C history / was Re: newbie building a scratch-built computer

[Ethan Dicks]

On 8/2/07, Brent Hilpert <hilpert at cs.ubc.ca> wrote:
> > On 1 Aug 2007 at 20:56, dwight elvey wrote:
> > > C doesn't fit well onto any of the processors that I've seen lately.
> > > It is always sub-optimal.

C works pretty well on my PDP-11  ;-)  Of course, it's been long
pointed out that C is just PDP-11 assembly shorthand - having waded
through the guts of C-compiler output on a few architectures, I
completely agree that's how it started out.

C on a 68K is nice, too, but for those that know the PDP-11 and 68K
architecture, that's no surprise.  C on a VAX is also nice.

Can't say I've dig deeply enough on any processor architecture newer
than about 1978, so perhaps that merely reinforces your statement.

> Apropros of not much, but to ensure this is on-topic, I never hear B or BCPL
> mentioned, the ancestors of C, and even 'closer to the machine'. I'm not sure
> how many C programmers these days even know it has such ancestors.

Amiga programmers know about BCPL.  AmigaDOS, nee Tripos, is riddled
with "BPTR"s - take a regular pointer to anything, enforce long-word
alignment, and, as a consequence, observe that the bottom two bits are
always 00.  Now... since the pointers your compiler generates always
end in two zeros, right-shift your pointers twice before saving them
in a variable.  This has the intended benefit of allowing you to store
pointers to objects in a 256K (18-bit) environment in 16-bit
variables.  It has the unintended consequence of messing with the
heads of assembler and C programmers.  You have to remember to
double-left-shift BPTRs before dereferencing them, and to
double-right-shift them when you are done incrementing them and want
to store them for later use by a system call or whatever.  This
routinely leads to pointer bugs when writing AmigaDOS programs,
especially among the unwary.

So I've never programmed in B or BCPL, but I spent years dealing with
the downstream effects of them.  So did every Amiga C and assembler
programmer 20 years ago.

Other than the on Amiga, though, I suspect to most, B and BCPL are
footnotes in K&R.

-ethan