88 04:53:50 GMT
Organization: AT&T Bell Laboratories, Murray Hill NJ
Lines: 29

I suppose I should save this article, since the subject seems
to come up every year.

C was developed on the PDP-11; most of it aside from the type
structure and associated syntax came from B, which was developed on
the PDP-7.  B already had the ++ and -- operators (and the associated
idioms like *p++).  The first B compiler produced interpreted
(threaded) code.  Doubtless the invention of ++ and -- (due to
Thompson) was suggested by the auto-increment cells of the PDP-7, or
perhaps the one such cell on the PDP-8, or perhaps some of the more
recondite indirection modes on the GE 635/645, or the
count-increment-refill mechanism of the Stretch.  In any event, neither
B nor the first C compiler generated -7 or -11 instructions that used
autoincrement.

C was less influenced by the PDP-11 than most people think.  Certainly
the addition of types was motivated by the desire to take advantage
of byte addressing and the (future) existence of floating point
(indeed, C compiled 11/45 floating point instructions before
the delivery of any 11/45s; it was an annoyance when DEC changed
its mind about what opcodes to use.)

Discounting general things like that, the only strong PDP-11isms I can
think of in C are the signed characters and about 50% of the
justification for the widening rules for floats.  (The other 50% is
simplification of the language rules and libraries).

	Dennis Ritchie
	research!dmr
	dmr@research.att.com