From 9aabb53bfda096dafebfddaab8df274d82ac01b4 Mon Sep 17 00:00:00 2001
From: Tom Smeding <tom.smeding@gmail.com>
Date: Wed, 8 Aug 2018 23:17:38 +0200
Subject: Unsafe array operations in FSu

Another 15% faster on suvh.txt, for a total of 32%
---
 hsolve/FSu.hs | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

diff --git a/hsolve/FSu.hs b/hsolve/FSu.hs
index 1d0eea3..dc0f4c6 100644
--- a/hsolve/FSu.hs
+++ b/hsolve/FSu.hs
@@ -3,6 +3,7 @@ module FSu(solve) where
 
 import Control.Monad
 import Control.Monad.ST
+import Data.Array.Base (unsafeRead, unsafeWrite)
 import Data.Array.ST
 import Data.STRef
 
@@ -36,7 +37,7 @@ solveAt arr !i st = do
             res <- obtainResult arr
             modifySTRef' (stateResults st) (res:)
         else do
-            v <- readArray arr i
+            v <- unsafeRead arr i
             if v /= (-1)
             then solveAt arr (i+1) st
             else do
@@ -46,9 +47,9 @@ solveAt arr !i st = do
 tryAll :: Arr s Value -> Index -> [Value] -> State s -> ST s ()
 tryAll _ _ [] _ = return ()
 tryAll arr !i (v:vs) st = do
-    writeArray arr i v
+    unsafeWrite arr i v
     solveAt arr (i+1) st
-    writeArray arr i (-1)
+    unsafeWrite arr i (-1)
     tryAll arr i vs st
 
 -- assumes the considered position is empty
@@ -65,18 +66,18 @@ getPoss arr i st = do
 
     goRow :: Int -> Int -> ST s ()
     goRow _ 9 = return ()
-    goRow r j = readArray arr (9 * r + j) >>= \v ->
-        when (v /= (-1)) (writeArray mark v False) >> goRow r (j+1)
+    goRow r j = unsafeRead arr (9 * r + j) >>= \v ->
+        when (v /= (-1)) (unsafeWrite mark v False) >> goRow r (j+1)
 
     goCol :: Int -> Int -> ST s ()
     goCol _ 9 = return ()
-    goCol c j = readArray arr (9 * j + c) >>= \v ->
-        when (v /= (-1)) (writeArray mark v False) >> goCol c (j+1)
+    goCol c j = unsafeRead arr (9 * j + c) >>= \v ->
+        when (v /= (-1)) (unsafeWrite mark v False) >> goCol c (j+1)
 
     goBlock :: Int -> Int -> ST s ()
     goBlock _ 9 = return ()
-    goBlock b j = readArray arr (b + 9 * (j `quot` 3) + j `rem` 3) >>= \v ->
-        when (v /= (-1)) (writeArray mark v False) >> goBlock b (j+1)
+    goBlock b j = unsafeRead arr (b + 9 * (j `quot` 3) + j `rem` 3) >>= \v ->
+        when (v /= (-1)) (unsafeWrite mark v False) >> goBlock b (j+1)
 
 isValid :: forall s. Arr s Value -> State s -> ST s Bool
 isValid arr st = do
@@ -115,14 +116,14 @@ indexSetNoDups arr set st = do
     applyInMark :: [Int] -> ST s Bool
     applyInMark [] = return True
     applyInMark (i:is) =
-        readArray arr i >>= \v ->
+        unsafeRead arr i >>= \v ->
             if v == (-1)
             then applyInMark is
             else do
-                b <- readArray mark v
+                b <- unsafeRead mark v
                 if b
                 then return False
-                else writeArray mark v True >> applyInMark is
+                else unsafeWrite mark v True >> applyInMark is
 
 fillArrayBool :: Arr s Bool -> Int -> Int -> Bool -> ST s ()
 fillArrayBool arr !i1 !i2 v
-- 
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