replace ComputeMinWork with CheckMinWork

src/main.cpp

@@ -2410,12 +2410,7 @@ bool AcceptBlockHeader(CBlockHeader& block, CValidationState& state, CBlockIndex
             return state.DoS(100, error("CheckBlockHeader() : block with timestamp before last checkpoint"),
                              REJECT_CHECKPOINT, "time-too-old");
         }
-        bool fOverflow = false;
+        if (!CheckMinWork(block.nBits, pcheckpoint->nBits, deltaTime))
-        uint256 bnNewBlock;
-        bnNewBlock.SetCompact(block.nBits, NULL, &fOverflow);
-        uint256 bnRequired;
-        bnRequired.SetCompact(ComputeMinWork(pcheckpoint->nBits, deltaTime));
-        if (fOverflow || bnNewBlock > bnRequired)
         {
             return state.DoS(100, error("CheckBlockHeader() : block with too little proof-of-work"),
                              REJECT_INVALID, "bad-diffbits");

src/pow.cpp

@@ -94,29 +94,36 @@ bool CheckProofOfWork(uint256 hash, unsigned int nBits)
 }
 
 //
-// minimum amount of work that could possibly be required nTime after
+// true if nBits is greater than the minimum amount of work that could
-// minimum work required was nBase
+// possibly be required deltaTime after minimum work required was nBase
 //
-unsigned int ComputeMinWork(unsigned int nBase, int64_t nTime)
+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() && nTime > Params().TargetSpacing()*2)
+    if (Params().AllowMinDifficultyBlocks() && deltaTime > Params().TargetSpacing()*2)
-        return bnLimit.GetCompact();
+        return bnNewBlock <= bnLimit;
 
     uint256 bnResult;
     bnResult.SetCompact(nBase);
-    while (nTime > 0 && bnResult < bnLimit)
+    while (deltaTime > 0 && bnResult < bnLimit)
     {
         // Maximum 400% adjustment...
         bnResult *= 4;
         // ... in best-case exactly 4-times-normal target time
-        nTime -= Params().TargetTimespan()*4;
+        deltaTime -= Params().TargetTimespan()*4;
     }
     if (bnResult > bnLimit)
         bnResult = bnLimit;
-    return bnResult.GetCompact();
+
+    return bnNewBlock <= bnResult;
 }
 
 void UpdateTime(CBlockHeader* pblock, const CBlockIndex* pindexPrev)

src/pow.h

@@ -17,8 +17,8 @@ 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);
-/** Calculate the minimum amount of work a received block needs, without knowing its direct parent */
+/** Check the work is more than the minimum a received block needs, without knowing its direct parent */
-unsigned int ComputeMinWork(unsigned int nBase, int64_t nTime);
+bool CheckMinWork(unsigned int nBits, unsigned int nBase, int64_t deltaTime);
 
 void UpdateTime(CBlockHeader* block, const CBlockIndex* pindexPrev);
 

src/test/DoS_tests.cpp

@@ -106,11 +106,7 @@ static bool CheckNBits(unsigned int nbits1, int64_t time1, unsigned int nbits2,
         return CheckNBits(nbits2, time2, nbits1, time1);
     int64_t deltaTime = time2-time1;
 
-    uint256 required;
+    return CheckMinWork(nbits2, nbits1, deltaTime);
-    required.SetCompact(ComputeMinWork(nbits1, deltaTime));
-    uint256 have;
-    have.SetCompact(nbits2);
-    return (have <= required);
 }
 
 BOOST_AUTO_TEST_CASE(DoS_checknbits)