Initial commit

CipherSuite/FitnessAnalyser.fs

@@ -0,0 +1,83 @@
+namespace CipherSuite
+
+open System
+
+type Fitness =
+    private
+        {
+            Quadruplets : Arr4D<int>
+            Total : int
+        }
+
+[<RequireQualifiedAccess>]
+module Fitness =
+
+    let inline private toIndex (c : char) : int = int (System.Char.ToUpper c) - 65
+
+#if DEBUG
+    let fromEmbedded () : Fitness =
+        let frequencies = Arr4D.zeroCreate<_> 26 26 26 26
+#else
+
+    let allocate () =
+        Array.zeroCreate<int> (26 * 26 * 26 * 26)
+
+    /// Pass in a pointer to an array of length 26*26*26*26, e.g. a pointer to
+    /// the output of `allocate`.
+    let fromEmbedded (arr : nativeptr<int>) : Fitness =
+        let frequencies = Arr4D.zeroCreate<_> arr 26 26 26 26
+#endif
+        let tetragraphs = Assembly.loadResource "CipherSuite.tetragraphs.txt"
+
+        let mutable total = 0
+
+        for line in tetragraphs do
+            if line.[0] <> '#' then
+                let line = line.AsSpan ()
+                let i = Int32.Parse (line.Slice (line.IndexOf (' ') + 1))
+                total <- total + i
+                let w = toIndex line.[0]
+                let x = toIndex line.[1]
+                let y = toIndex line.[2]
+                let z = toIndex line.[3]
+
+                if w < 0 || x < 0 || y < 0 || z < 0 then
+                    failwith "negative"
+
+                if w > 25 || x > 25 || y > 25 || z > 25 then
+                    failwith "too big"
+
+                Arr4D.set frequencies w x y z i
+
+        {
+            Quadruplets = frequencies
+            Total = total
+        }
+
+    /// Assumes the input is characters 0..25, where "a" is 0.
+    /// This fitness can meaningfully be compared across strings
+    /// with different lengths.
+    let get' (s : int[]) (f : Fitness) : float =
+        let mutable score = 0
+
+        for j = 0 to s.Length - 4 do
+            let first = s.[j]
+            let second = s.[j + 1]
+            let third = s.[j + 2]
+            let fourth = s.[j + 3]
+
+            score <- score + Arr4D.get f.Quadruplets first second third fourth
+
+        float score / float s.Length
+
+    let get (s : string) (f : Fitness) : float =
+        let s =
+            s.ToUpper().ToCharArray ()
+            |> Array.choose (fun c ->
+                if 'A' <= c && c <= 'Z' then
+                    Some (int c - int 'A')
+                else
+                    None
+            )
+
+        get' s f