OpenEuphoria

RE: not_bits() not_working()

• Posted by rforno at tutopia.com Jun 27, 2003
• 433 views

The bit functions are in Eu (and Assembly, C, etc.) to use individual bits,
not their "global" meaning. So, you can compress 31 yes - no data in a
single integer, for example.

Assume you have a big file, each record containing an identifier from 1 to
1,000,000,000.
You want to scan the file and find which identifiers are missing and which
are duplicated.
Using a sequence occupying ~ 256Mb, you can get the job done by reading the
file only once, if you flag each identifier by means of the corresponding
bit in the sequence.
Regards.
----- Original Message -----
From: Al Getz <Xaxo at aol.com>
To: EUforum <EUforum at topica.com>
Sent: Thursday, June 26, 2003 4:07 PM
Subject: RE: not_bits() not_working()


>
>
> Matt Lewis wrote:
> >
> >
> > Al Getz wrote:
> >
> > > I've found that Euphorias not_bits() function doesnt really work
> > > correctly.
> > >
> > > For example:
> > >
> > > atom a,x
> > > a=2
> > >
> > > x=not_bits(a)
> > >
> > > --now x equals -3, which isnt correct.
> > > --x should be equal to the 8 digit hex equivalent of -3,
> > > --right?
> >
> > Actually, it is. not_bits() works exactly as it says it does (although
> > it does seem odd):
> >
> > "Results are treated as signed numbers. They will be negative when the
> > highest-order bit is 1." -- Refman
> >
> > So the bits are correct.  The quickest way to convert to unsigned (if
> > that's what you want) seems to be to have 4-bytes allocated and do a
> > poke4/peek4u after not_bits.  (I just tested this vs adding 2^32 and vs
> > using xor_bits against a constant equal to 2^32-1). (These were tested
> > with Win2K, P3, 1.1GHz)
> >
> > If you printf with %x (hex formatting) or use int_to_bits, you'll see
> > that the bits are correct.
> >
> > Matt Lewis
> >
>
> Hello Matt,
>
> I have been using poke4 and peek4u to convert because it seems
> to be the most reliable way to do it with only three ops, however
> now ill have to check out Carls idea too.  There is a chance that
> my argument will always be positive.
>
> I just cant help wondering why not_bits() doesnt work the way
> the other _bits functions work, or did i miss something?
> Is there any real use for getting a return value of -3 for
> not_bits(2) out there? anyone?
>
> Take care,
> Al
>
>
>
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