Compilers and languages (Was: Help reading a 9 track tape

Chuck Guzis cclist at
Tue Aug 3 13:44:28 CDT 2021

On 8/3/21 9:46 AM, ben via cctalk wrote:

> Hardware makes software interesting, or is it the other way around?
> With C being developed on a PDP 11, you had no decimal operations,
> but IBM had PL/I that did. Every thing was binary floating point
> since then, until the latest standard of floating point for
> hardware and software came out. Decimal is BACK Now things are more
> confusing than ever with operating systems changing CPU's with the
> latest marketing gimmick.

You don't need decimal hardware to do decimal arithmetic. CDC 6000 COBOL
killed IBM S/360 COBOL, even though the latter had hardware decimal
features and the former did not--the big CDC iron was never really sold
as a COBOL cruncher, even though it did quite well at it.

Using numbers in their 6-bit display code representation (33->44 octal),
it's a simple matter to perform 10 digit decimal addition and
subtraction in just a few instructions.   I'll leave it as an exercise
to those who are curious (I'll give a hint that octal 25 25 25 25...
plays a part).

Also note that display "0' = 33 octal and display "9" = 44 octal, so
that nines' complement of a display number is the same as the ones'
complement, so subtraction follows quite naturally.

The CDC 6000 has only one addressing granularity--60 bit word.  There's
no CPU hardware for handling bytes (6 or 8 bit).  Yet character
manipulation isn't very difficult at all.

The wonders of RISC.  Do a few things, but do them quickly.


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