11 May
2005
11 May
'05
11:05 a.m.
Subject: Re: Infocom on PDP-11
From: Eric J Korpela <korpela at gmail.com>
Date: Tue, 10 May 2005 15:50:02 -0700
To: "General Discussion: On-Topic Posts Only" <cctech at
classiccmp.org>
The C data types only have minimum sizes. Actual sizes are up to the
implementation.
The resulting C data types for a PDP-8 would be 12-bit char, 24 bit
short and int, 36 bit long. As long as limits.h contains the correct
values and the sizeof() operator correctly returns 1, 2 and 3 for the
What about byte as in 6bits. Thats a valid item for PDP-8 as one
intruction BSW swaps accumulator halfs. Also much of the character
IO was 6bit.
Don't ask me to write the floating point library,
though...
Don't have to as there was a good asm one supplied with the machine. ;)
Allison
11 May
11 May
11:33 a.m.
From: "Allison" <ajp166 at bellatlantic.net>
Afraid those would have to be user data types, as the C standards require 8
or more bits for "char".
I think they would be useful (even necessary) additions to a "C-like" system
programming language for the PDP-8, though.
Vince
The C data
types only have minimum sizes. Actual sizes are up to the
implementation.
The resulting C data types for a PDP-8 would be 12-bit char, 24 bit
short and int, 36 bit long. As long as limits.h contains the correct
values and the sizeof() operator correctly returns 1, 2 and 3 for the
What about byte as in 6bits. Thats a valid item for PDP-8 as one
intruction BSW swaps accumulator halfs. Also much of the character
IO was 6bit. 
12 May
12 May
12:48 p.m.
What about byte as in 6bits. Thats a valid item for
PDP-8 as one
intruction BSW swaps accumulator halfs. Also much of the character
IO was 6bit.
Unfortunately in C, a char has to at least be able to hold 255 unique
values (-127 to 127 if char is signed). There's also the problem of
pointer math since pointers to different chars have to have different
values. It's surmountable, but it increases the size of a pointer.
The way around this is to define a packed_char type for interfacing
with 6bit io routines...
typedef union tag_packed_char {
struct tag_chars { unsigned int a:6,b:6,c:6,d:6; };
unsigned int u;
} packed_char;
Eric
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