How to locate the bit in bits string?

[tuxagb]

On 28 Apr, 17:24, Li Wang <li.wan... at gmail.com> wrote:
> 2009/4/29 Tim Chase <python.l... at tim.thechases.com>:
>
> > Li Wang wrote:
>
> >> Hi:
>
> >> If I use an integer to represent bits:
> >> e.g. 99 represents '1100011'
>
> >> How can I locate, say the second bit of 99(i.e. '1')?
>
> >> Although bin(99)[4] could be used to locate it, this transform cost
> >> too much memory (99 only needs 2Bytes, while string '1100011' needs
> >> 7Bytes).
>
> >> Anyone knows how to locate  the second bit without using bin() function?
>
> > You mean
>
> >  def get_bit(number, bit):
> >    return (number >> bit) & 1
>
> > ?
>
> Hummm, I have tried this method too, the problem is its time
> complexity. If the length of my bits is n, then the time complexity is
> O(n). When I tried to implement this in practice, it did consume a lot
> of time.
>
> So do you know how could I locate the bit in O(1) time? Transform it
> into a string is a method, but takes too much space (when I try to
> process a 2M file, it used more than 100M memory.....).
>
> Thank you very much.
>
> > -tkc
>
> --
> Li
> ------
> Time is all we have
> and you may find one day
> you have less than you think

The my solution is good, but the Tim's solution is better, and it is O
(1) in time and space.
What is you search? I dont'know you general problem, but search the
value of a bit in a 2M file ...
is strange .....

Hi.