pow_tests.cpp

// Copyright (c) 2015-present The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.

#include <chain.h>
#include <chainparams.h>
#include <pow.h>
#include <test/util/random.h>
#include <test/util/common.h>
#include <test/util/setup_common.h>
#include <util/chaintype.h>

#include <boost/test/unit_test.hpp>

BOOST_FIXTURE_TEST_SUITE(pow_tests, BasicTestingSetup)

/* Test calculation of next difficulty target with no constraints applying */
BOOST_AUTO_TEST_CASE(get_next_work)
{
    const auto chainParams = CreateChainParams(*m_node.args, ChainType::MAIN);
    int64_t nLastRetargetTime = 1261130161; // Block #30240
    CBlockIndex pindexLast;
    pindexLast.nHeight = 32255;
    pindexLast.nTime = 1262152739;  // Block #32255
    pindexLast.nBits = 0x1d00ffff;

    // Here (and below): expected_nbits is calculated in
    // CalculateNextWorkRequired(); redoing the calculation here would be just
    // reimplementing the same code that is written in pow.cpp. Rather than
    // copy that code, we just hardcode the expected result.
    unsigned int expected_nbits = 0x1d00d86aU;
    BOOST_CHECK_EQUAL(CalculateNextWorkRequired(&pindexLast, nLastRetargetTime, chainParams->GetConsensus()), expected_nbits);
    BOOST_CHECK(PermittedDifficultyTransition(chainParams->GetConsensus(), pindexLast.nHeight+1, pindexLast.nBits, expected_nbits));
}

/* Test the constraint on the upper bound for next work */
BOOST_AUTO_TEST_CASE(get_next_work_pow_limit)
{
    const auto chainParams = CreateChainParams(*m_node.args, ChainType::MAIN);
    int64_t nLastRetargetTime = 1231006505; // Block #0
    CBlockIndex pindexLast;
    pindexLast.nHeight = 2015;
    pindexLast.nTime = 1233061996;  // Block #2015
    pindexLast.nBits = 0x1d00ffff;
    unsigned int expected_nbits = 0x1d00ffffU;
    BOOST_CHECK_EQUAL(CalculateNextWorkRequired(&pindexLast, nLastRetargetTime, chainParams->GetConsensus()), expected_nbits);
    BOOST_CHECK(PermittedDifficultyTransition(chainParams->GetConsensus(), pindexLast.nHeight+1, pindexLast.nBits, expected_nbits));
}

/* Test the constraint on the lower bound for actual time taken */
BOOST_AUTO_TEST_CASE(get_next_work_lower_limit_actual)
{
    const auto chainParams = CreateChainParams(*m_node.args, ChainType::MAIN);
    int64_t nLastRetargetTime = 1279008237; // Block #66528
    CBlockIndex pindexLast;
    pindexLast.nHeight = 68543;
    pindexLast.nTime = 1279297671;  // Block #68543
    pindexLast.nBits = 0x1c05a3f4;
    unsigned int expected_nbits = 0x1c0168fdU;
    BOOST_CHECK_EQUAL(CalculateNextWorkRequired(&pindexLast, nLastRetargetTime, chainParams->GetConsensus()), expected_nbits);
    BOOST_CHECK(PermittedDifficultyTransition(chainParams->GetConsensus(), pindexLast.nHeight+1, pindexLast.nBits, expected_nbits));
    // Test that reducing nbits further would not be a PermittedDifficultyTransition.
    unsigned int invalid_nbits = expected_nbits-1;
    BOOST_CHECK(!PermittedDifficultyTransition(chainParams->GetConsensus(), pindexLast.nHeight+1, pindexLast.nBits, invalid_nbits));
}

