Add function to compute an ideal batch size from a number of inputs

cardano-foundation · Oct 18, 2019 · 9f8a886 · 9f8a886
1 parent 63a18b4
commit 9f8a886
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Showing 3 changed files with 46 additions and 4 deletions.
diff --git a/lib/core/src/Cardano/Wallet/Primitive/CoinSelection/Migration.hs b/lib/core/src/Cardano/Wallet/Primitive/CoinSelection/Migration.hs
@@ -10,12 +10,17 @@
 
 module Cardano.Wallet.Primitive.CoinSelection.Migration
     ( selectCoinsForMigration
+    , idealBatchSize
     ) where
 
 import Prelude
 
 import Cardano.Wallet.Primitive.CoinSelection
-    ( CoinSelection (..), changeBalance, inputBalance )
+    ( CoinSelection (..)
+    , CoinSelectionOptions (..)
+    , changeBalance
+    , inputBalance
+    )
 import Cardano.Wallet.Primitive.Fee
     ( Fee (..), FeeOptions (..) )
 import Cardano.Wallet.Primitive.Types
@@ -122,3 +127,17 @@ selectCoinsForMigration feeOpts batchSize utxo =
         let (batch, rest) = splitAt (fromIntegral batchSize) xs
         put rest
         pure batch
+
+-- | Try to find a fix "ideal" number of input transactions that would generate
+-- rather balanced transactions.
+idealBatchSize :: CoinSelectionOptions e -> Int
+idealBatchSize coinselOpts = fromIntegral (fixPoint 1)
+  where
+    fixPoint :: Word8 -> Word8
+    fixPoint !n
+        | maxN n <= n = n
+        | n == maxBound = n
+        | otherwise = fixPoint (n + 1)
+      where
+        maxN :: Word8 -> Word8
+        maxN = maximumNumberOfInputs coinselOpts
diff --git a/lib/core/test/unit/Cardano/Wallet/Primitive/CoinSelection/MigrationSpec.hs b/lib/core/test/unit/Cardano/Wallet/Primitive/CoinSelection/MigrationSpec.hs
@@ -9,7 +9,7 @@ import Prelude
 import Cardano.Wallet.Primitive.CoinSelection
     ( CoinSelection (..), changeBalance, inputBalance )
 import Cardano.Wallet.Primitive.CoinSelection.Migration
-    ( selectCoinsForMigration )
+    ( idealBatchSize, selectCoinsForMigration )
 import Cardano.Wallet.Primitive.CoinSelectionSpec
     ()
 import Cardano.Wallet.Primitive.Fee
@@ -21,15 +21,21 @@ import Cardano.Wallet.Primitive.Types
 import Test.Hspec
     ( Spec, describe, it, shouldSatisfy )
 import Test.QuickCheck
-    ( conjoin, counterexample, property, withMaxSuccess, (===) )
+    ( conjoin, counterexample, label, property, withMaxSuccess, (===) )
 
 import qualified Data.Map as Map
 import qualified Data.Set as Set
 
 spec :: Spec
 spec = do
 
-    describe "Coin selection for migration PATATE" $ do
+    describe "idealBatchSize" $ do
+        it "Eventually converge for decreasing functions" $ do
+            property $ \coinselOpts -> do
+                let batchSize = idealBatchSize coinselOpts
+                label (show batchSize) True
+
+    describe "selectCoinsForMigration" $ do
 
         it "No coin selection has ouputs" $
             property $ withMaxSuccess 1000 $ \feeOpts batchSize utxo -> do

diff --git a/lib/core/test/unit/Cardano/Wallet/Primitive/CoinSelectionSpec.hs b/lib/core/test/unit/Cardano/Wallet/Primitive/CoinSelectionSpec.hs
@@ -62,6 +62,7 @@ import Test.QuickCheck
     , checkCoverageWith
     , choose
     , cover
+    , elements
     , generate
     , oneof
     , scale
@@ -206,6 +207,22 @@ coinSelectionUnitTest run lbl expected (CoinSelectionFixture n fn utxoF outsF) =
 
 deriving instance Arbitrary a => Arbitrary (ShowFmt a)
 
+instance Arbitrary (CoinSelectionOptions e) where
+    arbitrary = do
+        -- NOTE Functions have to be decreasing functions
+        fn <- elements
+            [ (maxBound -)
+            , \x ->
+                if x > maxBound `div` 2
+                    then maxBound
+                    else maxBound - (2 * x)
+            , const 42
+            ]
+        pure $ CoinSelectionOptions fn (const (pure ()))
+
+instance Show (CoinSelectionOptions e) where
+    show _ = "CoinSelectionOptions"
+
 instance Arbitrary a => Arbitrary (NonEmpty a) where
     shrink xs = catMaybes (NE.nonEmpty <$> shrink (NE.toList xs))
     arbitrary = do