Day 23, part 2 - decompiled input by hand

.gitignore

@@ -1,5 +1,6 @@
 *
 !.gitignore
 !*.hs
+!*.c
 !*.js
 !*.txt

23.c

@@ -0,0 +1,37 @@
+#include <stdio.h>
+#include <stdbool.h>
+
+// unoptimized translation of input
+unsigned int naiveCount() {
+    unsigned short h = 0;
+    for (long b = 108100; b < 125100; b += 17) {
+        bool f = true;
+        for (long d = 2; d < b; d++) {
+            for (long e = 2; e < b; e++) {
+                if (d * e == b) {
+                    f = false;
+                }
+            }
+        }
+        h += !f
+    }
+    return h;
+}
+
+unsigned int count() {
+    unsigned short h = 0;
+    for (long b = 108100; b < 125100; b += 17) {
+        bool f = true;
+        for (unsigned short d = 2; f && d * d <= b; d++) {
+            if (b % d == 0) {
+                f = false;
+            }
+        }
+        h += !f;
+    }
+    return h;
+}
+
+int main() {
+    printf("%hu\n", count());
+}

23.hs

@@ -4,7 +4,6 @@ import Data.Char (ord)
 import Data.Sequence (Seq, fromList, index)
 import Data.Vector.Unboxed (Vector, (!), (//))
 import qualified Data.Vector.Unboxed as V (replicate)
-import Debug.Trace
 
 type Registers = Vector Int
 type Instruction = State -> State
@@ -29,10 +28,10 @@ getValue r v = case v of
     c -> r ! (getIndex c)
 
 app :: Function -> Value -> Value -> Instruction
-app (Function op fn) index value state@(State reg pos cnt) =
-    let i = getIndex index
+app (Function op fn) x y (State reg pos cnt) =
+    let i = getIndex x
     in  State {
-        registers = reg // [(i, reg ! i `fn` getValue reg value)],
+        registers = reg // [(i, reg ! i `fn` getValue reg y)],
         position  = pos + 1,
         countMul  = cnt + fromEnum (op == Mul)
     }
@@ -56,7 +55,7 @@ parseLine str =
             Nothing -> Register $ head s
 
 runInstructions :: Seq Instruction -> State -> Int
-runInstructions instructions state@(State reg pos cnt) =
+runInstructions instructions state@(State _ pos cnt) =
     if pos >= length instructions then cnt else
     let !nextState = instructions `index` pos $ state in runInstructions instructions nextState
 
@@ -64,4 +63,3 @@ main :: IO ()
 main = do
     instructions <- fromList . map parseLine . lines <$> readFile "23.txt"
     print $ runInstructions instructions (State (V.replicate 8 0) 0 0)
-    print $ runInstructions instructions (State (V.replicate 8 0 // [(0, 1)]) 0 0)

README.md

@@ -31,6 +31,7 @@ These are the runtimes of only one trial but the variances are fairly small and
 | 20  |  0.168      |
 | 21  |  4.013      |
 | 22  | 12.867      |  7.880
+| 23  |  0.274      |
 
 Problems that should be optimized further: 15