diff --git a/src/com/google/bitcoin/core/Block.java b/src/com/google/bitcoin/core/Block.java
index a2b75db4..f0e91a6a 100644
--- a/src/com/google/bitcoin/core/Block.java
+++ b/src/com/google/bitcoin/core/Block.java
@@ -27,10 +27,10 @@ import static com.google.bitcoin.core.Utils.*;
/**
* A block is the foundation of the BitCoin system. It records a set of {@link Transaction}s together with
* some data that links it into a place in the global block chain, and proves that a difficult calculation was done
- * over its contents. See the BitCoin technical paper for more detail on blocks.
+ * over its contents. See the BitCoin technical paper for more detail on blocks.
*
- * To get a block, you can either build one from the raw bytes you can get from another implementation, or more likely
- * you grab it from a downloaded {@link BlockChain}.
+ * To get a block, you can either build one from the raw bytes you can get from another implementation,
+ * or request one specifically using {@link Peer#getBlock(byte[])}, or grab one from a downloaded {@link BlockChain}.
*/
public class Block extends Message {
private static final long serialVersionUID = 2738848929966035281L;
@@ -142,6 +142,21 @@ public class Block extends Message {
return hash;
}
+ /** The number that is one greater than the largest representable SHA-256 hash. */
+ static private BigInteger LARGEST_HASH = BigInteger.ONE.shiftLeft(256);
+
+ /**
+ * Returns the work represented by this block.
+ *
+ * Work is defined as the number of tries needed to solve a block in the average case. Consider a difficulty
+ * target that covers 5% of all possible hash values. Then the work of the block will be 20. As the target gets
+ * lower, the amount of work goes up.
+ */
+ public BigInteger getWork() throws VerificationException {
+ BigInteger target = getDifficultyTargetAsInteger();
+ return LARGEST_HASH.divide(target.add(BigInteger.ONE));
+ }
+
/**
* Returns a multi-line string containing a description of the contents of the block. Use for debugging purposes
* only.
@@ -183,6 +198,18 @@ public class Block extends Message {
}
}
+ /**
+ * Returns the difficulty target as a 256 bit value that can be compared to a SHA-256 hash. Inside a block the
+ * target is represented using a compact form. If this form decodes to a value that is out of bounds,
+ * an exception is thrown.
+ */
+ public BigInteger getDifficultyTargetAsInteger() throws VerificationException {
+ BigInteger target = Utils.decodeCompactBits(difficultyTarget);
+ if (target.compareTo(BigInteger.valueOf(0)) <= 0 || target.compareTo(params.proofOfWorkLimit) > 0)
+ throw new VerificationException("Difficulty target is bad");
+ return target;
+ }
+
/** Returns true if the hash of the block is OK (lower than difficulty target). */
private boolean checkProofOfWork(boolean throwException) throws VerificationException {
// This part is key - it is what proves the block was as difficult to make as it claims
@@ -193,10 +220,7 @@ public class Block extends Message {
//
// To prevent this attack from being possible, elsewhere we check that the difficultyTarget
// field is of the right value. This requires us to have the preceeding blocks.
- BigInteger target = Utils.decodeCompactBits(difficultyTarget);
-
- if (target.compareTo(BigInteger.valueOf(0)) <= 0 || target.compareTo(params.proofOfWorkLimit) > 0)
- throw new VerificationException("Difficulty target is bad");
+ BigInteger target = getDifficultyTargetAsInteger();
BigInteger h = new BigInteger(1, getHash());
if (h.compareTo(target) > 0) {
@@ -392,13 +416,6 @@ public class Block extends Message {
return difficultyTarget;
}
- /**
- * Returns the difficulty target as a 256 bit value that can be compared to a SHA-256 hash.
