quantum_package/ocaml/Bitlist.ml

open Qptypes;;
open Core.Std;;

(*
Type for bits strings
=====================

list of Bits
*)

type t = Bit.t list

(* String representation *)
let to_string b = 
  let rec do_work accu = function
    | [] -> accu
    | head :: tail ->
      let new_accu = (Bit.to_string head) ^ accu
      in do_work new_accu tail
  in
  do_work "" b
;;

let of_string ?(zero='0') ?(one='1') s =
  String.to_list s
  |> List.rev_map ~f:( fun c ->
     if (c = zero) then Bit.Zero
     else if (c = one) then Bit.One
     else (failwith ("Error in string "^s) ) )
;;

(* Create a bit list from an int64 *)
let of_int64 i = 
  let rec do_work = function
  | 0L -> [ Bit.Zero ]
  | 1L -> [ Bit.One ]
  | i -> let b =
    match (Int64.bit_and i 1L ) with
    | 0L -> Bit.Zero
    | 1L -> Bit.One 
    | _ -> raise (Failure "i land 1 not in (0,1)")  
    in b:: ( do_work (Int64.shift_right_logical i 1) )
  in
  let adjust_length result = 
    let rec do_work accu = function
    | 64 -> accu 
    | i when i>64 -> raise (Failure "Error in of_int64 > 64")
    | i when i<0 -> raise (Failure "Error in of_int64 < 0")
    | i -> do_work (accu@[Bit.Zero])  (i+1)
    in
    do_work result (List.length result)
  in
  adjust_length (do_work i)
;;

(* Create an int64 from a bit list *)
let to_int64 l =
  assert ( (List.length l) <= 64) ;
  let rec do_work accu = function
    | [] -> accu
    | Bit.Zero::tail -> do_work Int64.(shift_left accu 1) tail
    | Bit.One::tail  -> do_work Int64.(bit_or one (shift_left accu 1)) tail
  in do_work Int64.zero (List.rev l)
;;

(* Create a bit list from a list of int64 *)
let of_int64_list l = 
  List.map ~f:of_int64 l 
  |> List.concat
;;

(* Compute n_int *)
let n_int_of_mo_tot_num mo_tot_num =
  let bit_kind_size = Bit_kind_size.to_int (Lazy.force Qpackage.bit_kind_size) in
  N_int_number.of_int ( (mo_tot_num-1)/bit_kind_size + 1 )
;;

(* Create a zero bit list *)
let zero n_int =
  let n_int = N_int_number.to_int n_int in
  let a = Array.init n_int (fun i-> 0L)  in
  of_int64_list ( Array.to_list a )
;;

(* Create an int64 list from a bit list *)
let to_int64_list l =
  let rec do_work accu buf counter = function
    | [] -> 
        begin
          match buf with
          | [] -> accu
          | _  -> (List.rev buf)::accu
        end
    | i::tail -> 
        if (counter < 64) then
          do_work accu (i::buf) (counter+1) tail
        else
          do_work ( (List.rev (i::buf))::accu) [] 1 tail
  in
  let l = do_work [] [] 1 l
  in
  List.rev_map ~f:to_int64 l
;;

(* Create a bit list from a list of MO indices *)
let of_mo_number_list n_int l = 
  let n_int = N_int_number.to_int n_int in
  let length = n_int*64 in
  let a = Array.create length (Bit.Zero) in
  List.iter ~f:(fun i-> a.((MO_number.to_int i)-1) <- Bit.One) l;
  Array.to_list a
;;

let to_mo_number_list l =
  let a = Array.of_list l in
  let mo_tot_num = MO_number.get_max () in
  let rec do_work accu = function
  | 0 -> accu
  | i ->
      begin
        let new_accu = 
        match a.(i-1) with
        | Bit.One  -> (MO_number.of_int ~max:mo_tot_num i)::accu 
        | Bit.Zero -> accu 
        in
        do_work new_accu (i-1)
      end
  in
  do_work [] (List.length l)
;;



(* logical operations on bit_list *)
let logical_operator2 op a b =
  let rec do_work_binary result a b = 
  match a, b with
  | [], [] -> result
  | [], _  | _ , [] -> raise (Failure "Lists should have same length")
  | (ha::ta), (hb::tb) -> 
    let newbit = op ha hb
    in  do_work_binary (newbit::result) ta tb
  in
  List.rev (do_work_binary [] a b)
;;

let logical_operator1 op b =
  let rec do_work_unary result b = 
  match b with
  | [] -> result
  | (hb::tb) -> 
    let newbit = op hb
    in  do_work_unary (newbit::result) tb
  in
  List.rev (do_work_unary [] b)
;;

let and_operator a b = logical_operator2 Bit.and_operator a b;;
let xor_operator a b = logical_operator2 Bit.xor_operator a b;;
let  or_operator a b = logical_operator2  Bit.or_operator a b;;
let not_operator   b = logical_operator1 Bit.not_operator   b ;;


let popcnt b = 
  let rec popcnt accu = function
    | [] -> accu
    | Bit.One::rest -> popcnt (accu+1) rest
    | Bit.Zero::rest -> popcnt (accu) rest
  in popcnt 0 b
;;