/* Test that the largest permitted difficulty increase is not itself rejected
 * when the new target is not exactly representable in compact form. */
BOOST_AUTO_TEST_CASE(get_next_work_lower_limit_rounding)
{
    const auto consensus = CreateChainParams(*m_node.args, ChainType::MAIN)->GetConsensus();
    CBlockIndex pindexLast;
    pindexLast.nHeight = 68543;
    pindexLast.nTime = 1279297671;
    pindexLast.nBits = 0x1c05a3f5; // Mantissa is not a multiple of four
    int64_t nLastRetargetTime = pindexLast.nTime - consensus.nPowTargetTimespan/4;
    unsigned int expected_nbits = 0x1c0168fdU;
    BOOST_CHECK_EQUAL(CalculateNextWorkRequired(&pindexLast, nLastRetargetTime, consensus), expected_nbits);
    BOOST_CHECK(PermittedDifficultyTransition(consensus, pindexLast.nHeight+1, pindexLast.nBits, expected_nbits));
}

/* Test the lower bound for a negative actual time taken, which is possible
 * because timestamps only have to exceed the median of the previous eleven. */
BOOST_AUTO_TEST_CASE(get_next_work_negative_actual)
{
    const auto consensus = CreateChainParams(*m_node.args, ChainType::MAIN)->GetConsensus();
    int64_t nLastRetargetTime = 1279297671; // Later than pindexLast.nTime
    CBlockIndex pindexLast;
    pindexLast.nHeight = 68543;
    pindexLast.nTime = 1279008237;
    pindexLast.nBits = 0x1c05a3f4;
    unsigned int expected_nbits = 0x1c0168fdU;
    BOOST_CHECK_EQUAL(CalculateNextWorkRequired(&pindexLast, nLastRetargetTime, consensus), expected_nbits);
    BOOST_CHECK(PermittedDifficultyTransition(consensus, pindexLast.nHeight+1, pindexLast.nBits, expected_nbits));
}

/* Test the constraint on the upper bound for actual time taken */
BOOST_AUTO_TEST_CASE(get_next_work_upper_limit_actual)
{
    const auto chainParams = CreateChainParams(*m_node.args, ChainType::MAIN);
    int64_t nLastRetargetTime = 1263163443; // NOTE: Not an actual block time
    CBlockIndex pindexLast;
    pindexLast.nHeight = 46367;
    pindexLast.nTime = 1269211443;  // Block #46367
    pindexLast.nBits = 0x1c387f6f;
    unsigned int expected_nbits = 0x1d00e1fdU;
    BOOST_CHECK_EQUAL(CalculateNextWorkRequired(&pindexLast, nLastRetargetTime, chainParams->GetConsensus()), expected_nbits);
    BOOST_CHECK(PermittedDifficultyTransition(chainParams->GetConsensus(), pindexLast.nHeight+1, pindexLast.nBits, expected_nbits));
    // Test that increasing nbits further would not be a PermittedDifficultyTransition.
    unsigned int invalid_nbits = expected_nbits+1;
    BOOST_CHECK(!PermittedDifficultyTransition(chainParams->GetConsensus(), pindexLast.nHeight+1, pindexLast.nBits, invalid_nbits));
}

/* Test that the retarget window starts at the timestamp of the first block
 * of the window, not its median time past. */
BOOST_AUTO_TEST_CASE(get_next_work_first_block_time)
{
    const auto consensus = CreateChainParams(*m_node.args, ChainType::MAIN)->GetConsensus();
    const int64_t interval{consensus.DifficultyAdjustmentInterval()};

    // Two retarget windows, so that the first block of the second one has
    // ancestors and hence a median time past earlier than its own time.
    std::vector<CBlockIndex> blocks(2 * interval);
    for (int64_t i = 0; i < 2 * interval; i++) {
        blocks[i].pprev = i ? &blocks[i - 1] : nullptr;
        blocks[i].nHeight = i;
        blocks[i].nTime = 1269211443 + i * consensus.nPowTargetSpacing;
        blocks[i].nBits = 0x1c05a3f4;
    }

    const CBlockIndex& first{blocks[interval]};
    const CBlockIndex& last{blocks[2 * interval - 1]};
    BOOST_CHECK_NE(first.GetBlockTime(), first.GetMedianTimePast());
    unsigned int expected_nbits = 0x1c05a33c;
    BOOST_CHECK_EQUAL(GetNextWorkRequired(&last, nullptr, consensus), expected_nbits);
    BOOST_CHECK(PermittedDifficultyTransition(consensus, last.nHeight+1, last.nBits, expected_nbits));
}

