std::linear...ntial_engine(3)

🌸 std::linear...ntial_engine(3) 🌸

okay bestie, this is the manual page for std::linear...ntial_engine(3) from the C++ Standard Libary — and yes, that’s literally how the header spells it, no cap 💀. We’re folding the manual name in right here so you know what universe we’re in: C++ Standard Library constructor territory, and it’s giving very specific seed energy ✨.

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🎀 NAME 🎀

• std::linear_congruential_engine::linear_congruential_engine — aka std::linear_congruential_engine::linear_congruential_engine. The NAME section really said “say it twice, it’s iconic” 💅.

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✨ Synopsis ✨

Here’s the synopsis exactly as the page lays it out, annotations and all — do not come for me about the formatting, I’m just the messenger 🫶:

linear_congruential_engine() :                                    (1)
(since C++11)
linear_congruential_engine(default_seed) {}
explicit linear_congruential_engine( result_type value );         (2)
(since C++11)
template< class SeedSeq >                                         (3)
(since C++11)
explicit linear_congruential_engine( SeedSeq& seq );
linear_congruential_engine( const linear_congruential_engine&
(since C++11)
other );                                                          (4)
(implicitly
                                                                        declared)

So what’s the vibe? It constructs the pseudo-random number engine. That’s the whole main-character job 💫.

1. The default constructor. That’s it. That’s the tweet ✨.
2. Constructs the engine with a seed value value. The engine’s initial state is determined like this:
   • If c % m == 0 and value % m == 0 are both true, the state is 1.
   • Otherwise, the state is value % m.
3. Constructs the engine with a seed sequence seq. Given std::size_t(std::log2(m) / 32) + 1 as k, the engine’s initial state is determined like this:
   1. Creates an invented array object a of length k + 3.
   2. Calls seq.generate(a + 0, a + k + 3).
   3. Let S be ((\sum^{k-1}_{j=0} a_{j+3} \cdot 2^{32j}) \mod m) — and the page also shows the rendered form (∑k-1 j=0 a j+3·232j ) mod m.
   4. If both c % m == 0 and S == 0 are true, sets the engine’s state to 1. Otherwise, sets the engine’s state to S.

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

4. The copy constructor. Upon construction, *this == other is true. Copy constructor ate, no crumbs 💅.

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🌈 Parameters 🌈

• value — seed value to use in the initialization of the internal state.
• seq — seed sequence to use in the initialization of the internal state.

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🦋 Complexity 🦋

1, 2) Constant.

3. Same as the complexity of the seq.generate call.
4. Constant.

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🩹 Defect reports 🩹

The following behavior-changing defect reports were applied retroactively to previously published C++ standards — yes, they went back and edited the lore 😭:

• DR: P0935R0
• Applied to: C++11
• Behavior as published: the default constructor was explicit
• Correct behavior: made implicit

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🔥 See also 🔥

• seed — sets the current state of the engine (C++11) (public member function).

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source/version: cppreference.com · date: 2024.06.10 · page stamp: std::linear...ntial_engine(3) — bye bestie, go seed something iconic 💖✨🎀