string buffers using string.gsub faster than table.concat

[David Manura <dm.lua@...>]

Are there faster ways to concatenate a large number of strings in Lua
than the usually recommended table.concat approach described in PiL
2nd 11.6 "String Buffers"?  The following tests show that a trick with
string.gsub can be a little faster:

-- test.lua
local mode = arg[1] or 'A'
local N = arg[2] or 1000000
local M = arg[3] or 1
local result
if mode == 'A' then
  for i=1,M do
    result =  ((' '):rep(N):gsub('() ', function(i)
      return string.char(i % 256)
    end))
  end
elseif mode == 'B' then
  for i=1,M do
    local ts = {}
    for i=1,N do ts[#ts+1] = string.char(i % 256) end
    result = table.concat(ts)
  end
elseif mode == 'C' then
  for i=1,M do
    local ts = {}
    for i=1,N do
      ts[#ts+1] = string.char(i % 256)
      while #ts >= 2 and #ts[#ts] ==  #ts[#ts-1] do
        ts[#ts-1] = ts[#ts-1] .. ts[#ts]
        ts[#ts] = nil
      end
    end
    for i=#ts,2,-1 do
      ts[i-1] = ts[i-1] .. ts[i]
      ts[i] = nil
    end
    result = ts[1]
  end
elseif mode == 'D' then
  for i=1,M do
    local s = ""
    for i=1,N do s = s .. string.char(i % 256) end
    result = s
  end
end

# results for Lua 5.1, x86
$ for x in A B C D; do time test.lua $X; done
A: 0.72 0.79 0.78 s
B: 1.2 1.4 1.4 s
C: 3.0 2.6 2.6 s
D: (very long)

# for luajit 2.0-beta10
A: 0.49 0.49 0.47
B: 0.65 0.90 0.65
C: 1.7 1.9 1.8
D: (very long)