/* Test that nbits is only permitted to change at a difficulty adjustment. */
BOOST_AUTO_TEST_CASE(permitted_difficulty_transition_no_retarget)
{
    const auto consensus = CreateChainParams(*m_node.args, ChainType::MAIN)->GetConsensus();
    const int64_t height{consensus.DifficultyAdjustmentInterval() + 1}; // Not a retarget height

    const unsigned int nbits{0x1c05a3f4};
    BOOST_CHECK(PermittedDifficultyTransition(consensus, height, nbits, nbits));
    BOOST_CHECK(!PermittedDifficultyTransition(consensus, height, nbits, nbits - 1));
    BOOST_CHECK(!PermittedDifficultyTransition(consensus, height, nbits, nbits + 1));
}

BOOST_AUTO_TEST_CASE(CheckProofOfWork_test_negative_target)
{
    const auto consensus = CreateChainParams(*m_node.args, ChainType::MAIN)->GetConsensus();
    uint256 hash;
    unsigned int nBits;
    nBits = UintToArith256(consensus.powLimit).GetCompact(true);
    hash = uint256{1};
    BOOST_CHECK(!CheckProofOfWork(hash, nBits, consensus));
}

BOOST_AUTO_TEST_CASE(CheckProofOfWork_test_overflow_target)
{
    const auto consensus = CreateChainParams(*m_node.args, ChainType::MAIN)->GetConsensus();
    uint256 hash;
    unsigned int nBits{~0x00800000U};
    hash = uint256{1};
    BOOST_CHECK(!CheckProofOfWork(hash, nBits, consensus));
}

BOOST_AUTO_TEST_CASE(CheckProofOfWork_test_too_easy_target)
{
    const auto consensus = CreateChainParams(*m_node.args, ChainType::MAIN)->GetConsensus();
    uint256 hash;
    unsigned int nBits;
    arith_uint256 nBits_arith = UintToArith256(consensus.powLimit);
    nBits_arith *= 2;
    nBits = nBits_arith.GetCompact();
    hash = uint256{1};
    BOOST_CHECK(!CheckProofOfWork(hash, nBits, consensus));
}

BOOST_AUTO_TEST_CASE(CheckProofOfWork_test_biger_hash_than_target)
{
    const auto consensus = CreateChainParams(*m_node.args, ChainType::MAIN)->GetConsensus();
    uint256 hash;
    unsigned int nBits;
    arith_uint256 hash_arith = UintToArith256(consensus.powLimit);
    nBits = hash_arith.GetCompact();
    hash_arith *= 2; // hash > nBits
    hash = ArithToUint256(hash_arith);
    BOOST_CHECK(!CheckProofOfWork(hash, nBits, consensus));
}

BOOST_AUTO_TEST_CASE(CheckProofOfWork_test_zero_target)
{
    const auto consensus = CreateChainParams(*m_node.args, ChainType::MAIN)->GetConsensus();
    uint256 hash;
    unsigned int nBits;
    arith_uint256 hash_arith{0};
    nBits = hash_arith.GetCompact();
    hash = ArithToUint256(hash_arith);
    BOOST_CHECK(!CheckProofOfWork(hash, nBits, consensus));
}

BOOST_AUTO_TEST_CASE(GetBitsProof_test)
{
    // Targets that are zero, negative or overflow encode no work.
    BOOST_CHECK_EQUAL(GetBitsProof(0x00000000), arith_uint256{0});
    BOOST_CHECK_EQUAL(GetBitsProof(0x01003456), arith_uint256{0});
    BOOST_CHECK_EQUAL(GetBitsProof(0x04923456), arith_uint256{0});
    BOOST_CHECK_EQUAL(GetBitsProof(0xff123456), arith_uint256{0});
    // The exponent byte is unsigned, so this is a large exponent that overflows.
    BOOST_CHECK_EQUAL(GetBitsProof(0x80010203), arith_uint256{0});
    // The two overflows above shift every mantissa bit out of 256 bits, so they would
    // also give zero work without the overflow check. This one keeps the low bits of
    // its mantissa when truncated.
    BOOST_CHECK_EQUAL(GetBitsProof(0x21012345), arith_uint256{0});
    // The genesis block target.
    BOOST_CHECK_EQUAL(GetBitsProof(0x1d00ffff), arith_uint256{0x100010001});
}

