Remove CheckMinWork, as we always know all parent headers

src/main.cpp

@@ -2329,23 +2329,6 @@ bool AcceptBlockHeader(const CBlockHeader& block, CValidationState& state, CBloc
         return true;
     }
 
-    CBlockIndex* pcheckpoint = Checkpoints::GetLastCheckpoint();
-    if (pcheckpoint && block.hashPrevBlock != (chainActive.Tip() ? chainActive.Tip()->GetBlockHash() : uint256(0)))
-    {
-        // Extra checks to prevent "fill up memory by spamming with bogus blocks"
-        int64_t deltaTime = block.GetBlockTime() - pcheckpoint->GetBlockTime();
-        if (deltaTime < 0)
-        {
-            return state.DoS(100, error("%s : block with timestamp before last checkpoint", __func__),
-                             REJECT_CHECKPOINT, "time-too-old");
-        }
-        if (!CheckMinWork(block.nBits, pcheckpoint->nBits, deltaTime))
-        {
-            return state.DoS(100, error("%s : block with too little proof-of-work", __func__),
-                             REJECT_INVALID, "bad-diffbits");
-        }
-    }
-
     // Get prev block index
     CBlockIndex* pindexPrev = NULL;
     int nHeight = 0;

src/pow.cpp

@@ -98,39 +98,6 @@ bool CheckProofOfWork(uint256 hash, unsigned int nBits)
     return true;
 }
 
-//
-// true if nBits is greater than the minimum amount of work that could
-// possibly be required deltaTime after minimum work required was nBase
-//
-bool CheckMinWork(unsigned int nBits, unsigned int nBase, int64_t deltaTime)
-{
-    bool fOverflow = false;
-    uint256 bnNewBlock;
-    bnNewBlock.SetCompact(nBits, NULL, &fOverflow);
-    if (fOverflow)
-        return false;
-
-    const uint256 &bnLimit = Params().ProofOfWorkLimit();
-    // Testnet has min-difficulty blocks
-    // after Params().TargetSpacing()*2 time between blocks:
-    if (Params().AllowMinDifficultyBlocks() && deltaTime > Params().TargetSpacing()*2)
-        return bnNewBlock <= bnLimit;
-
-    uint256 bnResult;
-    bnResult.SetCompact(nBase);
-    while (deltaTime > 0 && bnResult < bnLimit)
-    {
-        // Maximum 400% adjustment...
-        bnResult *= 4;
-        // ... in best-case exactly 4-times-normal target time
-        deltaTime -= Params().TargetTimespan()*4;
-    }
-    if (bnResult > bnLimit)
-        bnResult = bnLimit;
-
-    return bnNewBlock <= bnResult;
-}
-
 void UpdateTime(CBlockHeader* pblock, const CBlockIndex* pindexPrev)
 {
     pblock->nTime = std::max(pindexPrev->GetMedianTimePast()+1, GetAdjustedTime());

src/pow.h

@@ -16,8 +16,6 @@ unsigned int GetNextWorkRequired(const CBlockIndex* pindexLast, const CBlockHead
 
 /** Check whether a block hash satisfies the proof-of-work requirement specified by nBits */
 bool CheckProofOfWork(uint256 hash, unsigned int nBits);
-/** Check the work is more than the minimum a received block needs, without knowing its direct parent */
-bool CheckMinWork(unsigned int nBits, unsigned int nBase, int64_t deltaTime);
 
 void UpdateTime(CBlockHeader* block, const CBlockIndex* pindexPrev);
 

src/test/DoS_tests.cpp

@@ -106,51 +106,6 @@ BOOST_AUTO_TEST_CASE(DoS_bantime)
     BOOST_CHECK(!CNode::IsBanned(addr));
 }
 
-static bool CheckNBits(unsigned int nbits1, int64_t time1, unsigned int nbits2, int64_t time2)\
-{
-    if (time1 > time2)
-        return CheckNBits(nbits2, time2, nbits1, time1);
-    int64_t deltaTime = time2-time1;
-
-    return CheckMinWork(nbits2, nbits1, deltaTime);
-}
-
-BOOST_AUTO_TEST_CASE(DoS_checknbits)
-{
-    using namespace boost::assign; // for 'map_list_of()'
-
-    // Timestamps,nBits from the bitcoin block chain.
-    // These are the block-chain checkpoint blocks
-    typedef std::map<int64_t, unsigned int> BlockData;
-    BlockData chainData =
-        map_list_of(1239852051,486604799)(1262749024,486594666)
-        (1279305360,469854461)(1280200847,469830746)(1281678674,469809688)
-        (1296207707,453179945)(1302624061,453036989)(1309640330,437004818)
-        (1313172719,436789733);
-
-    // Make sure CheckNBits considers every combination of block-chain-lock-in-points
-    // "sane":
-    BOOST_FOREACH(const BlockData::value_type& i, chainData)
-    {
-        BOOST_FOREACH(const BlockData::value_type& j, chainData)
-        {
-            BOOST_CHECK(CheckNBits(i.second, i.first, j.second, j.first));
-        }
-    }
-
-    // Test a couple of insane combinations:
-    BlockData::value_type firstcheck = *(chainData.begin());
-    BlockData::value_type lastcheck = *(chainData.rbegin());
-
-    // First checkpoint difficulty at or a while after the last checkpoint time should fail when
-    // compared to last checkpoint
-    BOOST_CHECK(!CheckNBits(firstcheck.second, lastcheck.first+60*10, lastcheck.second, lastcheck.first));
-    BOOST_CHECK(!CheckNBits(firstcheck.second, lastcheck.first+60*60*24*14, lastcheck.second, lastcheck.first));
-
-    // ... but OK if enough time passed for difficulty to adjust downward:
-    BOOST_CHECK(CheckNBits(firstcheck.second, lastcheck.first+60*60*24*365*4, lastcheck.second, lastcheck.first));
-}
-
 CTransaction RandomOrphan()
 {
     std::map<uint256, COrphanTx>::iterator it;