Better growth factor for arrays

haskell-effectful · Dec 22, 2024 · 2d54743 · 2d54743
1 parent 54236f4
commit 2d54743
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Showing 2 changed files with 13 additions and 6 deletions.
diff --git a/effectful-core/src/Effectful/Internal/Env.hs b/effectful-core/src/Effectful/Internal/Env.hs
@@ -477,7 +477,7 @@ insertEffect storage e f = do
         Storage (bumpVersion version) (StorageData (size + 1) vs0 es0 fs0)
       pure $ Ref size version
     EQ -> do
-      let len = doubleCapacity len0
+      let len = growCapacity len0
       vs <- newPrimArray len
       es <- newSmallArray len undefinedEffect
       fs <- newSmallArray len undefinedRelinker
@@ -511,10 +511,6 @@ deleteEffect storage (Ref ref version) = do
 relinkEnv :: IORef' Storage -> Env es -> IO (Env es)
 relinkEnv storage (Env offset refs _) = pure $ Env offset refs storage
 
--- | Double the capacity of an array.
-doubleCapacity :: Int -> Int
-doubleCapacity n = max 1 n * 2
-
 undefinedVersion :: Version
 undefinedVersion = Version 0
 

diff --git a/effectful-core/src/Effectful/Internal/Utils.hs b/effectful-core/src/Effectful/Internal/Utils.hs
@@ -18,8 +18,11 @@ module Effectful.Internal.Utils
   , Unique
   , newUnique
 
-  -- * CallStack
+    -- * CallStack
   , thawCallStack
+
+    -- * Array capacity
+  , growCapacity
   ) where
 
 import Control.Exception
@@ -129,3 +132,11 @@ thawCallStack :: CallStack -> CallStack
 thawCallStack = \case
   FreezeCallStack cs -> cs
   cs -> cs
+
+----------------------------------------
+
+-- | Grow capacity of an array.
+--
+-- See https://archive.ph/Z2R8w.
+growCapacity :: Int -> Int
+growCapacity n = 1 + quot (n * 3) 2