improve UUID functionality

mods/CORE/mcl_util/init.lua

@@ -689,13 +689,19 @@ function mcl_util.trace_nodes(pos, dir, allowed_nodes, limit)
 
 	return nil, limit, nil
 end
-function mcl_util.gen_uuid()
-	-- Generate a random 128-bit ID that can be assumed to be unique
-	-- To have a 1% chance of a collision, there would have to be 1.6x10^76 IDs generated
-	-- https://en.wikipedia.org/wiki/Birthday_problem#Probability_table
+
+-- Make a local random to guard against someone misusing math.randomseed
+local uuid_rng = PcgRandom(bit.bxor(math.random(0xFFFFFFFF), os.time()))
+--- Generate a random 128-bit ID that can be assumed to be unique
+--- To have a 1% chance of a collision, there would have to be 1.6x10^76 IDs generated
+--- https://en.wikipedia.org/wiki/Birthday_problem#Probability_table
+--- @param len32 integer: length in 32-bit units, optional, default 4 (128 bit)
+--- @return string: UUID string, 8xlen32 characters, default 32
+function mcl_util.gen_uuid(len32)
+	len32 = (len32 and len32 > 0) and len32 or 4 -- len32 might be nil
 	local u = {}
-	for i = 1,16 do
-		u[#u + 1] = string.format("%02X",math.random(1,255))
+	for i = 1,len32 do
+		u[#u + 1] = bit.tohex(uuid_rng:next()) -- 32 bit at a time
 	end
 	return table.concat(u)
 end

mods/ENTITIES/mcl_entity_invs/init.lua

@@ -163,8 +163,7 @@ function mcl_entity_invs.register_inv(entity_name,show_name,size,no_on_righclick
 			self._items = d._items
 			self._inv_size = d._inv_size
 		else
-			self._inv_id="entity_inv_"..minetest.sha1(minetest.get_gametime()..minetest.pos_to_string(self.object:get_pos())..tostring(math.random()))
-			--gametime and position for collision safety and math.random salt to protect against position brute-force
+			self._inv_id="entity_inv_"..mcl_util.gen_uuid()
 		end
 		return r
 	end

mods/ENTITIES/mobs_mc/villager.lua

@@ -2284,7 +2284,7 @@ mcl_mobs.register_mob("mobs_mc:villager", {
 			set_textures(self)
 			return
 		end
-		self._id=minetest.sha1(minetest.get_gametime()..minetest.pos_to_string(self.object:get_pos())..tostring(math.random()))
+		self._id=mcl_util.gen_uuid()
 		set_textures(self)
 	end,
 	on_die = function(self, pos, cmi_cause)