hedgewars/uRandom.pas
author nemo
Tue, 21 Aug 2018 15:11:28 -0400
branch0.9.24
changeset 13687 f60b3998ba56
parent 11827 4600dcb9db4f
child 13363 a79c1206bacd
permissions -rw-r--r--
only-stats should never create visual gears. and lua should never rely on visual gears being created. critical is just to help ensure ones important to gameplay don't get lost in fast-forward

(*
 * 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.