As we all no doubt know, the ISO C standard (and C++ as well, I think, though I'm more interested on the C side) allows three underlying representations of signed numbers:
- two's complement;
- ones' complement; and
Wikipedia's entry states that sign/magnitude is used on the IBM 7090 from the 60s, and that ones' complement is used by the PDP-1, CDC 160A and UNIVAC 1100, all of which date back to the 60s as well.
Are there any other implementations of C (or underlying hardware) with these alternative representations, that have come out a little more recently than fifty years ago (and what are they)?
It seems a little wasteful to keep something in a standard for machines no longer in existence.