Re: manipulating bits not bytes-Enthusiasts level question

[HyperHacker <hyperhacker@...>]

On Sat, Sep 4, 2010 at 07:15, Patrick Mc(avery
<spell_gooder_now@spellingbeewinnars.org> wrote:
> I am having no trouble at all using Lua to manipulate bytes according to PIL
> but on P198 it says
>
> 'you can even do pattern matching over binary data'
>
> I would like to be able read and manipulate bits not bytes.
>
> The code below manipulates a few "1"'s but should change thousands.
>
>
> bin = io.open('29fb.bin', 'r') --29fb is 512 KB I am on Linux no "rb"
> bin_all = bin:read("*all")
> bin_zero, ntimes  = bin_all.gsub(bin_all, '1', '0')
>
> print(ntimes) --> 20 --should be way more times then this
>
> Is there also a way to convert binary to hex in pure Lua, I know Mike Pall
> has a great library but it is there a way to do this in pure Lua?
>
> Is there also a way to read one bit? read(1) is one byte, is there a way to
> read one bit?
>
> Thanks for reading-Patrick
>
>
>

There's no built-in function to read a single bit; you should be able
to write one fairly trivially that reads a byte and returns only a
specified bit of it, or converts a string to a series of zeros and
ones and back.

BTW, "*all" is unnecessary in read; you only need "*a". The manual
doesn't specify what unrecognized formats will do, so this is
undefined behaviour and might not work in other implementations.

-- 
Sent from my toaster.