18 bit CPU; was: Speed now & then

[Toby Thain]

On 2018-04-12 7:48 AM, Bill Gunshannon via cctalk wrote:
> 
> 
> On 04/12/2018 02:45 AM, Chuck Guzis via cctalk wrote:
>> On 04/11/2018 06:38 PM, Chuck Guzis via cctalk wrote:
>>> On 04/11/2018 02:48 PM, ben via cctalk wrote:
>>>
>>>> I have a nice 18 bit cpu here, with only a few hardware bugs.
>>>> Hmm would it work better if I change that around ideas.
>>>>
>>>> Care to point to a nice 18 bit version of unix or C.
>>>> BTW The cpu has a frame pointer S but no S++ --S operations
>>>> so pushing and popping wild data is not a option.
>>> Well, the Univac 1100/2200 series mainframes ran V7 Unix--and they're
>>> 36-bit machines, so probably not far from your 18-bitter--and they're
>>> ones' complement machines.
>>>
>>> Univac called it "SX1100", so you have a search term.
>> Remarkably, Unisys keeps a lot of old documentation around.  Here's the
>> reference manual for their "C" on th 1100:
>>
>> https://public.support.unisys.com/2200/docs/cp14.0/pdf/78310422-011.pdf
>>
>> Looks pretty much like standard C until you get into the minutiae, such
>> as "A character constant is 1 to 4 characters" ...

Apple also used this extension in their Mac C compilers.

>> (9 bit characters and 36 bit ints and 18 bit short ints).
>>
>> So, it should be pretty straightforward unless you assume that a char is
>> 8 bits, with a signed char having a range of +/-255.
>>
> 
> Signed 8 bits would be  -128 to +127.

Yes, but Chuck was describing the Univac, where char is a 9-bit type,
and a signed char is 1 sign bit and 8 magnitude bits, giving +/- 255.

--Toby

> 
> bill
>