perf(shuffle): better bitwise xor for random integer (#44)

feat(policy): add `reverse_order` policy

Author: linrongbin16

README.md

@@ -32,11 +32,11 @@ It use offline github actions to weekly collect and update the most popular Vim/
 
 It install color plugins via git submodules instead of copy-paste source code, so you get continuously updates from original authors instead of me, e.g. it only transport and manage, not produce.
 
-It allow you play them with multiple playback settings:
+It allow you play them with multiple playback settings (policies):
 
 - Suffle playback.
 - Play in order.
-- Play in reverse order (todo).
+- Play in reverse order.
 - Single cycle (todo).
 - Specific color name (todo).
 
@@ -102,7 +102,7 @@ require('pckr').add({
 
 ```lua
 require('colorbox').setup({
-    --- @type "shuffle"|"inorder"|"single"
+    --- @type "shuffle"|"in_order"|"reverse_order"|"single"
     policy = "shuffle",
 
     --- @type "startup"|"interval"|"filetype"

lua/colorbox.lua

@@ -6,7 +6,7 @@ local json = require("colorbox.json")
 --- @alias colorbox.Options table<any, any>
 --- @type colorbox.Options
 local Defaults = {
-    --- @type "shuffle"|"inorder"|"single"
+    --- @type "shuffle"|"in_order"|"reverse_order"|"single"
     policy = "shuffle",
 
     --- @type "startup"|"interval"|"filetype"
@@ -160,7 +160,7 @@ local function _policy_shuffle()
     end
 end
 
-local function _policy_inorder()
+local function _policy_in_order()
     if #FilteredColorNamesList > 0 then
         local previous_track = _load_previous_track() --[[@as PreviousTrack]]
         local i = previous_track == nil and 0
@@ -174,14 +174,31 @@ local function _policy_inorder()
     end
 end
 
+local function _policy_reverse_order()
+    if #FilteredColorNamesList > 0 then
+        local previous_track = _load_previous_track() --[[@as PreviousTrack]]
+        local i = previous_track == nil and 0
+            or (
+                previous_track.color_number - 1 < 0
+                    and (#FilteredColorNamesList - 1)
+                or previous_track.color_number - 1
+            )
+        local color = FilteredColorNamesList[i + 1]
+        vim.cmd(string.format([[color %s]], color))
+        _save_previous_track(color, i)
+    end
+end
+
 local function _policy()
     if Configs.background == "dark" or Configs.background == "light" then
         vim.cmd(string.format([[set background=%s]], Configs.background))
     end
     if Configs.policy == "shuffle" then
         _policy_shuffle()
-    elseif Configs.policy == "inorder" then
-        _policy_inorder()
+    elseif Configs.policy == "in_order" then
+        _policy_in_order()
+    elseif Configs.policy == "reverse_order" then
+        _policy_reverse_order()
     end
 end
 

lua/colorbox/utils.lua

@@ -1,3 +1,21 @@
+-- Returns the XOR of two binary numbers
+--- @param a integer
+--- @param b integer
+--- @return integer
+local function bitwise_xor(a, b)
+    local r = 0
+    local f = math.floor
+    for i = 0, 31 do
+        local x = a / 2 + b / 2
+        if x ~= f(x) then
+            r = r + 2 ^ i
+        end
+        a = f(a / 2)
+        b = f(b / 2)
+    end
+    return r
+end
+
 --- @param l any[]
 --- @param f fun(v:any):number
 --- @return number
@@ -25,9 +43,9 @@ local function randint(maximal)
     local s2, s3 = vim.loop.gettimeofday()
     local s4 = math.random()
     local r = math_mod(s1, maximal)
-    r = math_mod(r * 3 + s2, maximal)
-    r = math_mod(r * 7 + s3, maximal)
-    r = math_mod(r * 11 + s4, maximal)
+    r = math_mod(bitwise_xor(r, s2 or 3), maximal)
+    r = math_mod(bitwise_xor(r, s3 or 7), maximal)
+    r = math_mod(bitwise_xor(r, s4 or 11), maximal)
     return r
 end