std::subtract_with_carry_engine<UIntType,w,s,r>::subtract_with_carry_engine - cppreference.com (original) (raw)

Constructs the pseudo-random number engine.

1. The default constructor.

• If the default-constructed engine is of type std::ranlux24_base, the 10000th consecutive invocation of it produces the value 7937952.
• If the default-constructed engine is of type std::ranlux48_base, the 10000th consecutive invocation of it produces the value 61839128582725.

1. Constructs the engine with a seed value value. The sequence X of the engine's initial state is determined as follows:

1. Constructs a std::linear_congruential_engine<std::uint_least32_t, 40014u, 0u, 2147483563u> object e with argument value == 0u ? default_seed : static_cast<std::uint_least32_t>(value % 2147483563u).

2. Let n be std::size_t(w / 32) + 1.

3. Sets the values of \(\scriptsize X_{-r} \)X-r, ..., \(\scriptsize X_{-1} \)X-1, in that order. Each value \(\scriptsize X_i \)Xi is set as specified below:

4. Successively calls e for n times, the return values are denoted as \(\scriptsize z_0 \)z0 ... \(\scriptsize z_{n-1} \)zn-1.

5. Sets \(\scriptsize X_i \)Xi to \(\scriptsize (\sum^{n-1}_{j=0} z_j \cdot 2^{32j}) \mod m \)(∑n-1
   j=0 zj·232j
   ) mod m.

If \(\scriptsize X_{-1} \)X-1 is ​0​, sets the carry value c of the engine's initial state to 1. Otherwise, sets c to ​0​.

1. Constructs the engine with a seed sequence seq. Given std::size_t(w / 32) + 1 as k, the sequence X of the engine's initial state is determined as follows:

1. Creates an invented array object a of length r * k.
2. Calls seq.generate(a + 0, a + r * k).
3. For each integer i in [-r, -1], sets \(\scriptsize X_{i} \)Xi to \(\scriptsize (\sum^{k-1}_{j=0} a_{k(i+r)+j} \cdot 2^{32j}) \mod m \)(∑k-1
   j=0 ak(i+r)+j·232j
   ) mod m.

If \(\scriptsize X_{-1} \)X-1 is ​0​, sets the carry value c of the engine's initial state to 1. Otherwise, sets c to ​0​.

This overload participates in overload resolution only if SeedSeq meets the requirements of SeedSequence.

1. The copy constructor. Upon construction, *this == other is true.

[edit] Parameters

[edit] Complexity

1,2) (std::size_t(w / 32) + 1) * r invocations of e.

1. Same as the complexity of the seq.generate call.

2. \(\scriptsize O(r) \)O(r).

[edit] Exceptions

1. If SeedSeq is not std::seed_seq, throws the exceptions thrown by the seq.generate call.

[edit] Example

#include #include   int main() { std::ranlux24_base gen24; // overload (1) std::ranlux48_base gen48; // overload (1) gen24.discard(10000 - 1); gen48.discard(10000 - 1); assert(gen24() == 7'937'952); assert(gen48() == 61'839'128'582'725); }

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[edit] See also

| | sets the current state of the engine (public member function) [edit] | | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |