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 <uint256.h>

#include <chrono> // For std::chrono::microseconds
#include <cstdint>
#include <limits>

void GetRandBytes(uint8_t *buf, int num) noexcept;
uint64_t GetRand(uint64_t nMax) noexcept;
std::chrono::microseconds
GetRandMicros(std::chrono::microseconds duration_max) noexcept;
int GetRandInt(int nMax) noexcept;
uint256 GetRandHash() noexcept;

void GetStrongRandBytes(uint8_t *buf, int num) noexcept;

void RandAddPeriodic() noexcept;

void RandAddEvent(const uint32_t event_info) noexcept;

class FastRandomContext {
private:
    bool requires_seed;
    ChaCha20 rng;

    uint8_t bytebuf[64];
    int bytebuf_size;

    uint64_t bitbuf;
    int bitbuf_size;

    void RandomSeed();

    void FillByteBuffer() {
        if (requires_seed) {
            RandomSeed();
        }
        rng.Keystream(bytebuf, sizeof(bytebuf));
        bytebuf_size = sizeof(bytebuf);
    }

    void FillBitBuffer() {
        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 (bytebuf_size < 8) {
            FillByteBuffer();
        }
        uint64_t ret = ReadLE64(bytebuf + 64 - bytebuf_size);
        bytebuf_size -= 8;
        return ret;
    }

    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;
            }
        }
    }

    std::vector<uint8_t> randbytes(size_t len);

    uint32_t rand32() noexcept { return randbits(32); }

    uint160 rand160() noexcept;

    uint256 rand256() noexcept;

    bool randbool() noexcept { return randbits(1); }

    // Compatibility with the C++11 UniformRandomBitGenerator concept
    typedef uint64_t result_type;
    static constexpr uint64_t min() { return 0; }
    static constexpr uint64_t max() {
        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