Spell number

IntegerNumberInWords.lua

local append, concat, floor, abs = table.insert, table.concat, math.floor, math.abs
local num = {'one', 'two', 'three', 'four', 'five', 'six', 'seven', 'eight', 'nine', 'ten', 'eleven',
   'twelve', 'thirteen', 'fourteen', 'fifteen', 'sixteen', 'seventeen', 'eighteen', 'nineteen'}
local tens = {'twenty', 'thirty', 'forty', 'fifty', 'sixty', 'seventy', 'eighty', 'ninety'}
local bases = {{floor(1e18), ' quintillion'}, {floor(1e15), ' quadrillion'}, {floor(1e12), ' trillion'},
   {floor(1e9), ' billion'}, {1000000, ' million'}, {1000, ' thousand'}, {100, ' hundred'}}

local insert_word_AND = false  -- 101 = "one hundred and one" / "one hundred one"

local function IntegerNumberInWords(n)
   -- Returns a string (spelling of integer number n)
   -- n should be from -2^53 to 2^53  (-2^63 < n < 2^63 for integer argument in Lua 5.3)
   local str = {}
   if n < 0 then
      append(str, "minus")
   end
   n = floor(abs(n))
   if n == 0 then
      return "zero"
   end
   if n >= 1e21 then
      append(str, "infinity")
   else
      local AND
      for _, base in ipairs(bases) do
         local value = base[1]
         if n >= value then
            append(str, IntegerNumberInWords(n / value)..base[2])
            n, AND = n % value, insert_word_AND or nil
         end
      end
      if n > 0 then
         append(str, AND and "and")   -- a nice pun !
         append(str, num[n] or tens[floor(n/10)-1]..(n%10 ~= 0 and '-'..num[n%10] or ''))
      end
   end
   return concat(str, ' ')
end

-- Usage:
-- print(IntegerNumberInWords(-12345))