Refactor some pow functions (#3198)

* Refactor GetNextWorkRequired

* Move special diff rule out of DGW

Author: UdjinM6

src/pow.cpp

@@ -79,7 +79,7 @@ unsigned int static KimotoGravityWell(const CBlockIndex* pindexLast, const Conse
     return bnNew.GetCompact();
 }
 
-unsigned int static DarkGravityWave(const CBlockIndex* pindexLast, const CBlockHeader *pblock, const Consensus::Params& params) {
+unsigned int static DarkGravityWave(const CBlockIndex* pindexLast, const Consensus::Params& params) {
     /* current difficulty formula, dash - DarkGravity v3, written by Evan Duffield - evan@dash.org */
     const arith_uint256 bnPowLimit = UintToArith256(params.powLimit);
     int64_t nPastBlocks = 24;
@@ -89,21 +89,6 @@ unsigned int static DarkGravityWave(const CBlockIndex* pindexLast, const CBlockH
         return bnPowLimit.GetCompact();
     }
 
-    if (params.fPowAllowMinDifficultyBlocks) {
-        // recent block is more than 2 hours old
-        if (pblock->GetBlockTime() > pindexLast->GetBlockTime() + 2 * 60 * 60) {
-            return bnPowLimit.GetCompact();
-        }
-        // recent block is more than 10 minutes old
-        if (pblock->GetBlockTime() > pindexLast->GetBlockTime() + params.nPowTargetSpacing * 4) {
-            arith_uint256 bnNew = arith_uint256().SetCompact(pindexLast->nBits) * 10;
-            if (bnNew > bnPowLimit) {
-                bnNew = bnPowLimit;
-            }
-            return bnNew.GetCompact();
-        }
-    }
-
     const CBlockIndex *pindex = pindexLast;
     arith_uint256 bnPastTargetAvg;
 
@@ -182,22 +167,41 @@ unsigned int GetNextWorkRequiredBTC(const CBlockIndex* pindexLast, const CBlockH
 
 unsigned int GetNextWorkRequired(const CBlockIndex* pindexLast, const CBlockHeader *pblock, const Consensus::Params& params)
 {
+    assert(pindexLast != nullptr);
+    assert(pblock != nullptr);
+    const arith_uint256 bnPowLimit = UintToArith256(params.powLimit);
+
     // this is only active on devnets
     if (pindexLast->nHeight < params.nMinimumDifficultyBlocks) {
-        unsigned int nProofOfWorkLimit = UintToArith256(params.powLimit).GetCompact();
-        return nProofOfWorkLimit;
+        return bnPowLimit.GetCompact();
     }
 
-    // Most recent algo first
-    if (pindexLast->nHeight + 1 >= params.nPowDGWHeight) {
-        return DarkGravityWave(pindexLast, pblock, params);
+    if (pindexLast->nHeight + 1 < params.nPowKGWHeight) {
+        return GetNextWorkRequiredBTC(pindexLast, pblock, params);
     }
-    else if (pindexLast->nHeight + 1 >= params.nPowKGWHeight) {
-        return KimotoGravityWell(pindexLast, params);
+
+    // Note: GetNextWorkRequiredBTC has it's own special difficulty rule,
+    // so we only apply this to post-BTC algos.
+    if (params.fPowAllowMinDifficultyBlocks) {
+        // recent block is more than 2 hours old
+        if (pblock->GetBlockTime() > pindexLast->GetBlockTime() + 2 * 60 * 60) {
+            return bnPowLimit.GetCompact();
+        }
+        // recent block is more than 10 minutes old
+        if (pblock->GetBlockTime() > pindexLast->GetBlockTime() + params.nPowTargetSpacing * 4) {
+            arith_uint256 bnNew = arith_uint256().SetCompact(pindexLast->nBits) * 10;
+            if (bnNew > bnPowLimit) {
+                return bnPowLimit.GetCompact();
+            }
+            return bnNew.GetCompact();
+        }
     }
-    else {
-        return GetNextWorkRequiredBTC(pindexLast, pblock, params);
+
+    if (pindexLast->nHeight + 1 < params.nPowDGWHeight) {
+        return KimotoGravityWell(pindexLast, params);
     }
+
+    return DarkGravityWave(pindexLast, params);
 }
 
 // for DIFF_BTC only!