text: // Copyright (c) 2015 The Bitcoin Core developers
  // Distributed under the MIT/X11 software license, see the accompanying
  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  
  #include "main.h"
  #include "pow.h"
  #include "util.h"
  #include "test/test_bitcoin.h"
  
  #include <boost/test/unit_test.hpp>
  
  using namespace std;
  
  BOOST_FIXTURE_TEST_SUITE(pow_tests, BasicTestingSetup)
  
  /* Test calculation of next difficulty target with no constraints applying */
  BOOST_AUTO_TEST_CASE(get_next_work)
  {
      SelectParams(CBaseChainParams::MAIN);
      const Consensus::Params& params = Params().GetConsensus();
  
      int64_t nLastRetargetTime = 1261130161; // Block #30240
      CBlockIndex pindexLast;
      pindexLast.nHeight = 32255;
      pindexLast.nTime = 1262152739;  // Block #32255
      pindexLast.nBits = 0x1d00ffff;
      BOOST_CHECK_EQUAL(CalculateNextWorkRequired(&pindexLast, nLastRetargetTime, params), 0x1d00d86a);
  }
  
  /* Test the constraint on the upper bound for next work */
  BOOST_AUTO_TEST_CASE(get_next_work_pow_limit)
  {
      SelectParams(CBaseChainParams::MAIN);
      const Consensus::Params& params = Params().GetConsensus();
  
      int64_t nLastRetargetTime = 1231006505; // Block #0
      CBlockIndex pindexLast;
      pindexLast.nHeight = 2015;
      pindexLast.nTime = 1233061996;  // Block #2015
      pindexLast.nBits = 0x1d00ffff;
      BOOST_CHECK_EQUAL(CalculateNextWorkRequired(&pindexLast, nLastRetargetTime, params), 0x1d00ffff);
  }
  
  /* Test the constraint on the lower bound for actual time taken */
  BOOST_AUTO_TEST_CASE(get_next_work_lower_limit_actual)
  {
      SelectParams(CBaseChainParams::MAIN);
      const Consensus::Params& params = Params().GetConsensus();
  
      int64_t nLastRetargetTime = 1279008237; // Block #66528
      CBlockIndex pindexLast;
      pindexLast.nHeight = 68543;
      pindexLast.nTime = 1279297671;  // Block #68543
      pindexLast.nBits = 0x1c05a3f4;
      BOOST_CHECK_EQUAL(CalculateNextWorkRequired(&pindexLast, nLastRetargetTime, params), 0x1c0168fd);
  }
  
  /* Test the constraint on the upper bound for actual time taken */
  BOOST_AUTO_TEST_CASE(get_next_work_upper_limit_actual)
  {
      SelectParams(CBaseChainParams::MAIN);
      const Consensus::Params& params = Params().GetConsensus();
  
      int64_t nLastRetargetTime = 1263163443; // NOTE: Not an actual block time
      CBlockIndex pindexLast;
      pindexLast.nHeight = 46367;
      pindexLast.nTime = 1269211443;  // Block #46367
      pindexLast.nBits = 0x1c387f6f;
      BOOST_CHECK_EQUAL(CalculateNextWorkRequired(&pindexLast, nLastRetargetTime, params), 0x1d00e1fd);
  }
  
  BOOST_AUTO_TEST_CASE(GetBlockProofEquivalentTime_test)
  {
      SelectParams(CBaseChainParams::MAIN);
      const Consensus::Params& params = Params().GetConsensus();
  
      std::vector<CBlockIndex> blocks(10000);
      for (int i = 0; i < 10000; i++) {
          blocks[i].pprev = i ? &blocks[i - 1] : NULL;
          blocks[i].nHeight = i;
          blocks[i].nTime = 1269211443 + i * params.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[GetRand(10000)];
          CBlockIndex *p2 = &blocks[GetRand(10000)];
          CBlockIndex *p3 = &blocks[GetRand(10000)];
  
          int64_t tdiff = GetBlockProofEquivalentTime(*p1, *p2, *p3, params);
          BOOST_CHECK_EQUAL(tdiff, p1->GetBlockTime() - p2->GetBlockTime());
      }
  }
  
