What is causing this undefined method error on a string in Ruby on Rails?

Question

In this Ruby on Rails helper, there is the following method:

# Convert an 8-bit or 16-bit string to an array of big-endian words
# In 8-bit function, characters >255 have their hi-byte silently ignored.
def str2binb(str)
    bin = []
    mask = (1 << $chrsz) - 1
    #for(var i = 0; i < str.length * $chrsz; i += $chrsz)
    i = 0
    while(i < str.length * $chrsz)
        bin[i>>5] ||= 0
        p 'i'
        p i
        p '$chrsz'
        p $chrsz
        p 'str[i / $chrsz]'
        p str[i / $chrsz]
        p 'mask'
        p mask
        bin[i>>5] |= (str[i / $chrsz] & mask) << (32 - $chrsz - i%32)
        i += $chrsz
    end
    return bin
end

When run, this error occurs on the bin[i>>5] |= (str[i / $chrsz] & mask) << (32 - $chrsz - i%32) line:

ActionView::Template::Error (undefined method `&' for "J":String)

I don't understand how & is being used in this instance. How can I resolve this error? I am using Rails 3.2.0 and Ruby 1.9.2.

Here is the logging output:

"i"
0
"$chrsz"
8
"str[i / $chrsz]"
"J"
"mask"
255

Anthony Alberto · Accepted Answer · 2012-08-06 11:21:34Z

4

My guess is that this script is working on Ruby 1.8 but fails in Ruby 1.9 because Ruby1.9 outputs b when accessing "bla"[0] instead of the ASCII value of the char as it used to be in Ruby1.8.

You should be able to replace the problematic line by this :

bin[i>>5] |= (str.getbyte(i / $chrsz) & mask) << (32 - $chrsz - i%32)

Or using ord instead :

bin[i>>5] |= (str[(i / $chrsz)].ord & mask) << (32 - $chrsz - i%32)

edited Aug 6, 2012 at 11:21

answered Aug 6, 2012 at 4:16

Anthony Alberto

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