Use voxelmanip data buffer memory optimisation

Reuse a single table for content ids to reduce memory use.
Add DEBUG parameter to control printing of mapchunk generation time,
set to false as default.
Add missing noise parameters (parameters are default and unchanged).

init.lua

@@ -3,6 +3,7 @@
 local NETHER_DEPTH = -5000
 local TCAVE = 0.6
 local BLEND = 128
+local DEBUG = false
 
 
 -- 3D noise
@@ -13,7 +14,9 @@ local np_cave = {
 	spread = {x = 384, y = 128, z = 384}, -- squashed 3:1
 	seed = 59033,
 	octaves = 5,
-	persist = 0.7
+	persist = 0.7,
+	lacunarity = 2.0,
+	--flags = ""
 }
 
 
@@ -534,10 +537,11 @@ minetest.register_craft({
 
 -- Mapgen
 
--- Initialize noise object and localise noise buffer
+-- Initialize noise object, localise noise and data buffers
 
 local nobj_cave = nil
 local nbuf_cave
+local dbuf
 
 
 -- Content ids
@@ -589,7 +593,7 @@ minetest.register_on_generated(function(minp, maxp, seed)
 
 	local vm, emin, emax = minetest.get_mapgen_object("voxelmanip")
 	local area = VoxelArea:new{MinEdge = emin, MaxEdge = emax}
-	local data = vm:get_data()
+	local data = vm:get_data(dbuf)
 
 	local x11 = emax.x -- Limits of mapchunk plus mapblock shell
 	local y11 = emax.y
@@ -678,6 +682,8 @@ minetest.register_on_generated(function(minp, maxp, seed)
 	vm:update_liquids()
 	vm:write_to_map()
 
-	local chugent = math.ceil((os.clock() - t1) * 1000)
-	print ("[nether] generate chunk " .. chugent .. " ms")
+	if DEBUG then
+		local chugent = math.ceil((os.clock() - t1) * 1000)
+		print ("[nether] generate chunk " .. chugent .. " ms")
+	end
 end)