(* random.sml *)

(* Copyright (C) 2007 Alley Stoughton

   This file is part of crypto, a cryptogram encoder/decoder.  See the
   file COPYING.txt for copying and usage restrictions *)

(* a structure for generating random numbers *)

(* will only compile if IntInf = LargeInt *)

structure Random :> RANDOM =
struct

(* currently, Word31.word *)

type seed = Rand.rand

fun makeFromTime() =
      let val secs : IntInf.int = Time.toSeconds(Time.now())
          val randMin           = Word31.toLargeInt Rand.randMin
          val randMax           = Word31.toLargeInt Rand.randMax
      in Word31.fromLargeInt(randMin + secs mod (randMax - randMin + 1)) end
  
exception BadRange

fun getInRange(seed, m, n) =
      if m > n
      then raise BadRange
      else let val seed           = Rand.random seed
               val m : IntInf.int = LargeInt.fromInt m
               val n              = LargeInt.fromInt n
               val i              = Word31.toLargeInt seed mod (n - m + 1) + m
           in (seed, LargeInt.toInt i) end

end;