Jay Fox wrote:
> =?ISO-8859-1?Q?=22J=E9r=F4me_M=2E_Berger=22?= <jeberger@f
ree.fr> wrote:
>> Jay Fox wrote:
>>> I think LFSR generators would be far more common if chip-makers inclu
de
>> d a
>>> multiplicative equivalent of the XOR operator. In fact, were it not f
or
>>  this
>>> lack of xor-multiplication, LFSR's would be my favorite, as you could
 m
>> ake a
>>> LFSR equivalent of a MWC generator, with very little effort.
>>>
>>  Uh, what would this xor-multiplication do? If you see "xor" as a
>> bitwise addition, then the bitwise multiplication is done with the
>> "and" operator, which all modern CPUs have (and in fact this analogy
>> is even better than the xor-addition since bitwise multiplication
>> does not have trouble with carry and therefore never overflows).
>>
>>   Jerome
>> --
>> mailto:jeb### [at] freefr
>> http://jeberger.free.fr
>> Jabber: jeb### [at] jabberfr
> 
> I think you misunderstood what I meant by multiplication. I'm not talki
ng about
> "multiplying" 32 pairs of bits, one at a time. I'm talking about multip
lying a
> pair of 32-bit strings (or 16- or 8-bit, as the case might be).
> 
> Mutliplication:
> 
>   10010110
> x 10110011
> ----------
> 
> Can be rewritten as
> 
>          10010110  1
>         10010110   1
>               0    0
>              0     0
>      10010110      1
>     10010110       1
>           0        0
> + 10010110         1
> -----------------
> 
> The plus-sign is ordinary addition WITH CARRY for the field of integers
, or xor
> (which is addition WITHOUT CARRY) for the field of polynomials mod 2.
> 
	Okay, I see what you mean now. Although it seems that this kind of 
operation is pretty domain-specific which might explain why nobody 
has gotten around to integrating it into a general purpose processor...

		Jerome
-- 
mailto:jeb### [at] freefr
http://jeberger.free.fr
Jabber: jeb### [at] jabberfr

Post a reply to this message

Attachments:
Download 'us-ascii' (1 KB)