Disable retargeting for regtest

core/src/main/java/org/bitcoinj/core/NetworkParameters.java

@@ -79,6 +79,7 @@ public abstract class NetworkParameters {
     protected int dumpedPrivateKeyHeader;
     protected int interval;
     protected int targetTimespan;
+    protected boolean noRetargeting;
     protected byte[] alertSigningKey;
     protected int bip32HeaderPub;
     protected int bip32HeaderPriv;
@@ -346,6 +347,15 @@ public int getTargetTimespan() {
         return targetTimespan;
     }
 
+    /**
+     * Whether to skip retargeting. 
+     * If set to false, the node works as usual: recalculates the difficulty using targetTimespan and interval.
+     * If set to true, the difficulty is never recalculated
+     */
+    public boolean getNoRetargeting() {
+        return noRetargeting;
+    }    
+
     /**
      * The version codes that prefix addresses which are acceptable on this network. Although Satoshi intended these to
      * be used for "versioning", in fact they are today used to discriminate what kind of data is contained in the

core/src/main/java/org/bitcoinj/params/AbstractBitcoinNetParams.java

@@ -67,7 +67,7 @@ public void checkDifficultyTransitions(final StoredBlock storedPrev, final Block
         Block prev = storedPrev.getHeader();
 
         // Is this supposed to be a difficulty transition point?
-        if (!isDifficultyTransitionPoint(storedPrev)) {
+        if (!isDifficultyTransitionPoint(storedPrev) || getNoRetargeting()) {
 
             // No ... so check the difficulty didn't actually change.
             if (nextBlock.getDifficultyTarget() != prev.getDifficultyTarget())

core/src/main/java/org/bitcoinj/params/MainNetParams.java

@@ -36,6 +36,7 @@ public MainNetParams() {
         super();
         interval = INTERVAL;
         targetTimespan = TARGET_TIMESPAN;
+        noRetargeting = false;
         maxTarget = Utils.decodeCompactBits(0x1d00ffffL);
         dumpedPrivateKeyHeader = 128;
         addressHeader = 0;

core/src/main/java/org/bitcoinj/params/RegTestParams.java

@@ -31,6 +31,7 @@ public class RegTestParams extends TestNet2Params {
     public RegTestParams() {
         super();
         interval = 10000;
+        noRetargeting = true;        
         maxTarget = MAX_TARGET;
         subsidyDecreaseBlockCount = 150;
         port = 18444;

core/src/main/java/org/bitcoinj/params/TestNet2Params.java

@@ -39,6 +39,7 @@ public TestNet2Params() {
         acceptableAddressCodes = new int[] { addressHeader, p2shHeader };
         interval = INTERVAL;
         targetTimespan = TARGET_TIMESPAN;
+        noRetargeting = false;
         maxTarget = Utils.decodeCompactBits(0x1d0fffffL);
         dumpedPrivateKeyHeader = 239;
         genesisBlock.setTime(1296688602L);

core/src/main/java/org/bitcoinj/params/TestNet3Params.java

@@ -42,6 +42,7 @@ public TestNet3Params() {
         packetMagic = 0x0b110907;
         interval = INTERVAL;
         targetTimespan = TARGET_TIMESPAN;
+        noRetargeting = false;
         maxTarget = Utils.decodeCompactBits(0x1d00ffffL);
         port = 18333;
         addressHeader = 111;

core/src/main/java/org/bitcoinj/params/UnitTestParams.java

@@ -44,6 +44,7 @@ public UnitTestParams() {
         interval = 10;
         dumpedPrivateKeyHeader = 239;
         targetTimespan = 200000000;  // 6 years. Just a very big number.
+        noRetargeting = false;        
         spendableCoinbaseDepth = 5;
         subsidyDecreaseBlockCount = 100;
         dnsSeeds = null;