open a binary file-read bit-change bit-update same file

[Sniper Abandon]

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?
any idea and help is very much appreciated

 

[Robert Klemme]

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

 

[Dalthon [BR]]

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

 

[Robert Klemme]

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

That does only change the point in time _when_ the change in the file
can be observed by other processes but it does not affect _where_ the
changes are written. For that (i.e. writing to the same file) you
need File.open(name, "r+") anyway.

If you use that option and do "bitwise" updates (actually only
bytewise is possible) efficiency will drop even more dramatically.

Kind regards

robert