random.h

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// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-2016 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
#ifndef BITCOIN_RANDOM_H
#define BITCOIN_RANDOM_H
 
#include <crypto/chacha20.h>
#include <crypto/common.h>
#include <span.h>
#include <uint256.h>
 
#include <chrono>
#include <cstdint>
#include <limits>
 
void GetRandBytes(Span<uint8_t> bytes) noexcept;
uint64_t GetRandInternal(uint64_t nMax) noexcept;
template <typename T>
T GetRand(T nMax = std::numeric_limits<T>::max()) noexcept {
    static_assert(std::is_integral<T>(), "T must be integral");
    static_assert(std::numeric_limits<T>::max() <=
                      std::numeric_limits<uint64_t>::max(),
                  "GetRand only supports up to uint64_t");
    return T(GetRandInternal(nMax));
}
template <typename D>
D GetRandomDuration(typename std::common_type<D>::type max) noexcept {
    // Having the compiler infer the template argument from the function
    // argument is dangerous, because the desired return value generally has a
    // different type than the function argument. So std::common_type is used to
    // force the call site to specify the type of the return value.
 
    assert(max.count() > 0);
    return D{GetRand(max.count())};
};
constexpr auto GetRandMicros = GetRandomDuration<std::chrono::microseconds>;
constexpr auto GetRandMillis = GetRandomDuration<std::chrono::milliseconds>;
 
std::chrono::microseconds
GetExponentialRand(std::chrono::microseconds now,
                   std::chrono::seconds average_interval);
 
uint256 GetRandHash() noexcept;
 
void GetStrongRandBytes(Span<uint8_t> bytes) noexcept;
 
void RandAddPeriodic() noexcept;
 
void RandAddEvent(const uint32_t event_info) noexcept;
 
class FastRandomContext {
private:
    bool requires_seed;
    ChaCha20 rng;
 
    uint64_t bitbuf;
    int bitbuf_size;
 
    void RandomSeed() noexcept;
 
    void FillBitBuffer() noexcept {
        bitbuf = rand64();
        bitbuf_size = 64;
    }
 
public:
    explicit FastRandomContext(bool fDeterministic = false) noexcept;
 
    explicit FastRandomContext(const uint256 &seed) noexcept;
 
    // Do not permit copying a FastRandomContext (move it, or create a new one
    // to get reseeded).
    FastRandomContext(const FastRandomContext &) = delete;
    FastRandomContext(FastRandomContext &&) = delete;
    FastRandomContext &operator=(const FastRandomContext &) = delete;
 
    FastRandomContext &operator=(FastRandomContext &&from) noexcept;
 
    uint64_t rand64() noexcept {
        if (requires_seed) {
            RandomSeed();
        }
        std::array<std::byte, 8> buf;
        rng.Keystream(buf);
        return ReadLE64(UCharCast(buf.data()));
    }
 
    uint64_t randbits(int bits) noexcept {
        if (bits == 0) {
            return 0;
        } else if (bits > 32) {
            return rand64() >> (64 - bits);
        } else {
            if (bitbuf_size < bits) {
                FillBitBuffer();
            }
            uint64_t ret = bitbuf & (~uint64_t(0) >> (64 - bits));
            bitbuf >>= bits;
            bitbuf_size -= bits;
            return ret;
        }
    }
 
    uint64_t randrange(uint64_t range) noexcept {
        assert(range);
        --range;
        int bits = CountBits(range);
        while (true) {
            uint64_t ret = randbits(bits);
            if (ret <= range) {
                return ret;
            }
        }
    }
 
    template <BasicByte B = uint8_t>
    std::vector<B> randbytes(size_t len) noexcept {
        std::vector<B> ret(len);
        fillrand(MakeWritableByteSpan(ret));
        return ret;
    }
 
    void fillrand(Span<std::byte> output) noexcept;
 
    uint32_t rand32() noexcept { return randbits(32); }
 
    uint160 rand160() noexcept {
        uint160 ret;
        fillrand(MakeWritableByteSpan(ret));
        return ret;
    }
 
    uint256 rand256() noexcept {
        uint256 ret;
        fillrand(MakeWritableByteSpan(ret));
        return ret;
    }
 
    bool randbool() noexcept { return randbits(1); }
 
    template <typename Tp>
    Tp rand_uniform_delay(const Tp &time,
                          typename Tp::duration range) noexcept {
        using Dur = typename Tp::duration;
        Dur dur{range.count() > 0
                    ? /* interval [0..range) */ Dur{randrange(range.count())}
                : range.count() < 0
                    ? /* interval (range..0] */ -Dur{randrange(-range.count())}
                    :
                    /* interval [0..0] */ Dur{0}};
        return time + dur;
    }
 
    // Compatibility with the C++11 UniformRandomBitGenerator concept
    typedef uint64_t result_type;
    static constexpr uint64_t min() noexcept { return 0; }
    static constexpr uint64_t max() noexcept {
        return std::numeric_limits<uint64_t>::max();
    }
    inline uint64_t operator()() noexcept { return rand64(); }
};
 
template <typename I, typename R> void Shuffle(I first, I last, R &&rng) {
    while (first != last) {
        size_t j = rng.randrange(last - first);
        if (j) {
            using std::swap;
            swap(*first, *(first + j));
        }
        ++first;
    }
}
 
static const int NUM_OS_RANDOM_BYTES = 32;
 
void GetOSRand(uint8_t *ent32);
 
bool Random_SanityCheck();
 
void RandomInit();
 
#endif // BITCOIN_RANDOM_H