Re: Stealing a Great Idea from the 6600

On Sat, 20 Apr 2024 17:59:12 -0600, John Savard
<quadibloc@servername.invalid> wrote:

On Sat, 20 Apr 2024 22:03:21 +0000, mitchalsup@aol.com (MitchAlsup1)
wrote:

BGB wrote:

>

   Sign-extend signed values, zero-extend unsigned values.

>

Another mistake I mad in Mc 88100.

>
As that is a mistake the IBM 360 made, I make it too. But I make it
the way the 360 did: there are no signed and unsigned values, in the
sense of a Burroughs machine, there are just Load, Load Unsigned - and
Insert - instructions.

Since there was only one set of arithmetic instrucions, that meant
that when you wrote code to operate on unsigned values, you had to
remember that the normal names of the condition code values were
oriented around signed arithmetic.

So during unsigned arithmetic, "overflow" didn't _mean_ overflow.
Instead, carry was overflow.

John Savard