std::generate_canonical(3)

💖 std::generate_canonical 💖

From the C++ Standard Libary manual, bestie — yes, that’s the exact spelling on the page, don’t come for me 💅. This is the C++ random-number glow-up moment.

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✨ NAME ✨

std::generate_canonical — std::generate_canonical. That’s the name, that’s the function, that’s the whole vibe. 👑

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🌀 Synopsis 🌀

Defined in header <random>:

template< class RealType, std::size_t Bits, class Generator >  (since C++11)
RealType generate_canonical( Generator& g );

Generates a random floating point number in range [0, 1).

To generate enough entropy, generate_canonical() will call g() exactly k times, where k = max(1, ⌈ b / log_2 R ⌉) — the page also writes it as k = \max(1, \lceil \frac{b}{\log_2 R} \rceil) — and:

• b = std::min(Bits, std::size_t{std::numeric_limits<RealType>::digits}),
• R = g.max() - g.min() + 1.

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🎀 Parameters 🎀

• g — generator to use to acquire entropy.

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🌸 Return value 🌸

Floating point value in range [0, 1).

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🦋 Exceptions 🦋

None except from those thrown by g.

fr fr, the only drama comes from g. No extra surprises from this function itself. 🫶

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💅 Notes 💅

Some existing implementations have a bug where they may occasionally return 1.0 if RealType is float: GCC #63176, LLVM #18767, MSVC STL #1074. This is LWG issue 2524.

Not me warning you about a bug that can hand you 1.0 when the range says [0, 1) 😭 — that’s the whole point of the note. Keep it in mind.

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🍓 Example 🍓

Produce random numbers with 10 bits of randomness: this may produce only k * R distinct values.

Run this code:

#include <iostream>
#include <random>

int main()
{
    std::random_device rd;
    std::mt19937 gen(rd());
    for (int n = 0; n < 10; ++n)
        std::cout << std::generate_canonical<double, 10>(gen) << ' ';
    std::cout << '\n';
}

⭐ Possible output ⭐

0.208143 0.824147 0.0278604 0.343183 0.0173263 0.864057 0.647037 0.539467 0.0583497 0.609219

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🌈 See also 🌈

• uniform_real_distribution produces real values evenly distributed across a range (C++11) (class template).

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okay bestie that’s the whole page 💜 — source: http://cppreference.com, version/date: 2024.06.10. Go generate something canonical, ily! 🌟🎀