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From: DINARICH@eldi.epfl.ch (Mirko Dinarich)
Newsgroups: comp.sys.apple2
Subject: Re: TML Pascal II...
Message-ID: <3335@disuns2.epfl.ch>
Date: 3 Mar 92 11:41:55 GMT
References: <1992Mar3.021749.11353@nuscc.nus.sg>
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In-Reply-To: ltchean@iss.nus.sg's message of 3 Mar 92 02:17:49 GMT

In <1992Mar3.021749.11353@nuscc.nus.sg> ltchean@iss.nus.sg writes:

> So without this operator, the new algorithm is sooooo much slower. Or somebody
> else can provide me with a short algorithm that can handle Power(x, y: integer): longInt efficiently?

Hello

A friend of mine writes this function:

FUNCTION Power (x : LONGINT;
                y : INTEGER) : LONGINT;

  VAR r : LONGINT;

  BEGIN (* Power *)
    r := 1;

    WHILE y>0 DO
      BEGIN
        IF odd(y) THEN
          r := r * x;     (* or Mult (r, x) *)

        y := y DIV 2;
        x := x * x        (* or Mult (x, x) *)
      END;

    Power := r
  END; (* Power *)


If the multiplication function is slow you can utilise this one:
----------------------------------------------------------------

FUNCTION Mult (x : LONGINT;
               y : LONGINT) : LONGINT;

  VAR r    : LONGINT;
      sign : BOOLEAN;

  BEGIN (* Mult *)
    r := 0;

    sign := y<0;

    IF sign THEN
      y := -y;

    WHILE y>0 DO
      BEGIN
        IF odd(y) THEN
          r := r + x;

        y := y DIV 2;
        x := x * 2        (* or x + x if faster *)
      END;

    IF sign THEN
      Mult := -r
    ELSE
      Mult := r
  END; (* Mult *)


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