ROOT   Reference Guide
MersenneTwisterEngine.cxx
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1// @(#)root/mathcore:$Id$
2// Authors: L. Moneta 8/2015
3
4/**********************************************************************
5 * *
6 * Copyright (c) 2015 , ROOT MathLib Team *
7 * *
8 * *
9 **********************************************************************/
10
11// implementation file of Mersenne-Twister engine
12//
13//
14// Created by: Lorenzo Moneta : Tue 4 Aug 2015
15//
16//
18
19
20namespace ROOT {
21namespace Math {
22
23 /// set the seed x
24 void MersenneTwisterEngine::SetSeed(unsigned int seed) {
25 fCount624 = 624;
26 if (seed > 0) {
27 fMt[0] = seed;
28
29 // use multipliers from Knuth's "Art of Computer Programming" Vol. 2, 3rd Ed. p.106
30 for(int i=1; i<624; i++) {
31 fMt[i] = (1812433253 * ( fMt[i-1] ^ ( fMt[i-1] >> 30)) + i );
32 }
33 }
34 }
35
36 /// generate a random double number
38
39
40 uint32_t y;
41
42 const int kM = 397;
43 const int kN = 624;
44 const uint32_t kTemperingMaskB = 0x9d2c5680;
45 const uint32_t kTemperingMaskC = 0xefc60000;
46 const uint32_t kUpperMask = 0x80000000;
47 const uint32_t kLowerMask = 0x7fffffff;
48 const uint32_t kMatrixA = 0x9908b0df;
49
50 if (fCount624 >= kN) {
51 int i;
52
53 for (i=0; i < kN-kM; i++) {
55 fMt[i] = fMt[i+kM] ^ (y >> 1) ^ ((y & 0x1) ? kMatrixA : 0x0);
56 }
57
58 for ( ; i < kN-1 ; i++) {
60 fMt[i] = fMt[i+kM-kN] ^ (y >> 1) ^ ((y & 0x1) ? kMatrixA : 0x0);
61 }
62
64 fMt[kN-1] = fMt[kM-1] ^ (y >> 1) ^ ((y & 0x1) ? kMatrixA : 0x0);
65 fCount624 = 0;
66 }
67
68 y = fMt[fCount624++];
69 y ^= (y >> 11);
70 y ^= ((y << 7 ) & kTemperingMaskB );
71 y ^= ((y << 15) & kTemperingMaskC );
72 y ^= (y >> 18);
73
74 // 2.3283064365386963e-10 == 1./(max<UINt_t>+1) -> then returned value cannot be = 1.0
75 if (y) return ( (double) y * 2.3283064365386963e-10); // * Power(2,-32)
76 return Rndm_impl();
77
78 }
79
80 } // namespace Math
81} // namespace ROOT
void SetSeed(Result_t seed)
set the seed x
double Rndm_impl()
generate a random double number
Double_t y[n]
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