[Open-graphics] Multipliers in oga1hq
Farhan Mohamed Ali
farhan at cmu.edu
Sat Sep 1 17:08:11 EDT 2007
Yes it would be quite useless to do a multiply by 0 on purpose. But i was
thinking about cases where you have no control over the inputs values? I
don't know. In any case, early termination was next on my list. However
it requires supporting an arbritrary shift distance which will be on the
critical path and maybe require quite a bit of hardware. We'll see how it
On Fri, August 31, 2007 10:42 pm, Paul Brook said:
>> The other question is, is this even beneficial? I seem to recall that
>> zeros occur quite commonly. Even in the MIPS ISA, r0 is just a
>> hardwired zero because of this if i remember right... so that is my
>> justification for doing this.
> I'd expect multiplication by zero to be relatively rare. One of the
> advantages of a zero register is that some unary operations can be
> implemented as a binary operation with a zero operand. e.g. x = -y can
> be implemented as x = 0 - y without requiring an extra instruction.
> Early termination when the high bits are zero (ie. small values) would
> be more useful. I've no idea how hard that is to achieve though.
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