two's complement, was Re: Now OT

Chuck Guzis cclist at
Thu Jun 23 12:13:12 CDT 2016

On 06/23/2016 09:09 AM, Paul Koning wrote:

> The CDC 6000 did that in part.  It has full 60 bit integer
> add/subtract, but multiply and divide are done using the floating
> point operations so they work only for numbers up to 47 bits.

The CYBER 200/STAR 100 limited integers to 48 (of 64) or 24 (of 32)
bits.  The same held for addresses (this was a bit-addressable machine).
 The upper 16 bits of a 64 bit word is reserved for exponents and lengths.

Integer instructions were available for adding and subtracting the lower
48 bits without affecting the upper 16.  Boolean operations, of course,
worked on all bits of a word.

If the user needed extended-precision binary (or decimal) arithmetic, he
could turn to the string instructions which provided 4-banger math on
integers up to 65KB in length.


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