mersenne_twister Class
Generates a random sequence by the Mersenne twister algorithm. Retained for TR1 compatibility. Use mersenne_twister_engine Class instead.
template<class UIntType,
int W, int N, int M, int R,
UIntType A, int U, int S,
UIntType B, int T, UIntType C, int L>
class mersenne_twister {
public:
typedef mersenne_twister<UIntType, W, N, M, R,
P, U, S, B, T, C, L> _MyT;
typedef UIntType result_type;
static const int word_size = W;
static const int state_size = N;
static const int shift_size = M;
static const int mask_bits = R;
static const int UIntType parameter_a = A;
static const int output_u = U;
static const int output_s = S;
static const UIntType output_b = B;
static const int output_t = T;
static const UIntType output_c = C;
static const int output_l = L;
static const UIntType default_seed = 5489U;
explicit mersenne_twister(unsigned long x0 = default_seed);
mersenne_twister(const mersenne_twister& right);
mersenne_twister(mersenne_twister& right);
template<class Gen>
mersenne_twister(Gen& gen);
void seed(unsigned long x0 = default_seed);
template<class Gen>
void seed(Gen& gen);
result_type min() const;
result_type max() const;
result_type operator()();
};
Parameters
UIntType
The unsigned integer result type.W
The W engine parameter.N
The N engine parameter.R
The R engine parameter.A
The A engine parameter.U
The U engine parameter.S
The S engine parameter.B
The B engine parameter.T
The T engine parameter.C
The C engine parameter.L
The L engine parameter.
Remarks
The template class decribes a simple engine. It holds a large integral value with W * (N - 1) + R bits. It extracts W bits at a time from this large value, and when it has used all the bits it twists the large value by shifting and mixing the bits so that it has a new set of bits to extract from. The engine's state is the last N W-bit values used if operator() has been called at least N times, otherwise the M W-bit values that have been used and the last N - M values of the seed.
The template argument UIntType must be large enough to hold values up to 2W - 1. The values of the other template arguments must satisfy the following requirements:
0 < M <= N
0 <= R, U, S, T, L <= W
0 <= A, B, C <= 2W
W * (N - 1) + R must be a Mersenne prime
The generator twists the large value that it holds by executing the following code:
for (int i = 0; i < N; ++i)
{
temp = (x[i] & LMASK) << (W - 1) | (x[i + 1] & HMASK) >> 1;
if (temp & 1)
y[i] = (temp >> 1) ^ A ^ x[(i + R) % N];
else
y[i] = (temp >> 1) ^ x[(i + R) % N];
}
for (int i = 0; i < N; ++i)
x[i] = y[i];
where LMASK is an unsigned W-bit value with its low R bits set to 1 and the rest of its bits set to 0, and HMASK is the complement of LMASK.
The generator holds a current index idx initialized to 0. It extracts bits by executing the following code:
temp = x[idx++];
temp = temp ^ (temp >> U);
temp = temp ^ ((temp << S) & B);
temp = temp ^ ((temp << T) & C);
temp = temp ^ (temp >> L);
When idx reaches N the generator twists the stored value and sets idx back to 0.
Requirements
Header: <random>
Namespace: std
See Also
Reference
mersenne_twister::mersenne_twister