HP.thy

(*
   Copyright 2016 Yoichi Hirai

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
*)

theory HP

imports Main "~~/src/HOL/Word/Word"

begin

type_synonym byte = "8 word"
type_synonym nibble = "4 word"

fun "HP_f" :: "bool \<Rightarrow> byte"
where
  "HP_f True  = 2"
| "HP_f False = 0"

value "HP_f False"

value "word_rcat"

fun "HP_raw" :: "nibble list \<Rightarrow> byte list"
where
  "HP_raw [] = []"
| "HP_raw [x] = [ucast x]"
| "HP_raw (a # b # rest) = (word_rcat [a, b]) # HP_raw rest"

definition "HP" :: "nibble list \<Rightarrow> bool \<Rightarrow> byte list"
where
"HP lst t =
  (if even (length lst) then
  (16 * (HP_f t)) # HP_raw lst
  else
  (16 * (1 + HP_f t) + ucast (hd lst)) # HP_raw (tl lst))
  "

value "HP [0, 1, 2, 3] True"

end