Function for using arbitrary digit systems to convert numbers to strings

arbase.lua

local function base (digit_list)
  local b = #digit_list
  if b == 0 then
    return function(number) return "" end
  elseif b == 1 then
    local mark = digit_list[1]
    return function(number)
      return string.rep(mark, number)
    end
  else
    return function(number)
      number=math.floor(number)
      
      if number == 0 then
        return digit_list[1]
      end
      
      local places={}
      local pow=0
      local digits=math.floor(math.log(number) / math.log(b))+1

      for pow=digits,1,-1 do
        places[#places+1] = digit_list[
          (number % b^pow
          -number % b^(pow-1))
            /b^(pow-1) + 1]
      end

      return table.concat(places)
    end
  end
end

local bbar = base{"|"}

local b2 = base{'0','1'}

local b10 = base{
  '0','1','2','3','4','5','6','7','8','9',
}

local bten = base{
  'zero','one','two','three','four','five','six','seven','eight','nine',
}

local b32 = base{
  '0','1','2','3','4','5','6','7','8','9',
  'A','B','C','D','E','F','G','H','J','K',
  'L','M','N','P','Q','R','S','T','U','V',
  'W','X'
}

the talk is on http://lua-list.2524044.n2.nabble.com/tostring-e-base-td6621781.html

another impl.

local math = require( 'math' ) 
local table = require( 'table' ) 
local assert = assert 
local tonumber = tonumber 
local abs, floor = math.abs, math.floor 

local base = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z' } 

local function tobase( aNumber, aBase ) 
    assert( aNumber, 'bad argument #1 to \'tobase\' (nil number)' ) 
    assert( aBase and aBase >= 2 and aBase <= #base, 'bad argument #2 to \'tobase\' (base out of range)' ) 

    local isNegative = aNumber < 0 
    local aNumber = abs( floor( tonumber( aNumber ) ) ) 
    local aBuffer = {} 

    repeat 
        aBuffer[ #aBuffer + 1 ] = base[ ( aNumber % aBase ) + 1 ] 
        aNumber = floor( aNumber / aBase ) 
    until aNumber == 0 

    if isNegative then 
        aBuffer[ #aBuffer + 1 ] = '-' 
    end 

    return table.concat( aBuffer ):reverse() 
end 

python based int2base

http://stackoverflow.com/questions/2267362/convert-integer-to-a-string-in-a-given-numeric-base-in-python

import string
digs = string.digits + string.lowercase

def int2base(x, base):
  if x < 0: sign = -1
  elif x==0: return '0'
  else: sign = 1
  x *= sign
  digits = []
  while x:
    digits.append(digs[x % base])
    x /= base
  if sign < 0:
    digits.append('-')
  digits.reverse()
  return ''.join(digits)