> 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