(*

 * Hedgewars, a free turn based strategy game

 * Copyright (c) 2004-2015 Andrey Korotaev <unC0Rr@gmail.com>

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

 * the Free Software Foundation; version 2 of the License

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

 *)

{$INCLUDE "options.inc"}

unit uRandom;

(*

 * This unit supplies platform-independent functions for getting various

 * pseudo-random values based on a shared seed.

 *

 * This is necessary for accomplishing pseudo-random behavior in the game

 * without causing a desynchronisation of different clients when playing over

 * a network.

 *)

interface

uses uFloat;

procedure SetRandomSeed(Seed: shortstring; dropAdditionalPart: boolean); // Sets the seed that should be used for generating pseudo-random values.

function  GetRandomf: hwFloat; // Returns a pseudo-random hwFloat.

function  GetRandom(m: LongWord): LongWord; inline; // Returns a positive pseudo-random integer smaller than m.

procedure AddRandomness(r: LongWord); inline;

function  rndSign(num: hwFloat): hwFloat; // Returns num with a random chance of having a inverted sign.

implementation

var cirbuf: array[0..63] of Longword;

    n: byte;

procedure AddRandomness(r: LongWord); inline;

begin

n:= (n + 1) and $3F;

   cirbuf[n]:= cirbuf[n] xor r;

end;

function GetNext: Longword; inline;

begin

    n:= (n + 1) and $3F;

    cirbuf[n]:=

           (cirbuf[(n + 40) and $3F] +           {n - 24 mod 64}

            cirbuf[(n +  9) and $3F])            {n - 55 mod 64}

            and $7FFFFFFF;                       {mod 2^31}

    GetNext:= cirbuf[n];

end;

procedure SetRandomSeed(Seed: shortstring; dropAdditionalPart: boolean);

var i, t, l: Longword;

begin

n:= 54;

if Length(Seed) > 54 then

    Seed:= copy(Seed, 1, 54); // not 55 to ensure we have odd numbers in cirbuf

t:= 0;

l:= Length(Seed);

while (t < l) and ((not dropAdditionalPart) or (Seed[t + 1] <> '|')) do

    begin

    cirbuf[t]:= byte(Seed[t + 1]);

    inc(t)

    end;

for i:= t to 54 do

    cirbuf[i]:= $A98765 + 68; // odd number

for i:= 0 to 1023 do

   GetNext;

end;

function GetRandomf: hwFloat;

begin

GetNext;

GetRandomf.isNegative:= false;

GetRandomf.QWordValue:= GetNext

end;

function GetRandom(m: LongWord): LongWord; inline;

begin

GetNext;

GetRandom:= GetNext mod m

end;

function rndSign(num: hwFloat): hwFloat;

begin

num.isNegative:= odd(GetNext);

rndSign:= num

end;

end.