This is why you should not use numeric fields as search fields in IMAGE.

> -----Original Message-----
> From: Jerry Fochtman [SMTP:[log in to unmask]]
> Sent: Friday, April 28, 2000 8:54 AM
> To:   [log in to unmask]
> Subject:      Re: Image hashing.
>
> Previously I said:
>
> At 07:15 AM 4/28/2000 -0500, Jerry Fochtman wrote:
>  >IMAGE uses the 'right most' 32 bits if the size of the binary key field
> is
>  >4 bytes or greater.  If the key field is 2 bytes, these bytes are placed
> in
>  >the right 2 bytes of the calculation field and the left 2 bytes set to
> zero.
>  >The reason whole numbers in real type key items greater than 4 bytes in
> size
>  >(eg. E4, R4 or larger) generates lots of secondaries is because the
> mantisa
>  >portion of the field (right most bytes) tends to be a consistent (zero)
> and
>  >when used in the modulo calculation, derives the same address value.
>
> Sorry, but I had overlooked that its not simply real values > 4 bytes, but
> essentially all real values that can cause this type of problem.  This is
> because the use of the exponential technique to represent the value in
> powers
> of 2 does not lend itself to the possibility of deriving an even
> distribution
> over the area represented by the capacity. (Gosh its been a long time
> since
> I've dealt with number theory, statistical theory, etc...!)
>
>
>
> /jf
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