Convert strings to their fullwidth versions

fullwidther.rb

# it turns out that "Ａ".ord - "A".ord is constant when you replace the two characters
# with, say "Ｂ" and "B", so ("B".ord + DIFFERENCE).to_s(16) == "ff22" and "\uff22"
# is "Ｂ". (Thanks, Unicode consortium.)
# 
# an exception is U+0020 space, which has IDEOGRAPHIC SPACE U+3000, but the two don't
# differ by DIFFERENCE == 65248 == 0xfee0, so you have to replace 20+65248 == 0xff00
# with 0x3000.

DIFFERENCE = 65248

def fullwidth(str)
  str.unpack("U*").map { |e| e + DIFFERENCE }.pack("U*").gsub("\uFF00", "\u3000")
end

fullwidth "B" #=> "Ｂ"

fullwidth "Goodbye, World... (parenthetical remark~~~ ...)"
#=> "Ｇｏｏｄｂｙｅ，　Ｗｏｒｌｄ．．．　（ｐａｒｅｎｔｈｅｔｉｃａｌ　ｒｅｍａｒｋ～～～　．．．）"