Binary numbers

Ruby
1

Hi,

I have some data with binary numbers.
e.g. a 3 byte string could be 0x01216f which is 74095 decimal.
To do this conversion in ruby I’ve come up with:

def binum(bs)
n = e = 0
bs.reverse.each_byte do |c|
n += c * 256 ** e
e += 1
end
n
end

bs = ‘’
bs << 0x01 << 0x21 << 0x6f

puts binum(bs) => 74095

Now some data are signed binary numbers stored as two’s complement.
e.g. 0xfede91 which is -74095 decimal.

How can I do this conversion in ruby?

Best regards,
Kim

2

On Wednesday, August 02, 2006, at 5:46 AM, Kim P. wrote:

   e += 1

e.g. 0xfede91 which is -74095 decimal.

How can I do this conversion in ruby?

def binum(bs)
result = 0
bs.unpack(“cCC”).each {|b| result = (result << 8) | b }
result
end

bs = ‘’
bs << 0x01 << 0x21 << 0x6f

puts binum(bs)

bs = ‘’
bs << 0xfe << 0xde << 0x91

puts binum(bs)

The above code extracts the first byte as a signed 8-bit integer and the
rest of the bytes as unsigned 8-bit integers. Each iteration through the
loop shift the result to construct the proper value.

–Dale M.

3

On Aug 1, 2006, at 4:33 PM, Dale M. wrote:

def binum(bs)
result = 0
bs.unpack(“cCC”).each {|b| result = (result << 8) | b }
result
end

That’s just crying out for inject():

bs.unpack(“cCC”).inject(0) { |res, b| (res << 8) | b }

:wink:

James Edward G. II

4

James Edward G. II wrote:

bs.unpack(“cCC”).inject(0) { |res, b| (res << 8) | b }

:wink:

James Edward G. II
Thanks,
ps. just bought your ruby quiz book :slight_smile:

5

Dale M. wrote:

bs.reverse.each_byte do |c|

end

The above code extracts the first byte as a signed 8-bit integer and the
rest of the bytes as unsigned 8-bit integers. Each iteration through the
loop shift the result to construct the proper value.

–Dale M.

Great!
Thanks
Kim

BTW, the length of the string may vary from 1 to 8. I’ll have to adjust
for that.

6

On 8/2/06, Kim P. [email protected] wrote:

n = e = 0
puts binum(bs) => 74095
result
puts binum(bs)

BTW, the length of the string may vary from 1 to 8. I’ll have to adjust
for that.

For variable length;

c.unpack(“cC*”).inject(0) { |res, b| (res << 8) | b }