From 44a98a7d415e44d55bd737c8a2a7460ec692fe4c Mon Sep 17 00:00:00 2001
From: Lars Mueller <appgurulars@gmx.de>
Date: Sun, 11 Jul 2021 16:52:41 +0200
Subject: [PATCH] Add hashlist

---
 hashlist.lua | 90 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 test.lua     | 13 ++++++++
 2 files changed, 103 insertions(+)
 create mode 100644 hashlist.lua

diff --git a/hashlist.lua b/hashlist.lua
new file mode 100644
index 0000000..5e84623
--- /dev/null
+++ b/hashlist.lua
@@ -0,0 +1,90 @@
+-- Localize globals
+local setmetatable = setmetatable
+
+-- Table based list, can handle at most 2^52 pushes
+local list = {}
+-- TODO use __len for Lua version > 5.1
+local metatable = {__index = list}
+list.metatable = metatable
+
+-- Takes a list
+function list:new()
+    self.head = 0
+    self.length = #self
+    return setmetatable(self, metatable)
+end
+
+function list:in_bounds(index)
+    return index >= 1 and index <= self.length
+end
+
+function list:get(index)
+    return self[self.head + index]
+end
+
+function list:set(index, value)
+    assert(value ~= nil)
+    self[self.head + index] = value
+end
+
+function list:len()
+    return self.length
+end
+
+function list:ipairs()
+    local index = 1
+    return function()
+        if index > self.length then
+            return
+        end
+        return index, self[self.head + index]
+    end
+end
+
+function list:rpairs()
+    local index = self.length
+    return function()
+        if index < 1 then
+            return
+        end
+        return index, self[self.head + index]
+    end
+end
+
+function list:push_tail(value)
+    assert(value ~= nil)
+    self.length = self.length + 1
+    self[self.head + self.length] = value
+end
+
+function list:get_tail()
+    return self[self.head + self.length]
+end
+
+function list:pop_tail()
+    if self.length == 0 then return end
+    local value = self:get_tail()
+    self[self.head + self.length] = nil
+    self.length = self.length - 1
+    return value
+end
+
+function list:push_head(value)
+    self[self.head] = value
+    self.head = self.head - 1
+    self.length = self.length + 1
+end
+
+function list:get_head()
+    return self[self.head + 1]
+end
+
+function list:pop_head()
+    if self.length == 0 then return end
+    local value = self:get_head()
+    self.head = self.head + 1
+    self[self.head] = nil
+    return value
+end
+
+return list
\ No newline at end of file
diff --git a/test.lua b/test.lua
index 2ddabf2..34d776f 100644
--- a/test.lua
+++ b/test.lua
@@ -99,6 +99,19 @@ do
 	end
 end
 
+-- hashlist
+do
+	local n = 100
+	local list = hashlist.new{}
+	for i = 1, n do
+		list:push_tail(i)
+	end
+	for i = 1, n do
+		local head = list:get_head()
+		assert(head == list:pop_head(i) and head == i)
+	end
+end
+
 -- ranked set
 do
 	local n = 100