BOOST_AUTO_TEST_CASE(GetBlockProofEquivalentTime_test)
{
    const auto chainParams = CreateChainParams(*m_node.args, ChainType::MAIN);
    std::vector<CBlockIndex> blocks(10000);
    for (int i = 0; i < 10000; i++) {
        blocks[i].pprev = i ? &blocks[i - 1] : nullptr;
        blocks[i].nHeight = i;
        blocks[i].nTime = 1269211443 + i * chainParams->GetConsensus().nPowTargetSpacing;
        blocks[i].nBits = 0x207fffff; /* target 0x7fffff000... */
        blocks[i].nChainWork = i ? blocks[i - 1].nChainWork + GetBlockProof(blocks[i - 1]) : arith_uint256(0);
    }

    for (int j = 0; j < 1000; j++) {
        CBlockIndex *p1 = &blocks[m_rng.randrange(10000)];
        CBlockIndex *p2 = &blocks[m_rng.randrange(10000)];
        CBlockIndex *p3 = &blocks[m_rng.randrange(10000)];

        int64_t tdiff = GetBlockProofEquivalentTime(*p1, *p2, *p3, chainParams->GetConsensus());
        BOOST_CHECK_EQUAL(tdiff, p1->GetBlockTime() - p2->GetBlockTime());
    }
}

void sanity_check_chainparams(const ArgsManager& args, ChainType chain_type)
{
    const auto chainParams = CreateChainParams(args, chain_type);
    const auto consensus = chainParams->GetConsensus();

    // hash genesis is correct
    BOOST_CHECK_EQUAL(consensus.hashGenesisBlock, chainParams->GenesisBlock().GetHash());

    // target timespan is an even multiple of spacing
    BOOST_CHECK_EQUAL(consensus.nPowTargetTimespan % consensus.nPowTargetSpacing, 0);

    // genesis nBits is positive, doesn't overflow and is lower than powLimit
    arith_uint256 pow_compact;
    bool neg, over;
    pow_compact.SetCompact(chainParams->GenesisBlock().nBits, &neg, &over);
    BOOST_CHECK(!neg);
    BOOST_CHECK(pow_compact != 0);
    BOOST_CHECK(!over);
    BOOST_CHECK(UintToArith256(consensus.powLimit) >= pow_compact);

    // check max target * 4*nPowTargetTimespan doesn't overflow -- see pow.cpp:CalculateNextWorkRequired()
    if (!consensus.fPowNoRetargeting) {
        arith_uint256 targ_max{UintToArith256(uint256{"ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff"})};
        targ_max /= consensus.nPowTargetTimespan*4;
        BOOST_CHECK(UintToArith256(consensus.powLimit) < targ_max);
    }
}

BOOST_AUTO_TEST_CASE(ChainParams_MAIN_sanity)
{
    sanity_check_chainparams(*m_node.args, ChainType::MAIN);
}

BOOST_AUTO_TEST_CASE(ChainParams_REGTEST_sanity)
{
    sanity_check_chainparams(*m_node.args, ChainType::REGTEST);
}

BOOST_AUTO_TEST_CASE(ChainParams_TESTNET_sanity)
{
    sanity_check_chainparams(*m_node.args, ChainType::TESTNET);
}

BOOST_AUTO_TEST_CASE(ChainParams_TESTNET4_sanity)
{
    sanity_check_chainparams(*m_node.args, ChainType::TESTNET4);
}

BOOST_AUTO_TEST_CASE(ChainParams_SIGNET_sanity)
{
    sanity_check_chainparams(*m_node.args, ChainType::SIGNET);
}

BOOST_AUTO_TEST_SUITE_END()