1 files changed, 40 insertions, 0 deletions
diff --git a/src/common/random.lua b/src/common/random.lua
new file mode 100644
index 0000000..4fbbed3
--- /dev/null
+++ b/src/common/random.lua
@@ -0,0 +1,40 @@
+skycraft.random = {
+    choices = {},
+    probabilities = {},
+    csum = {},
+    sum = 0
+}
+
+skycraft.random.__index = skycraft.random
+
+function skycraft.random:new(o)
+    o = o or {}
+    setmetatable(o, self)
+    o.choices = {}
+    o.probabilities = {}
+    o.csum = {}
+    o.sum = 0
+    return o
+end
+
+function skycraft.random:calc_csum()
+	self.sum = 0
+    for i, choice in ipairs(self.choices) do
+        self.sum = self.sum + self.probabilities[choice]
+        self.csum[choice] = self.sum
+    end
+end
+
+function skycraft.random:choose()
+    local r = math.random() + math.random(0, self.sum - 1)
+    for i, choice in pairs(self.choices) do
+        if r < self.csum[choice] then
+            return choice
+        end
+    end
+end
+
+function skycraft.random:add_choice(choice, probability)
+    table.insert(self.choices, choice)
+    self.probabilities[choice] = probability
+end