Re: D'oh, forgot my title! (Bit twiddling and bit manipulation...)

From: <jo_holvoet_at_amis.com>
Date: Tue, 06 Jan 2004 06:09:26 -0800
Message-ID: <F001.005DBD86.20040106060926@fatcity.com>

Maybe a lookup table filled once with 256 input/output pairs ?

mvg/regards

Connor McDonald <hamcdc_at_yahoo.co.uk>
Sent by: ml-errors_at_fatcity.com
01/06/2004 14:29
Please respond to ORACLE-L

        To:     Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
        cc: 
        Subject:        Re: D'oh, forgot my title!  (Bit twiddling and bit manipulation...)

As a first cut, bit 'i' appears to map to a new value of power(2,i*2-1)*1.5

8th bit set
= 10000000 binary
= 128 decimal

1100000000000000 under new scheme
49152 decimal
power(2,8*2-1)*1.5

so you could have something like:

new_num := 0;
x := 1;
for i in 0 .. 7 loop
if bitand(orig_num,x) = x then

      new_num := new_num + x*x*3;
  end if;
  x := x*2
end loop;

or something like that...

Cheers
Connor

"Bobak, Mark" <Mark.Bobak_at_il.proquest.com> wrote:
> Sorry, first time I sent this, I typoed the mailing
> list address, when I
> cut-and-paste to resend, I forgot the title.....
>
>
> -----Original Message-----
> From: Bobak, Mark
> Sent: Tue 1/6/2004 4:39 AM
> To: Multiple recipients of list ORACLE-L
> Cc:
> Subject:
> Hi,
>
> 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, STORAGE
> and PERMISSIONS.
>
> 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
> procedure.)
>
> Any thoughts, anyone?
>
> Thanks in advance,
>
> -Mark
> --
> Please see the official ORACLE-L FAQ:
> http://www.orafaq.net
> --
> Author: Bobak, Mark
> INET: Mark.Bobak_at_il.proquest.com
>
> Fat City Network Services -- 858-538-5051
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> ATTACHMENT part 2 application/ms-tnef

name=winmail.dat

Connor McDonald
web: http://www.oracledba.co.uk
web: http://www.oaktable.net
email: connor_mcdonald_at_yahoo.com

"GIVE a man a fish and he will eat for a day. But TEACH him how to fish, and...he will sit in a boat and drink beer all day"

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Author: 
  INET: jo_holvoet_at_amis.com

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Received on Tue Jan 06 2004 - 08:09:26 CST