From: Dale Martenson <devlists-ruby-talk@...>
Date: 2006-08-02T06:33:43+09:00
Subject: Re: Binary numbers


On Wednesday, August 02, 2006, at 5:46 AM, Kim Pedersen wrote:
>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?

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 Martenson



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