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From: Stephane Faroult <>
Date: Tue, 06 Jan 2004 02:13:46 -0800
Message-ID: <>


   This is what spontaneously comes to my mind and may not make a lot of sense in your case, but why do you need TWO bitmaps in the first place? Your second (Permission) bitmap uses 2 bits to store three states (no permission/P1/P2). This is enough to hold the STORAGE information as well,   eg

      00  Not stored
      01  Stored with no permission
      10  Stored with P1
      11  Stored with P2

 I of course assume, and may be wrong on this account, that storage is a pre-requisite for permission. Otherwise I would use 24 bits. I presume that your bitmaps don't appear as such, and therefore whether you have one or two fields is pretty irrelevant to the end-user. It looks to me easier to understand and maintain that some Rubik-cube-like bit-twiddling.


>----- ------- Original Message ------- -----
>From: "Bobak, Mark" <>
>To: Multiple recipients of list ORACLE-L
>Sent: Tue, 06 Jan 2004 01:39:25
>Well, since I can't sleep, I may as well try
>solving a problem.
>This is a bit odd, and I'm trying to think of the
>most efficient way to do
>it. I've set up some bitmaps in my app. Consider
>we have documents that
>we want to sell. In order to be able to sell a
>given doc, we need to have it
>stored in the vault and we also need to have
>negotiated the proper contract
>w/ the publisher. So, I've got two bitmaps,
>But, here's the hook. There are 8 different types
>of storage, so I have
>an 8 bit mask. However, for every storage type,
>there are two types of
>permission. So, I have a 16 bit permissions mask.
>What I'd like to do is take my 8-bit STORAGE mask,
>say it's 10110011
>and convert it to 1100111100001111. Note that all
>I did there was take
>each bit in the input mask, and make the same value
>repeat. So, 0 would
>become 00, 1 would become 11, 10 would become 1100.
> Does that make sense?
>Once I've done that, I can take my STORAGE mask
>that's now stretched to 16
>bits, and directly AND it with my PERMISSIONS mask.
>So, my question is: Is there a nice, scalable way
>to take my 8 bits and
>expand them into 16 bits, in the way that I'm
>describing? A clever bit
>twiddling expression would be perfect, but anything
>that's efficient and
>scalable will do. (The end product will be hidden
>behind a view or stored
>Any thoughts, anyone?
>Thanks in advance,

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Author: Stephane Faroult

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Received on Tue Jan 06 2004 - 04:13:46 CST

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