NEWBIE QUESTION - recode in Ruby

Rails
1

I wish to recode the following php code to ruby:

function text_decrypt_symbol($s, $i) {

$s is a text-encoded string, $i is index of 2-char code. function

returns number in range 0-255

     return (ord(substr($s, $i, 1)) - 100)*16 + ord(substr($s, $i

+1, 1)) - 100;
}

function text_decrypt($s) {

 if ($s == "")
     return $s;
 $enc = 85 ^ text_decrypt_symbol($s, 0);
 for ($i = 2; $i < strlen($s); $i+=2) { # $i=2 to skip salt
     $result .= chr(text_decrypt_symbol($s, $i) ^ $enc++);
     if ($enc > 255)
         $enc = 0;
 }
 return $result;

}

As I have stated I am a ruby newbie but thus far I have produced this:

def text_decrypt(value)
enc = 85 ^ text_decrypt_symbol(value, 0);

 i = 2

 while i < value.length
     curchar = text_decrypt_symbol(value, i) ^ enc++
     result += curchar.chr
     if enc > 255
         enc = 0
     end

     i+=2
 end
 return result;

end
def text_decrypt_symbol(value, value2)
char1 = value[value2, 1]
char2 = value[value2+1, 1]

 return (char1.chr - 100)*16 + char2.chr - 100;

end

Apparently the .chr method requires an integer to work. Anyone have
any advice?