梅森旋轉法(也有翻譯爲馬特賽特旋轉算法)產生的僞隨機數比線性同餘法要好。產生隨機數的速度快、週期長,可達到2^19937-1,且具有623維均勻分佈的性質,對於一般的應用來說,足夠大了,序列關聯比較小,能通過很多隨機性測試。現在很多編程語言都默認用梅森旋轉法來提供僞隨機數比如c++從11開始加入了梅森旋轉法,但delphi一直都是用的線性同於法,在xe10.3還是這樣的:
//Random integer, implemented as a deterministic linear congruential generator
// with 134775813 as a and 1 as c.
在一個日本網站上找到了現成的梅森旋轉法Pascal代碼,直接保存爲pas文件即可使用。
使用方法:
procedure TForm1.FormCreate(Sender: TObject);
begin
Randomize; //原隨機數初始化
InitMT(Random(9999999)); //用線性同餘法生成的隨機數來初始化梅森旋轉法
end;
procedure TForm1.Button1Click(Sender: TObject);
begin
memo1.Lines.Add(IRanMT.ToString); //獲取一個梅森旋轉隨機數
end;
梅森旋轉法單元代碼
{ ****************************************************************** Mersenne Twister Random Number Generator for pascal ******************************************************************} unit uranmt; interface procedure InitMT(Seed : LongInt); { Initializes MT generator with a seed } procedure InitMTbyArray(InitKey : array of LongInt; KeyLength : Word); { Initialize MT generator with an array InitKey[0..(KeyLength - 1)] } function IRanMT : cardinal; { Generates a Random number } implementation const N = 624; M = 397; MATRIX_A = $9908b0df; { constant vector a } UPPER_MASK = $80000000; { most significant w-r bits } LOWER_MASK = $7fffffff; { least significant r bits } mag01 : array[0..1] of Cardinal{LongInt} = (0, MATRIX_A); var mt : array[0..(N-1)] of Cardinal{LongInt}; { the array for the state vector } mti : Word; { mti == N+1 means mt[N] is not initialized } procedure InitMT(Seed : LongInt); var i : Word; begin mt[0] := Seed and $ffffffff; for i := 1 to N-1 do begin mt[i] := (1812433253 * (mt[i-1] Xor (mt[i-1] shr 30)) + i); { See Knuth TAOCP Vol2. 3rd Ed. P.106 For multiplier. In the previous versions, MSBs of the seed affect only MSBs of the array mt[]. 2002/01/09 modified by Makoto Matsumoto } mt[i] := mt[i] and $ffffffff; { For >32 Bit machines } end; mti := N; end; procedure InitMTbyArray(InitKey : array of LongInt; KeyLength : Word); var i, j, k, k1 : Word; begin InitMT(19650218); i := 1; j := 0; if N > KeyLength then k1 := N else k1 := KeyLength; for k := k1 downto 1 do begin mt[i] := (mt[i] Xor ((mt[i-1] Xor (mt[i-1] shr 30)) * 1664525)) + InitKey[j] + j; { non linear } mt[i] := mt[i] and $ffffffff; { for WORDSIZE > 32 machines } i := i + 1; j := j + 1; if i >= N then begin mt[0] := mt[N-1]; i := 1; end; if j >= KeyLength then j := 0; end; for k := N-1 downto 1 do begin mt[i] := (mt[i] Xor ((mt[i-1] Xor (mt[i-1] shr 30)) * 1566083941)) - i; { non linear } mt[i] := mt[i] and $ffffffff; { for WORDSIZE > 32 machines } i := i + 1; if i >= N then begin mt[0] := mt[N-1]; i := 1; end; end; mt[0] := $80000000; { MSB is 1; assuring non-zero initial array } end; function IRanMT : cardinal; var y : cardinal; k : Word; begin if mti >= N then { generate N words at one Time } begin { If IRanMT() has not been called, a default initial seed is used } if mti = N + 1 then InitMT(5489); for k := 0 to (N-M)-1 do begin y := (mt[k] and UPPER_MASK) or (mt[k+1] and LOWER_MASK); mt[k] := mt[k+M] xor (y shr 1) xor mag01[y and $1]; end; for k := (N-M) to (N-2) do begin y := (mt[k] and UPPER_MASK) or (mt[k+1] and LOWER_MASK); mt[k] := mt[k - (N - M)] xor (y shr 1) xor mag01[y and $1]; end; y := (mt[N-1] and UPPER_MASK) or (mt[0] and LOWER_MASK); mt[N-1] := mt[M-1] xor (y shr 1) xor mag01[y and $1]; mti := 0; end; y := mt[mti]; mti := mti + 1; { Tempering } y := y xor (y shr 11); y := y xor ((y shl 7) and $9d2c5680); y := y xor ((y shl 15) and $efc60000); y := y xor (y shr 18); IRanMT := y end; const init : array[0..3] of LongInt = ($123, $234, $345, $456); begin InitMTbyArray(init, 4); end. { ****************************************************************** Mersenne Twister Random Number Generator end ******************************************************************}
更多代碼可以在這日本網站看到:http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/VERSIONS/PASCAL/pascal.html