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-----Original Message-----

All these different multiplier organizations have one thing in common; they
use carry-save adders.
In fact a traditional (pipelined) shift-add multiplier can be written to use
carry-save adders.

Just browse the internet, or get a copy of Perhami's "Computer Arithmetic"
book.

Cheers,
Richard

> -----Original Message-----
> From: cores-bounces@o... [mailto:cores-bounces@o...] On
> Behalf Of Steven R. McQueen
> Sent: Friday, May 14, 2004 7:52 AM
> To: Discussion list about free open source IP cores
> Subject: [oc] Question on Modular Multipliers
> 
> I am the author of the Basic RSA project on Open Cores. It does what I
> originally intended it to do, but frankly, its performance is
> embarrassing. I have been trying to wade through papers on high radix
> modular multipliers, including Montgomery, and something does not seem
> right to me. If I understand correctly, the speed advantages in these
> systems come from pre-calculating the possible products (i.e. 1x1,
> 1x2,...4x3, 4x4 for radix 4) and adding those, instead of the
> traditional shift and add multiplication.
> 
> Unfortunately, it seems to me that this can only be effective for a
> non-modular multiplier, since massive adders and subtractors are still
> required to be chained together to get the correct modular result. What
> am I missing here?
> 
> Also, I have seen some papers on partial adders that claim to accelerate
> large multipliers (>512 bits) considerably. I can see how clock rates
> can be accelerated dramatically, but I cannot see how the throughput is
> improved. It seems to me that carries must still be propagated which
> would cancel most of the benefit of the faster clock.
> 
> I have developed a partitioned adder that doubles the speed of 1024-bit
> add operations at the cost of 4 times the circuitry, but this does not
> seem cost-effective to me, and it does not scale well. If anyone can
> point me to some nice, clear descriptions of high performance large
> number adders or multipliers, preferably with lots of examples, or can
> shed some light on the subject personally, I would greatly appreciate
> it.
> 
> Thank you!
> 
> Steve
> 
> --
> Steven R. McQueen <srmcqueen@m...>
> McQueen Technologies, Inc.
> 
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