7 Mar
2011
7 Mar
'11
4:51 p.m.
It was thus said that the Great Jules Richardson once stated:
Chuck Guzis wrote:
I'm looking at _TRS-80 Color Computer Assembly Language Programming_ by
William Barden, Jr., and he states:
Although it's possible to do [signed multiply] with special
multiplies ... the easiest way is to first convert the operands to
absolute values, do the multiply ... and then change back the result
to the proper sign.
(Chater 17, pg 170)
For multiplication,
+X * +Y = +Z
-X * +Y = -Z
+X * -Y = -Z
-X * -Y = +Z
Looks like the sign of the result is the exclusive or of the sign bits
(but beware of overflow)
-spc
There were math co-processor boards (AM9511,
AM9512, for example) for
S100 systems. ISTR that there was even a TRW bipolar (16x16? Huge
chip that ran hot as a pistol) for the S100 bus.
I suppose if it appears transparent to the user (machine executes
instruction xx, doesn't know what to do with it, and throws it at the
copro) then it's a valid solution. I think I'm more interested in systems
that came with support as standard rather than as an optional cost extra,
though.
The Moto 6809 had an 8x8 multiplier.
Yes, that seems to be the 'famous' one that gets mentioned everywhere. It
seems it was of the shift-add variety. Anyone recall if it would work with
signed integers? (I'm just trying to work out how the math works for signed
multiplies at the moment)