Feature idea: equalv

[reynir]

I found that I wanted to compare two lists of cstructs if they each combined contained the same bytes. It can easily but inefficiently be implemented using Cstruct.equal (Cstruct.concat xs) (Cstruct.concat ys). Implementing it more efficiently is less straight forward.

  let cstruct_equalv a b =
    let rec loop a b =
      match a, b with
      | [], [] -> true
      | [], _ | _, [] -> false
      | a :: a', b :: b' ->
        let l = min (Cstruct.length a) (Cstruct.length b) in
        let remainder x xs =
          if Cstruct.length x > l then
            Cstruct.sub x l (Cstruct.length x - l) :: xs
          else
            xs
        in
        Cstruct.equal (Cstruct.sub a 0 l) (Cstruct.sub b 0 l) &&
        loop (remainder a a') (remainder b b')
    in
    Cstruct.lenv a = Cstruct.lenv b &&
    loop a b

It may be a slippery slope to add more and more *v functions.

[avsm]

We could define a Cstruct.List module and put the various (len, equal, compare) functions in there for efficient operations over lists of Cstructs.