From 94ddb362ced51bd750cc01532ba50139e0abe739 Mon Sep 17 00:00:00 2001
From: tomsmeding <tom.smeding@gmail.com>
Date: Fri, 20 Dec 2019 11:46:45 +0100
Subject: Day 18 part 1

---
 2019/SmallIntSet.hs | 54 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 54 insertions(+)
 create mode 100644 2019/SmallIntSet.hs

(limited to '2019/SmallIntSet.hs')

diff --git a/2019/SmallIntSet.hs b/2019/SmallIntSet.hs
new file mode 100644
index 0000000..182b850
--- /dev/null
+++ b/2019/SmallIntSet.hs
@@ -0,0 +1,54 @@
+module SmallIntSet (
+    SmallIntSet,
+    toList, fromList, size, empty, singleton, insert, member, notMember, union, (\\)
+) where
+
+import Data.Bits
+import Data.List (intercalate)
+
+
+nBits :: Int
+nBits = finiteBitSize (undefined :: Int)
+
+newtype SmallIntSet = SmallIntSet Int
+  deriving (Eq, Ord)
+
+instance Show SmallIntSet where
+    show set = "{" ++ intercalate "," (map show (toList set)) ++ "}"
+
+instance Semigroup SmallIntSet where
+    s1 <> s2 = union s1 s2
+
+toList :: SmallIntSet -> [Int]
+toList (SmallIntSet bm) = [n | n <- [0..nBits-1], testBit bm n]
+
+fromList :: [Int] -> SmallIntSet
+fromList = foldr insert empty
+
+size :: SmallIntSet -> Int
+size (SmallIntSet bm) = popCount bm
+
+empty :: SmallIntSet
+empty = SmallIntSet 0
+
+singleton :: Int -> SmallIntSet
+singleton n = checkValid n `seq` SmallIntSet (1 `shiftL` n)
+
+insert :: Int -> SmallIntSet -> SmallIntSet
+insert n (SmallIntSet bm) = checkValid n `seq` SmallIntSet (bm .|. (1 `shiftL` n))
+
+member :: Int -> SmallIntSet -> Bool
+member n (SmallIntSet bm) = checkValid n `seq` (bm .&. (1 `shiftL` n)) /= 0
+
+notMember :: Int -> SmallIntSet -> Bool
+notMember n (SmallIntSet bm) = checkValid n `seq` (bm .&. (1 `shiftL` n)) == 0
+
+union :: SmallIntSet -> SmallIntSet -> SmallIntSet
+union (SmallIntSet b1) (SmallIntSet b2) = SmallIntSet (b1 .|. b2)
+
+(\\) :: SmallIntSet -> SmallIntSet -> SmallIntSet
+SmallIntSet b1 \\ SmallIntSet b2 = SmallIntSet (b1 .&. complement b2)
+
+checkValid :: Int -> Bool
+checkValid n | 0 <= n, n < nBits = True
+             | otherwise = error $ "SmallIntSet bounds violated with " ++ show n
-- 
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