> On Aug 22, 2015, at 10:31 PM, Chuck Guzis <ccl...@sydex.com> wrote:
>
> On 08/22/2015 06:26 PM, Paul Koning wrote:
> than the usual rule).
>>>
>>> I recall the "integer multiply" feature (i.e. optional) available
>>> on the 6000. IXi Xj*Xk, but it didn't provide any more precision
>>> than the usual unnormalized double-precision multiply DXi Xj*Xk,
>>> but saved some time spent fiddling with exponent fields.
>>
>> ??? Never heard of any such thing. IXi Xj*Xk is a defined opcode,
>> but it's simply a synonym for Dxi Xj*Xk.
>
> Well, we were always the guinea pig for QSEs in SSD. It's not described in
> the Cyber 70 docs, but we had Cybers fitted with the option. It did make its
> way into the 170s however:
>
> In 60456100A, re: the 42 instruction (page 4-24, second column):
>
> "This instruction is used in multiple-precision floating-point calculations.
> This instruction also provides for integer multiplication capabilities where
> both operands have an exponent value of plus or minus zero and neither
> coefficient has been normalized. The integer result sent to Xi is *48 bits
> with a 60-bit sign extension* (emphasis mine)."
Ok, but that is simply the standard 6000 series double multiply. That's not an
optional feature; the behavior you describe is how it always works and why
IXX*X is a synonym for DXX*X. All that's going on here is that the exponent
field remains zero, so it acts as an extended sign field.
paul
