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module Huffman |
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open System |
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open System.IO |
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type bit = bool |
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type path = bit list |
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type BinaryTreeNode = |
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| Leaf of byte * frequency:int |
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| Branch of left:BinaryTreeNode option * right:BinaryTreeNode option * frequency:int |
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member __.Switch(b:bit) = |
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match __ with |
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| Branch (_, right, _) when b -> right |
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| Branch (left, _, _) when not b-> left |
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| _ -> None |
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static member Empty = Leaf(0uy,0) |
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member private __.cost = |
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lazy |
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match __ with |
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| Leaf (_, f) -> f |
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| Branch(_,_,f) -> f |
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member __.Cost() = __.cost.Value |
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type BitWriter(stream:Stream) = |
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let buffer = ref 0uy |
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let len = ref 0 |
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let flush() = |
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while !len < 8 do |
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buffer := !buffer <<< 1 |
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buffer := !buffer ||| 0uy |
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len := !len + 1 |
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stream.WriteByte(!buffer) |
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stream.Flush() |
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buffer := 0uy |
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len := 0 |
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let mustFlush() = |
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!len >= 8 |
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member __.Flush() = |
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if mustFlush() then flush() |
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member __.Close() = |
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if !len > 0 then flush() |
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member __.Write(b:bit) = |
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let v = if b then 1uy else 0uy |
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buffer := ((!buffer) <<< 1) ||| v |
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len := !len + 1 |
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__.Flush() |
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member __.Write(bits:bit list) = |
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for b in bits do __.Write b |
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interface IDisposable with |
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member __.Dispose() = |
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__.Close() |
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type BitReader(stream:Stream) = |
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let buffer = ref 0uy |
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let len = ref 0 |
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let position = ref 0L |
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let loadBuffer() = |
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if stream.Position >= stream.Length |
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then buffer := 0uy |
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len := 8 |
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let by = stream.ReadByte() |
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if by = -1 |
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then buffer := 0uy |
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buffer := byte by |
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let readBit() = |
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len := !len - 1 |
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let mask = 1 <<< !len |
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let v = !buffer &&& (byte mask) |
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position := !position + 1L |
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v >= 1uy |
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let peekBit() = |
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let mask = 1 <<< (!len - 1) |
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let v = !buffer &&& (byte mask) |
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v >= 1uy |
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member __.End with get() = stream.Position >= stream.Length && !len <= 0 |
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member __.Position with get() = position |
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member __.Read() = |
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if __.End |
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then None |
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else |
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if !len <= 0 |
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then loadBuffer() |
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Some (readBit()) |
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member __.Peek() = |
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if __.End |
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then None |
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else |
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if !len <= 0 |
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then loadBuffer() |
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Some (peekBit()) |
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type BinaryTree (root:BinaryTreeNode) = |
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member __.Root with get() = root |
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member __.GetPath (data:byte) = |
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let rec scan (node:BinaryTreeNode) (d:byte) (p:path) = |
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let scanBranch (left:BinaryTreeNode option) (right:BinaryTreeNode option) (cp:path) = |
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let scanChildren parent v = |
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match parent with |
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| Some(Leaf(l,f)) -> scan (Leaf(l,f)) d (cp @ [v]) |
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| Some n -> scan n d (cp @ [v]) |
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| None -> None |
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scanChildren left false |
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|> function |
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| Some r -> Some r |
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| None -> scanChildren right true |
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match node with |
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| Leaf (b,_) when b = data -> Some p |
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| Leaf _ -> None |
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| Branch (left, right, _) -> scanBranch left right p |
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scan root data [] |
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member __.GetByte(p:path) = |
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let rec loop (bits:path) (current:BinaryTreeNode) = |
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match bits, current with |
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| true :: tail, Branch(_, Some r, _) -> loop tail r |
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| false :: tail, Branch(Some l,_, _) -> loop tail l |
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| _, Leaf(d, _) -> d |
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| _ -> failwith "invalid path" |
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loop p root |
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let buildTree (frequencies: (byte*int) list) = |
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let sort (tree:BinaryTreeNode list) = |
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tree |> List.sortBy (fun i -> i.Cost()) |
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let rec loop (tree:BinaryTreeNode list) = |
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match sort tree with |
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| left::right::[] -> |
