qsort.lua

local function prequire(name) local success, result = pcall(require, name); return success and result end
local bench = script and require(script.Parent.bench_support) or prequire("bench_support") or require("../bench_support")

function test()

  -- two implementations of a sort function
  -- this is an example only. Lua has now a built-in function "sort"

  -- extracted from Programming Pearls, page 110
  function qsort(x,l,u,f)
  if l<u then
    local m=math.random(u-(l-1))+l-1	-- choose a random pivot in range l..u
    x[l],x[m]=x[m],x[l]			-- swap pivot to first position
    local t=x[l]				-- pivot value
    m=l
    local i=l+1
    while i<=u do
      -- invariant: x[l+1..m] < t <= x[m+1..i-1]
      if f(x[i],t) then
        m=m+1
        x[m],x[i]=x[i],x[m]		-- swap x[i] and x[m]
      end
      i=i+1
    end
    x[l],x[m]=x[m],x[l]			-- swap pivot to a valid place
    -- x[l+1..m-1] < x[m] <= x[m+1..u]
    qsort(x,l,m-1,f)
    qsort(x,m+1,u,f)
  end
  end

  function selectionsort(x,n,f)
  local i=1
  while i<=n do
    local m,j=i,i+1
    while j<=n do
    if f(x[j],x[m]) then m=j end
    j=j+1
    end
  x[i],x[m]=x[m],x[i]			-- swap x[i] and x[m]
  i=i+1
  end
  end

  --function show(m,x)
  -- io.write(m,"\n\t")
  -- local i=1
  -- while x[i] do
  --  io.write(x[i])
  --  i=i+1
  --  if x[i] then io.write(",") end
  -- end
  -- io.write("\n")
  --end

  function testsorts(x)
  local n=1
  while x[n] do n=n+1 end; n=n-1		-- count elements
  --show("original",x)
  qsort(x,1,n,function (x,y) return x<y end)
  --show("after quicksort",x)
  selectionsort(x,n,function (x,y) return x>y end)
  --show("after reverse selection sort",x)
  qsort(x,1,n,function (x,y) return x<y end)
  --show("after quicksort again",x)
  end

  -- array to be sorted
  x={"Jan","Feb","Mar","Apr","May","Jun","Jul","Aug","Sep","Oct","Nov","Dec"}

  local ts0 = os.clock()
  for loops=1,10000 do
    testsorts(x)
  end
  local ts1 = os.clock()

  return ts1 - ts0
end

bench.runCode(test, "qsort")