impl id freelist

evolved.lua

@@ -6,29 +6,133 @@ local evolved = {}
 ---@alias evolved.fragment evolved.id
 ---@alias evolved.component any
 
----@return evolved.id
----@nodiscard
-function evolved.id() end
+---
+---
+---
+---
+---
+
+local __freelist_ids = {} ---@type evolved.id[]
+local __available_idx = 0 ---@type integer
+
+---
+---
+---
+---
+---
 
 ---@param index integer
 ---@param version integer
 ---@return evolved.id
 ---@nodiscard
-function evolved.pack(index, version) end
+local function __pack_id(index, version)
+    assert(index >= 1 and index <= 0xFFFFF, 'id index out of range [1;0xFFFFF]')
+    assert(version >= 1 and version <= 0x7FF, 'id version out of range [1;0x7FF]')
+    return index + version * 0x100000
+end
 
 ---@param id evolved.id
 ---@return integer index
 ---@return integer version
 ---@nodiscard
-function evolved.unpack(id) end
+local function __unpack_id(id)
+    local index = id % 0x100000
+    local version = (id - index) / 0x100000
+    return index, version
+end
+
+---@return evolved.id
+---@nodiscard
+local function __acquire_id()
+    if __available_idx ~= 0 then
+        local index = __available_idx
+        local freelist_id = __freelist_ids[index]
+        __available_idx = freelist_id % 0x100000
+        local version = freelist_id - __available_idx
+
+        local acquired_id = index + version
+        __freelist_ids[index] = acquired_id
+        return acquired_id
+    else
+        if #__freelist_ids == 0xFFFFF then
+            error('id index overflow', 2)
+        end
+
+        local index = #__freelist_ids + 1
+        local version = 0x100000
+
+        local acquired_id = index + version
+        __freelist_ids[index] = acquired_id
+        return acquired_id
+    end
+end
 
 ---@param id evolved.id
 ---@return boolean
 ---@nodiscard
-function evolved.alive(id) end
+local function __alive_id(id)
+    local index = id % 0x100000
+    return __freelist_ids[index] == id
+end
 
 ---@param id evolved.id
-function evolved.destroy(id) end
+local function __release_id(id)
+    local index = id % 0x100000
+    local version = id - index
+
+    if __freelist_ids[index] ~= id then
+        error('id is not acquired or already released', 2)
+    end
+
+    version = version == 0x7FF00000
+        and 0x100000
+        or version + 0x100000
+
+    __freelist_ids[index] = __available_idx + version
+    __available_idx = index
+end
+
+---
+---
+---
+---
+---
+
+---@return evolved.id
+---@nodiscard
+function evolved.id()
+    return __acquire_id()
+end
+
+---@param index integer
+---@param version integer
+---@return evolved.id
+---@nodiscard
+function evolved.pack(index, version)
+    return __pack_id(index, version)
+end
+
+---@param id evolved.id
+---@return integer index
+---@return integer version
+---@nodiscard
+function evolved.unpack(id)
+    return __unpack_id(id)
+end
+
+---@param id evolved.id
+---@return boolean
+---@nodiscard
+function evolved.alive(id)
+    return __alive_id(id)
+end
+
+---@param id evolved.id
+function evolved.destroy(id)
+    if __alive_id(id) then
+        __release_id(id)
+    end
+end
 
 ---@param entity evolved.entity
 ---@param ... evolved.fragment fragments