Hex string in F#

Hex.fs

(*
 * Copyright (c) 2017 Yuki Ono
 * Licensed under the MIT License.
 *)

open System
open System.Text

let proceduralEncode (bytes:byte[]): string =
    let sb = new StringBuilder(bytes.Length * 2)

    for b in bytes do
        sb.Append(b.ToString("x2")) |> ignore
    
    sb.ToString()

let fpEncode (bytes:byte[]): string =
    let byteToHex (b:byte) = b.ToString("x2")
    Array.map byteToHex bytes |> String.concat ""

let proceduralDecode (hex:string): byte[] =
    if hex.Length % 2 <> 0 then
        invalidArg "hex" "hex.Length is not even"
    
    let bytes = Array.create (hex.Length / 2) 0uy

    let mutable i = 0
    while i < bytes.Length do
        bytes.[i] <- Convert.ToByte(hex.Substring(i * 2, 2), 16)
        i <- i + 1

    bytes

let fpDecode (hex:string): byte[] =
    if hex.Length % 2 <> 0 then
        invalidArg "hex" "hex.Length is not even"

    let hexToByte (cs:char[]) = Convert.ToByte(new String(cs), 16)
    Seq.chunkBySize 2 hex |> Seq.map hexToByte |> Seq.toArray
        

[<EntryPoint>]
let main argv =
    let testBytes = [| 1uy; 2uy; 3uy; 4uy; 5uy; 11uy; 12uy; 13uy; 14uy; 15uy; 251uy; 252uy; 253uy; 254uy; 255uy |]
    printfn "%s" (proceduralEncode testBytes)
    printfn "%s" (fpEncode testBytes)

    let testHex = "01020304050b0c0d0e0ffbfcfdfeff"
    printfn "%s" (String.Join(",", (proceduralDecode testHex)))
    printfn "%s" (String.Join(",", (fpDecode testHex)))
    Console.Read() |> ignore
    0