add back caching ws values, that was a memory bug of minetest and these numbers hardly use memory space I guess

src/mapgen_v6.lua

@@ -1,5 +1,6 @@
 -- https://github.com/paramat/meru/blob/master/init.lua#L52
 -- Parameters must match mgv6 biome noise
+
 local np_default = {
 	offset = 0,
 	scale = 1,
@@ -9,6 +10,7 @@ local np_default = {
 	persist = 0.5
 }
 
+
 -- 2D noise for coldness
 
 local mg = snow.mapgen
@@ -22,6 +24,7 @@ local np_cold = {
 	persist = 0.5
 }
 
+
 -- 2D noise for icetype
 
 local np_ice = {
@@ -33,6 +36,7 @@ local np_ice = {
 	persist = 0.5
 }
 
+
 -- Debugging function
 
 local biome_strings = {
@@ -55,6 +59,24 @@ local function do_ws_func(a, x)
 end
 
 
+-- caching functions
+
+local ws_lists = {}
+local function get_ws_list(a,x)
+	ws_lists[a] = ws_lists[a] or {}
+	local v = ws_lists[a][x]
+	if v then
+		return v
+	end
+	v = {}
+	for x=x,x + (80 - 1) do
+		local y = do_ws_func(a, x)
+		v[x] = y
+	end
+	ws_lists[a][x] = v
+	return v
+end
+
 local plantlike_ids = {}
 local function is_plantlike(id)
 	if plantlike_ids[id] ~= nil then
@@ -97,6 +119,7 @@ local function is_snowable(id)
 	return true
 end
 
+
 local c, replacements
 local function define_contents()
 	c = {
@@ -431,7 +454,11 @@ minetest.register_on_generated(function(minp, maxp, seed)
 			if test > 0 then
 				local maxh = math.floor(test*10)%10+1
 				if maxh ~= 1 then
-					local h = math.floor( do_ws_func(2, x) + do_ws_func(5, z)*5)%10+1
+					if not wsz then
+						wsz = get_ws_list(5, z0)
+						wsx = get_ws_list(2, x0)
+					end
+					local h = math.floor(wsx[x]+wsz[z]*5)%10+1
 					if h ~= 1 then
 						-- search for nearby snow
 						y = y+1
@@ -488,4 +515,3 @@ minetest.register_on_generated(function(minp, maxp, seed)
 		print("[snow] "..biome_string.." x "..minp.x.." z "..minp.z.." time "..chugent.." ms")
 	end
 end)
-