hedgewars/uRandom.pas
author unc0rr
Sun, 02 Dec 2012 01:25:11 +0400
changeset 8178 8bd087478b48
parent 7579 51724c98a74f
child 8026 4a4f21070479
child 8912 78ea1839aac9
permissions -rw-r--r--
Fix QSettings problems: - Reopen file in ReadOnly mode if it was open in ReadWrite mode and is being read. This is needed for stupid QSettings which opens file in ReadWrite mode just to call readAll() on it. - Implement setSize(0)

(*
 * Hedgewars, a free turn based strategy game
 * Copyright (c) 2004-2012 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., 59 Temple Place - Suite 330, Boston, MA 02111-1307, 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); // Sets the seed that should be used for generating pseudo-random values.
function  GetRandomf: hwFloat; overload; // Returns a pseudo-random hwFloat.
function  GetRandom(m: LongWord): LongWord; overload; 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);
var i: Longword;
begin
n:= 54;

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

for i:= 0 to Pred(Length(Seed)) do
    cirbuf[i]:= byte(Seed[i + 1]);

for i:= Length(Seed) 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.