- */
- public BigInteger getDifficultyTargetBI() {
- return Utils.decodeCompactBits(getDifficultyTarget());
- }
-
public void setDifficultyTarget(long compactForm) {
this.difficultyTarget = compactForm;
this.hash = null;
diff --git a/src/com/google/bitcoin/core/BlockChain.java b/src/com/google/bitcoin/core/BlockChain.java
index d8963528..687045d2 100644
--- a/src/com/google/bitcoin/core/BlockChain.java
+++ b/src/com/google/bitcoin/core/BlockChain.java
@@ -22,7 +22,6 @@ import java.util.Arrays;
import java.util.LinkedList;
import static com.google.bitcoin.core.Utils.LOG;
-import static com.google.bitcoin.core.Utils.bytesToHexString;
/**
* A BlockChain holds a series of {@link Block} objects, links them together, and knows how to verify that the
@@ -50,10 +49,7 @@ import static com.google.bitcoin.core.Utils.bytesToHexString;
*/
public class BlockChain {
// This is going away.
- private final LinkedList blockChain = new LinkedList();
-
- /** Each chain head that we saw so far. */
- private final ArrayList chainHeads = new ArrayList();
+ private final LinkedList blockChain;
private final NetworkParameters params;
private final Wallet wallet;
@@ -63,6 +59,7 @@ public class BlockChain {
private final ArrayList unconnectedBlocks = new ArrayList();
public BlockChain(NetworkParameters params, Wallet wallet) {
+ blockChain = new LinkedList();
blockChain.add(params.genesisBlock);
this.params = params;
this.wallet = wallet;
@@ -119,7 +116,7 @@ public class BlockChain {
unconnectedBlocks.add(block);
return false;
}
- checkDifficultyTransitions(block);
+ checkDifficultyTransitions(prev, block);
// The block is OK so let's build the rest of the chain on it.
block.prevBlock = prev;
blockChain.add(block);
@@ -158,14 +155,13 @@ public class BlockChain {
static private final int TARGET_SPACING = 10 * 60;
static private final int INTERVAL = TARGET_TIMESPAN / TARGET_SPACING;
- private void checkDifficultyTransitions(Block top) throws VerificationException {
- Block prev = blockChain.getLast();
+ private void checkDifficultyTransitions(Block prev, Block next) throws VerificationException {
// Is this supposed to be a difficulty transition point?
if (blockChain.size() % INTERVAL != 0) {
// No ... so check the difficulty didn't actually change.
- if (top.getDifficultyTarget() != prev.getDifficultyTarget())
+ if (next.getDifficultyTarget() != prev.getDifficultyTarget())
throw new VerificationException("Unexpected change in difficulty at height " + blockChain.size() +
- ": " + Long.toHexString(top.getDifficultyTarget()) + " vs " +
+ ": " + Long.toHexString(next.getDifficultyTarget()) + " vs " +
Long.toHexString(prev.getDifficultyTarget()));
return;
}
@@ -186,8 +182,8 @@ public class BlockChain {
newDifficulty = params.proofOfWorkLimit;
}
- int accuracyBytes = (int) (top.getDifficultyTarget() >>> 24) - 3;
- BigInteger receivedDifficulty = top.getDifficultyTargetBI();
+ int accuracyBytes = (int) (next.getDifficultyTarget() >>> 24) - 3;
+ BigInteger receivedDifficulty = next.getDifficultyTargetAsInteger();
// The calculated difficulty is to a higher precision than received, so reduce here.
BigInteger mask = BigInteger.valueOf(0xFFFFFFL).shiftLeft(accuracyBytes * 8);
diff --git a/tests/com/google/bitcoin/core/BlockTest.java b/tests/com/google/bitcoin/core/BlockTest.java
index cea00544..f9aecb9f 100644
--- a/tests/com/google/bitcoin/core/BlockTest.java
+++ b/tests/com/google/bitcoin/core/BlockTest.java
@@ -23,6 +23,7 @@ import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
+import java.math.BigInteger;
import java.util.Arrays;
import static org.junit.Assert.*;
@@ -37,6 +38,15 @@ public class BlockTest {
blockBytes = Hex.decode("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}
+ @Test
+ public void testWork() throws Exception {
+ BigInteger work = params.genesisBlock.getWork();
+ // This number is printed by the official client at startup as the calculated value of chainWork on testnet:
+ //
+ // SetBestChain: new best=00000007199508e34a9f height=0 work=536879104
+ assertEquals(BigInteger.valueOf(536879104L), work);
+ }
+
@Test
public void testBlockVerification() throws Exception {
Block block = new Block(params, blockBytes);