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Branch(Some left, Some right, left.Cost() + right.Cost()) |
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| left::right::tail -> |
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let branch = Branch(Some left, Some right, left.Cost() + right.Cost()) |
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loop (branch :: tail) |
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| [single] -> single |
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| [] -> failwith "invalid operation" |
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frequencies |
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|> Seq.map Leaf |
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|> List.ofSeq |
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|> loop |
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|> BinaryTree |
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let getFrequencies (l:byte list) = |
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l |> Seq.groupBy(fun c -> c) |
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|> Seq.map (fun (c,l) -> c, (List.ofSeq l).Length) |
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|> Seq.toList |
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let getFrequencies' (stream:Stream) = |
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let rec loop (acc:(byte*int) list) = |
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let i = stream.ReadByte() |
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if i < 0 |
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then acc |
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else |
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let b = byte i |
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match acc |> List.tryFind(fun (v,_) -> v = b) with |
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| Some (_,c) -> |
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acc |
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|> List.filter(fun (v,_) -> v <> b) |
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|> List.append [(b, (c+1))] |
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| None -> acc |> List.append [(b, 1)] |
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|> loop |
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stream.Position <- 0L |
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let f = loop [] |
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stream.Position <- 0L |
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f |
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let serializeTree stream (frequencies: (byte*int) list) = |
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let binaryWriter = new BinaryWriter(stream) |
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binaryWriter.Write(frequencies.Length) |
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for b,c in frequencies do |
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binaryWriter.Write b |
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binaryWriter.Write c |
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binaryWriter.Flush() |
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stream.Flush() |
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let deserializeFrequencies stream = |
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let binaryReader = new BinaryReader(stream) |
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let count = binaryReader.ReadInt32() |
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[0..(count-1)] |
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|> Seq.map (fun _ -> binaryReader.ReadByte(), binaryReader.ReadInt32()) |
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|> Seq.toList |
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let deserializeTree stream = |
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stream |> deserializeFrequencies |> buildTree |
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let compress (output:Stream) (bytes:byte list) = |
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use writer = new BitWriter(output) |
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let frequencies = getFrequencies bytes |
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serializeTree output frequencies |
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let tree = buildTree frequencies |
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for b in bytes do |
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let p = tree.GetPath b |
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match p with |
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| Some bits -> bits |> List.iter writer.Write |
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| None -> raise <| ArithmeticException "compression failed" |
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writer.Close() |
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let compressStream (output:Stream) (input:Stream) = |
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use writer = new BitWriter(output) |
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let frequencies = getFrequencies' input |
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serializeTree output frequencies |
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let tree = buildTree frequencies |
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while input.Position < input.Length do |
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let b = byte <| input.ReadByte() |
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let p = tree.GetPath b |
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match p with |
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| Some bits -> bits |> List.iter writer.Write |
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| None -> raise <| ArithmeticException "compression failed" |
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writer.Close() |
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let rec readPath (reader:BitReader) (node:BinaryTreeNode) acc = |
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let sb = reader.Peek() |
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let next() = reader.Read() |> ignore |
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match reader.End, sb, node with |
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| false, Some b, Branch(Some(Leaf(d,_)), _, _) when not b -> |
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next(); Some d |
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| false, Some b, Branch(Some l, _, _) when not b -> |
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next() |
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readPath reader l acc |
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| false, Some b, Branch(_, Some(Leaf(d,_)), _) when b -> |
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next(); Some d |
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| false, Some b, Branch(_, Some r, _) when b -> |
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next() |
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readPath reader r acc |
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| false, Some true, Leaf(d,_) -> next(); Some d |
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| false, Some false, Leaf(d,_) -> Some d |
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| true, _, _ -> None |
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| _ -> failwith "corrupted stream" |
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let decompress stream = |
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let tree = deserializeTree stream |
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let reader = BitReader stream |
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seq { |
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while not reader.End do |
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match readPath reader tree.Root [] with |
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| Some b -> yield b |
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| None -> () |
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} |> Seq.toList |
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let decompressInStream stream (output:Stream) = |
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let tree = deserializeTree stream |
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let reader = BitReader stream |
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while not reader.End do |
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match readPath reader tree.Root [] with |
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| Some b -> |
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output.WriteByte b |
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| None -> () |
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output.Flush() |
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let strToBytes (s:string) = |
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s.ToCharArray() |
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|> Seq.map byte |
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|> Seq.toList |
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/Huffman.fs
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