Re: Guid question

From: Jon Shemitz (jon_at_midnightbeach.com)
Date: 03/15/05 

Date: Tue, 15 Mar 2005 08:45:36 -0800

Mike Margerum wrote:
 
> I am using guids (strings) as id's for my objects in a system i'm
> building. They work great but they are very large in string form (38
> bytes). Would it be a crazy idea to use the CRC of a guid string
> instead? that would be 4 bytes. That would still be pretty unique right?

I agree with those who say just use the full 16-byte binary Guid.

But, I recently had to write a hash routine for a Guid, and found that
multiplying each byte together (turning 0's into 1's) made a pretty
decent hash. I didn't do any mathematical analysis - but I did do a
NUnit test where I'd create a new Guid, hash it, and then create and
hash 100,000 or so other Guids without a collision.

Pretty simple to code - something like

  int Accumulator = 1;
  foreach (byte B in ThisGuid.ToByteArray())
    Accumulator = unchecked (Accumulator * ((B != 0) ? B : 1));

- which is probably a bit faster than a CRC. 

-- 
www.midnightbeach.com

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