Hi,
Is it possible to store and manipulate binary data in Ruby?
As in the actual sequence of 1’s and 0’s. I’m curious in the
data-compression problem, but to be able to do any compression on a Ruby
string I need to be able to manipulate data at the bit level.
Does anyone know how this can be done?
–
Daniel Carrera
Graduate Teaching Assistant. Math Dept.
University of Maryland. (301) 405-5137
I can think of the following:
Bit operations w/ Fixnum, then Array#pack.
On Tue, May 06, 2003 at 05:17:01AM +0900, Daniel Carrera wrote:
Hi,
Is it possible to store and manipulate binary data in Ruby?
As in the actual sequence of 1’s and 0’s. I’m curious in the
data-compression problem, but to be able to do any compression on a Ruby
string I need to be able to manipulate data at the bit level.Does anyone know how this can be done?
–
_ _
__ __ | | ___ _ __ ___ __ _ _ __
'_ \ /| __/ __| '__ \ / ` | ’ \
) | (| | |__ \ | | | | | (| | | | |
.__/ _,|_|/| || ||_,|| |_|
Running Debian GNU/Linux Sid (unstable)
batsman dot geo at yahoo dot com
Hi,
Is it possible to store and manipulate binary data in Ruby?
As in the actual sequence of 1’s and 0’s. I’m curious in the
data-compression problem, but to be able to do any compression on a Ruby
string I need to be able to manipulate data at the bit level.Does anyone know how this can be done?
As I understand it, strings in Ruby store binary data, and can
be viewed as an array of 8-bit bytes.
dat = [0x12345678].pack(“N”)
=> “\0224Vx”
printf(“%x %x %x %x”, dat[0], dat[1], dat[2], dat[3])
12 34 56 78=> nil
dat[1] ^= 0xFF # twiddle some bits in the 2nd byte
=> 203
printf(“%x %x %x %x”, dat[0], dat[1], dat[2], dat[3])
12 cb 56 78=> nil
dat.unpack(“N”)
=> [315315832]
printf(“%x”, dat.unpack(“N”)[0])
12cb5678=> nil
So I don’t think you necessarily have to use pack & unpack,
unless you want to extract the binary data to some other format
easily (or you need to work with non byte-width data I guess.)
But if you start out with an empty string and write binary bytes
to it, for instance, you should just be able to write the string
to a file.
If you read a binary file into a string, you should be able to
tweak the bits on a byte-by-byte basis, and save the modified
binary data in the string back out to a file…
So I guess as long as byte-width access to binary data meets
your needs, Ruby strings are pretty ideal. 
Hope this helps,
Bill
From: “Daniel Carrera” dcarrera@math.umd.edu
----CUT----
#!/usr/bin/env ruby
require ‘bitset’
class BitSet; def = i, b; self.set i, b; end; end
b = BitSet.new 8
b[1], b[3], b[5] = 1, 1, 1
p b # >> 01010100
p eval(“#{b}b0”.reverse) # >> 42
----CUT----
-a
On Tue, 6 May 2003, Daniel Carrera wrote:
Hi,
Is it possible to store and manipulate binary data in Ruby?
As in the actual sequence of 1’s and 0’s. I’m curious in the
data-compression problem, but to be able to do any compression on a Ruby
string I need to be able to manipulate data at the bit level.Does anyone know how this can be done?
Ara Howard
NOAA Forecast Systems Laboratory
Information and Technology Services
Data Systems Group
R/FST 325 Broadway
Boulder, CO 80305-3328
Email: ara.t.howard@fsl.noaa.gov
Phone: 303-497-7238
Fax: 303-497-7259
====================================
Hi Daniel
Daniel Carrera wrote:
Is it possible to store and manipulate binary data in Ruby?
As in the actual sequence of 1’s and 0’s. I’m curious in the
data-compression problem, but to be able to do any compression on a Ruby
string I need to be able to manipulate data at the bit level.
You should have a look at the following methods:
Array#pack
String#unpack
Hope this helps,
–
Laurent
Is it possible to store and manipulate binary data in Ruby?
[snip]
I can think of the following:
Bit operations w/ Fixnum, then Array#pack.
Could you explain to me how to use Array#pack? PickAxe doesn’t contain
almost anything:
Pickaxe:
a = [ “a”, “b”, “c” ]
n = [ 65, 66, 67 ]
a.pack(“A3A3A3”)" # → “a b c”
a.pack(“a3a3a3”) # → “a\000\000b\000\000c\000\000”
n.pack(“ccc”) # → “ABC”
Where can I learn how to use Array#pack?
Thanks,
–
Daniel Carrera
Graduate Teaching Assistant. Math Dept.
University of Maryland. (301) 405-5137
Bill Kelly wrote:
Hi,
From: “Daniel Carrera” dcarrera@math.umd.edu
Just a quick example:
x = “hello”.unpack(“b*”).to_s →
“0001011010100110001101100011011011110110”
x[0] → 49 (i.e. 00010110)
Also, see sig. Hope that helps.
Regards,
Dan
–
p
[“010100101010111011001110001011100000010010000010011101101111011000101110000101101010011001001110000001000100101010101110010001101001111000000100000100101000011011000110110101101010011001001110”].pack(“b*”)
It’s in the Pickaxe, you just have to look a bit…
http://www.rubycentral.com/book/ref_c_array.html
search for “Template characters for Array#pack” which is a table of the
different packing codes. In the HTML it sits just after the definition of
‘include?’, which is inconveniently not next to ‘pack’…
The counterpart is String#unpack:
http://www.rubycentral.com/book/ref_c_string.html#String.unpack
(and its table of template characters is more sensibly placed
But if you just want to pick individual bits out of a binary String you
don’t need either:
a = “hello”
a[0] # 104 (= 0x68 = ASCII code for ‘h’)
a[1] # 101 (= 0x65 = ASCII code for ‘e’)
a[1][0] # 1 (bit 0 of 0x65)
a[1][1] # 0 (bit 1 of 0x65)
a[1][2] # 1 (bit 2 of 0x65)
i.e. String# extracts one byte as a Fixnum, and Fixnum# extracts one
bit as 0 or 1
Regards,
Brian.
On Tue, May 06, 2003 at 06:10:40AM +0900, Daniel Carrera wrote:
Could you explain to me how to use Array#pack? PickAxe doesn’t contain
almost anything:Pickaxe:
a = [ “a”, “b”, “c” ]
n = [ 65, 66, 67 ]
a.pack(“A3A3A3”)" # → “a b c”
a.pack(“a3a3a3”) # → “a\000\000b\000\000c\000\000”
n.pack(“ccc”) # → “ABC”Where can I learn how to use Array#pack?