Class FastRandomContext

src/random.h:385–414

* Fast randomness source. This is seeded once with secure random data, but * is completely deterministic and does not gather more entropy after that. * * This class is not thread-safe. */

 * This class is not thread-safe.
 */
class FastRandomContext : public RandomMixin<FastRandomContext>
{
private:
    bool requires_seed;
    ChaCha20 rng;

    void RandomSeed() noexcept;

public:
    /** Construct a FastRandomContext with GetRandHash()-based entropy (or zero key if fDeterministic). */
    explicit FastRandomContext(bool fDeterministic = false) noexcept;

    /** Initialize with explicit seed (only for testing) */
    explicit FastRandomContext(const uint256& seed) noexcept;

    /** Reseed with explicit seed (only for testing). */
    void Reseed(const uint256& seed) noexcept;

    /** Generate a random 64-bit integer. */
    uint64_t rand64() noexcept
    {
        if (requires_seed) RandomSeed();
        std::array<std::byte, 8> buf;
        rng.Keystream(buf);
        return ReadLE64(buf.data());
    }

    /** Fill a byte span with random bytes. This overrides the RandomMixin version. */
    void fillrand(std::span<std::byte> output) noexcept;
};

/** xoroshiro128++ PRNG. Extremely fast, not appropriate for cryptographic purposes.
 *