RE: computer-go: Sharing Go modules

[David Fotland <fotland@xxxxxxxxxxxxxxx>]

It's true that modern compiles can usually avoid the multiply.  For example if
you are iterating over a row in a loop, the compiler will only multiply once,
to get an index, then just add to the index as the loop advances.  But it won't
avoid all of the multiplies.

When I use one dimensional arrays, I never multiply in the go code.  The 
only multiply
is in the GUI, when the user selects a point.  All parameters and 
references inside
the go engine use a point index rather than an (x,y) pair.

David

At 10:47 PM 5/16/2001 -0700, you wrote:
> A one dimensional array doesn't avoid the multiply. You are doing the
> multiply yourself to convert x,y to index. I think modern day optimized
> compiler is more efficient than calculating the address yourself.
>
> Man Lung Li
>
> > -----Original Message-----
> > From: David Fotland [mailto:fotland@xxxxxxxxxxxxxxxxx]
> > Sent: Wednesday, May 16, 2001 7:20 PM
> > To: computer-go@xxxxxxxxxxxxxxxxx
> > Subject: RE: computer-go: Sharing Go modules
> >
> >
> > At 03:37 PM 5/16/2001 -0700, you wrote:
> > >Could you explain why a 2D array can cause a performance problem?
> >
> >
> > Take a look at the assembler output with a debugger.  To get
> > the memory address for a 2d 19x19 array, there is a multiply
> > by 19.  A one dimensional array avoids the multiply.  If the
> > computer has index addressing mode, a single instruction can
> > get the array value.
> >
> > David
> >
> >
> > >Thanks.
> > >
> > >-- Mousheng Xu
> > >
> > >-----Original Message-----
> > >From: Anders Kierulf [mailto:anders@xxxxxxxxxxxxxxxxx]
> > >Sent: Wednesday, May 16, 2001 8:33 AM
> > >To: computer-go@xxxxxxxxxxxxxxxxx
> > >Subject: RE: computer-go: Sharing Go modules
> > >
> > >
> > > > The coordinate coding method that I use is X,Y converts
> > to X+Y*20.
> > > > The arrays are all 421 long where all te points at 0,Y and X,0
> > > > contain special values to make it easy to detect the edge of the
> > > > board. This is a
> > >convenient
> > > > coding since it's still fairly easy to see which coordinates they
> > >represent
> > > > (for example: 63 is 3,3 and 356 is 16,17). However I do
> > realise that
> > > > every Go programmmer has their own idea of how this
> > should be done
> > > > and that there's little chance that I can convince
> > everyone in the
> > > > world to use
> > >this
> > > > scheme (that would be nice though <grin>) instead of
> > using separate
> > > > X and
> > >Y
> > > > coordinates.
> > >
> > >This is a good scheme. It's the same scheme SmartGo uses, so
> > at least
> > >two Go programs have independently reached exactly the same
> > solution.
> > >Please go ahead and convince the rest of the world. :-)
> > >
> > >Anders Kierulf
> > >www.smartgo.com
> > >
> > >
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> > David Fotland
> >
> >
David Fotland