From: "Dalthon [BR]" <efqdalton@...>
Date: 2009-11-19T20:25:30+09:00
Subject: Re: open a binary file-read bit-change bit-update same file

You can synchronize io setting file.sync = true to update on the same
file object

On 19 nov, 07:20, Robert Klemme <shortcut...@googlemail.com> wrote:
> 2009/11/19 Sniper Abandon <sathish.salem.1...@gmail.com>:
>
>
>
> > my Aim is i want to encrypt a file
>
> > i want to open a binary file
>
> > i want to read the 1-st bit
> > if the bit is "1" then update that position bit to "0" instantly
> > if the bit is "0" then update that position bit to "1" instantly
>
> > then i have to read 2-nd bit
> > do the same thing like above conversion
> > .......
> > .......
> > like i want to do this for all bit of that file
>
> > ---------------------
>
> > i know we can read the file into a array then we can do the
> > modification,etc
> > but i want to update on that same file object, and the file size may be
> > more then 1 GB
>
> > is it possible?
>
> Anything is possible.  But doing it bitwise is extremely inefficient.
> You should rather do it in chunks of, say, 1025 or 512 bytes or - even
> better - use the cluster size of your file system.
>
> XOR will be useful
>
> irb(main):004:0> a = 11
> => 11
> irb(main):005:0> sprintf "%08b -> %08b", a, a ^ 0xFF
> => "00001011 -> 11110100"
>
> Kind regards
>
> robert
>
> --
> remember.guy do |as, often| as.you_can - without endhttp://blog.rubybestpractices.com/