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On Wed, Nov 17, 2010 at 13:38, Andrea D'Amore <> wrote:
> On Wed, Nov 17, 2010 at 6:51 PM, Leo Razoumov <> wrote:
>> In order to map XOR into regular multiplication FALSE is 1 and TRUE is -1.
>> This is counterintuitive but has been used with great success in DSPs and ASICs.
> Hello,
> could you give me any further info about this?
> I'm approaching Hennessy-Patterson fourth edition right now and I
> guess what you wrote is related to high performance computing.
>> --Leo--
> Regards
> --
> Andrea

Hi Andrea,
my examples come from digital communications and electrical
engineering. In radio communications when you are sending a binary
string you need to somehow map 0s and 1s into some electro-magnetic
signals. This process is called modulation. The simplest digital
modulation is BPSK (Binary Phase Shift Keying) where you map 0,1 into
+1,-1 voltages. Naively you might think that
both mappings 0->+1, 1->-1 and 0->-1,1->1 are equivalent and just a
convention. But when you need some operations on them (like Hadamard
transform, etc) the "counterintuitive map" of 0->+1, 1->-1 happens to
save you quite a few CPU cycles. Little tricks of the trade:-)