Re: Re: Adler-32 Checksum

Johnson Walter-CWJ002 wrote:
> Is there any property that makes the Internet Checksum better at detecting a handlespace inconsistency as compared to a simple XOR of the byte block data which is composed of the pool handle zero padded to a 32 bit work boundary and the 32 bit PE Id?
> 
> Wondering since the Internet checksum will be more computationally expensive.

I'm not sure what your concern is here.  The Internet checksum
is just the ones's complement of (one's complement sum + carry).
That's two additional steps over a simple XOR sum.

The checksum has the property that it is endian independent (of
course the checksum is in the same endian as the CPU though).

--peter

> Thanks
> Walter 
> 
> -----Original Message-----
> From: [email protected] [mailto:[email protected]] On Behalf Of Peter Lei
> Sent: Wednesday, June 29, 2005 2:29 PM
> To: Michael Tuexen
> Cc: Xie Qiaobing-QXIE1; Thomas Dreibholz; [email protected]; [email protected]; Silverton Aron-C1710C
> Subject: Re: [Rserpool] Re: Adler-32 Checksum
> 
> Michael Tuexen wrote:
> 
>>32 bits are longer and therefore better, but the 16 bit algorithm is
>>- already described in RFC 1071
>>- supported on NICs in hardware.
>>
>>Since it might be difficult to use a NIC to do the computation,
>>because RSerPool normally will be implemented in userland,
>>I would also vote for the 32 bit version and describe the
>>algorithm explicitly in the ENRP ID.
>>
>>If others agree I can put some text in the ID.
> 
> 
> I agree with using 32-bit checksum.
> 
> --peter
> 
> 
>>Best regards
>>Michael
>>
>>On Jun 28, 2005, at 15:59 Uhr, Thomas Dreibholz wrote:
>>
>>On Tuesday 28 June 2005 15:53, Michael Tuexen wrote:
>>
>>
>>>>>>I think, the Internet checksum algorithm (may be with keeping the
>>>>>>full 32 bits
>>>>>>instead of truncating to 16 bits) should already be sufficient for
>>>>>>the audit
>>>>>>purpose. Using this checksum algorithm, we also get order-
>>>>>>invariancy and do
>>>>>>not need to force a specific ordering of the handlespace within a
>>>>>>management
>>>>>>component. It is furthermore very simple and fast (only + and ~
>>>>>>operations
>>>>>>are needed, no *, / or %).
>>>>>
>>>>>
>>>>>So the Internet checksum is the way to go... I have no particular
>>>>>preference
>>>>>in 16 bit or 32 bit.
>>
>>
>>I would prefer 32 bits. The checksum parameter pads the sum to 32
>>bits  of
>>space anyway - so why not use the full 32 bits, making the
>>probability  that
>>two states of the handlespace map to the same checksum value much 
>>smaller?
>>
>>
>>Best regards
>>--
>>=======================================================================
>> Dipl.-Inform. Thomas Dreibholz
>>
>> University of Essen,                            Room ES210
>> Inst. for Experimental Mathematics              Ellernstraße 29
>> Computer Networking Technology Group            D-45326 Essen/Germany
>>- 
>>-----------------------------------------------------------------------
>> E-Mail:     [email protected]
>> Homepage:   http://www.exp-math.uni-essen.de/~dreibh
>>=======================================================================
> 
> 
>