  static CBlockIndex GetBlockIndex(CBlockIndex *pindexPrev, int64_t nTimeInterval,
                                   uint32_t nBits) {
      CBlockIndex block;
      block.pprev = pindexPrev;
      block.nHeight = pindexPrev->nHeight + 1;
      block.nTime = pindexPrev->nTime + nTimeInterval;
      block.nBits = nBits;
  
      return block;
  }
  
  BOOST_AUTO_TEST_CASE(retargeting_test) {
      mapArgs["-uahftime"] = "1";
      SelectParams(CBaseChainParams::MAIN);
      const Consensus::Params &params = Params().GetConsensus();
  
      std::vector<CBlockIndex> blocks(115);
  
      const arith_uint256 powLimit = UintToArith256(params.powLimit);
      arith_uint256 currentPow = powLimit >> 1;
      uint32_t initialBits = currentPow.GetCompact();
  
      // Genesis block?
      blocks[0] = CBlockIndex();
      blocks[0].nHeight = 0;
      blocks[0].nTime = 1269211443;
      blocks[0].nBits = initialBits;
  
      // Pile up some blocks.
      for (size_t i = 1; i < 100; i++) {
          blocks[i] = GetBlockIndex(&blocks[i - 1], params.nPowTargetSpacing,
                                    initialBits);
      }
  
      CBlockHeader blkHeaderDummy;
  
      // We start getting 2h blocks time. For the first 5 blocks, it doesn't
      // matter as the MTP is not affected. For the next 5 block, MTP difference
      // increases but stays below 12h.
      for (size_t i = 100; i < 110; i++) {
          blocks[i] = GetBlockIndex(&blocks[i - 1], 2 * 3600, initialBits);
          BOOST_CHECK_EQUAL(
              GetNextWorkRequired(&blocks[i], &blkHeaderDummy, params),
              initialBits);
      }
  
      // Now we expect the difficulty to decrease.
      blocks[110] = GetBlockIndex(&blocks[109], 2 * 3600, initialBits);
      currentPow.SetCompact(currentPow.GetCompact());
      currentPow += (currentPow >> 2);
      BOOST_CHECK_EQUAL(
          GetNextWorkRequired(&blocks[110], &blkHeaderDummy, params),
          currentPow.GetCompact());
  
      // As we continue with 2h blocks, difficulty continue to decrease.
      blocks[111] =
          GetBlockIndex(&blocks[110], 2 * 3600, currentPow.GetCompact());
      currentPow.SetCompact(currentPow.GetCompact());
      currentPow += (currentPow >> 2);
      BOOST_CHECK_EQUAL(
          GetNextWorkRequired(&blocks[111], &blkHeaderDummy, params),
          currentPow.GetCompact());
  
      // We decrease again.
      blocks[112] =
          GetBlockIndex(&blocks[111], 2 * 3600, currentPow.GetCompact());
      currentPow.SetCompact(currentPow.GetCompact());
      currentPow += (currentPow >> 2);
      BOOST_CHECK_EQUAL(
          GetNextWorkRequired(&blocks[112], &blkHeaderDummy, params),
          currentPow.GetCompact());
  
      // We check that we do not go below the minimal difficulty.
      blocks[113] =
          GetBlockIndex(&blocks[112], 2 * 3600, currentPow.GetCompact());
      currentPow.SetCompact(currentPow.GetCompact());
      currentPow += (currentPow >> 2);
      BOOST_CHECK(powLimit.GetCompact() != currentPow.GetCompact());
      BOOST_CHECK_EQUAL(
          GetNextWorkRequired(&blocks[113], &blkHeaderDummy, params),
          powLimit.GetCompact());
  
      // Once we reached the minimal difficulty, we stick with it.
      blocks[114] = GetBlockIndex(&blocks[113], 2 * 3600, powLimit.GetCompact());
      BOOST_CHECK(powLimit.GetCompact() != currentPow.GetCompact());
      BOOST_CHECK_EQUAL(
          GetNextWorkRequired(&blocks[114], &blkHeaderDummy, params),
          powLimit.GetCompact());
  
      mapArgs.erase("-uahftime");
  }
  
  BOOST_AUTO_TEST_SUITE_END()
  