From: Rob Lee <robl@...>
Date: 2006-10-23T22:45:56+09:00
Subject: Re: Binary file modification


> It's already packed. The return value of the long expression will be a 3
> byte string which you can insert as you like (print it to the IO handle, 
> <<
> it to another string etc etc). The accumulator in the inject method is a
> string {|str,byte| ... might have been more readable, sorry.
> 
> ben

Sorry I should have studied it a little closer ...

I've tried the following and your re-packing doesn't seem to work :

f = open("testfile","wb")
num=359447
f.write(num.to_s(16)[0..2].instance_eval {(self.reverse + '0' * (6 - 
self.length)).reverse}.scan(/../).inject('') {|s,byte| s << 
byte.to_i(16)})
f.close
f = open("testfile","rb")
f.pos=0
puts f.read(3).unpack('H*').first.to_i(16)
f.close

=> 1404

It does seem to work for small values like 1024 but not larger ones.  I 
know there will be an upper limit to the integer size I can fit into the 
three bytes but the 359447 value is one I've taken from an existing file 
so I believe this is a valid integer to try and pack into these three 
bytes.

Any advice ?

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