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authorMatt Corallo <git@bluematt.me>2012-08-13 05:26:27 +0200
committerMatt Corallo <git@bluematt.me>2013-01-16 12:48:01 -0500
commitbd21612c37cf4f2df3a6926beff8a7f89714235e (patch)
tree3c192ac4bb78ac67847cfbda463876587a1e61d9 /src/bloom.cpp
parent7ab026f4493b145f2255d816864cb1a3486e0788 (diff)
Add a CBloomFilter class for use as a transaction filter.
Diffstat (limited to 'src/bloom.cpp')
-rw-r--r--src/bloom.cpp133
1 files changed, 133 insertions, 0 deletions
diff --git a/src/bloom.cpp b/src/bloom.cpp
new file mode 100644
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+++ b/src/bloom.cpp
@@ -0,0 +1,133 @@
+// Copyright (c) 2012 The Bitcoin developers
+// Distributed under the MIT/X11 software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+#include <math.h>
+#include <stdlib.h>
+
+#include "bloom.h"
+#include "main.h"
+#include "script.h"
+
+#define LN2SQUARED 0.4804530139182014246671025263266649717305529515945455
+#define LN2 0.6931471805599453094172321214581765680755001343602552
+
+using namespace std;
+
+static const unsigned char bit_mask[8] = {0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80};
+
+CBloomFilter::CBloomFilter(unsigned int nElements, double nFPRate) :
+// The ideal size for a bloom filter with a given number of elements and false positive rate is:
+// - nElements * log(fp rate) / ln(2)^2
+// We ignore filter parameters which will create a bloom filter larger than the protocol limits
+vData(min((unsigned int)(-1 / LN2SQUARED * nElements * log(nFPRate)), MAX_BLOOM_FILTER_SIZE * 8) / 8),
+// The ideal number of hash functions is filter size * ln(2) / number of elements
+// Again, we ignore filter parameters which will create a bloom filter with more hash functions than the protocol limits
+// See http://en.wikipedia.org/wiki/Bloom_filter for an explanation of these formulas
+nHashFuncs(min((unsigned int)(vData.size() * 8 / nElements * LN2), MAX_HASH_FUNCS))
+{
+}
+
+inline unsigned int CBloomFilter::Hash(unsigned int nHashNum, const std::vector<unsigned char>& vDataToHash) const
+{
+ // 0xFBA4C795 chosen as it guarantees a reasonable bit difference between nHashNum values.
+ return MurmurHash3(nHashNum * 0xFBA4C795, vDataToHash) % (vData.size() * 8);
+}
+
+void CBloomFilter::insert(const vector<unsigned char>& vKey)
+{
+ for (unsigned int i = 0; i < nHashFuncs; i++)
+ {
+ unsigned int nIndex = Hash(i, vKey);
+ // Sets bit nIndex of vData
+ vData[nIndex >> 3] |= bit_mask[7 & nIndex];
+ }
+}
+
+void CBloomFilter::insert(const COutPoint& outpoint)
+{
+ CDataStream stream(SER_NETWORK, PROTOCOL_VERSION);
+ stream << outpoint;
+ vector<unsigned char> data(stream.begin(), stream.end());
+ insert(data);
+}
+
+void CBloomFilter::insert(const uint256& hash)
+{
+ vector<unsigned char> data(hash.begin(), hash.end());
+ insert(data);
+}
+
+bool CBloomFilter::contains(const vector<unsigned char>& vKey) const
+{
+ for (unsigned int i = 0; i < nHashFuncs; i++)
+ {
+ unsigned int nIndex = Hash(i, vKey);
+ // Checks bit nIndex of vData
+ if (!(vData[nIndex >> 3] & bit_mask[7 & nIndex]))
+ return false;
+ }
+ return true;
+}
+
+bool CBloomFilter::contains(const COutPoint& outpoint) const
+{
+ CDataStream stream(SER_NETWORK, PROTOCOL_VERSION);
+ stream << outpoint;
+ vector<unsigned char> data(stream.begin(), stream.end());
+ return contains(data);
+}
+
+bool CBloomFilter::contains(const uint256& hash) const
+{
+ vector<unsigned char> data(hash.begin(), hash.end());
+ return contains(data);
+}
+
+bool CBloomFilter::IsWithinSizeConstraints() const
+{
+ return vData.size() <= MAX_BLOOM_FILTER_SIZE && nHashFuncs <= MAX_HASH_FUNCS;
+}
+
+bool CBloomFilter::IsTransactionRelevantToFilter(const CTransaction& tx) const
+{
+ // Match if the filter contains the hash of tx
+ // for finding tx when they appear in a block
+ if (contains(tx.GetHash()))
+ return true;
+
+ BOOST_FOREACH(const CTxOut& txout, tx.vout)
+ {
+ // Match if the filter contains any arbitrary script data element in any scriptPubKey in tx
+ CScript::const_iterator pc = txout.scriptPubKey.begin();
+ vector<unsigned char> data;
+ while (pc < txout.scriptPubKey.end())
+ {
+ opcodetype opcode;
+ if (!txout.scriptPubKey.GetOp(pc, opcode, data))
+ break;
+ if (data.size() != 0 && contains(data))
+ return true;
+ }
+ }
+
+ BOOST_FOREACH(const CTxIn& txin, tx.vin)
+ {
+ // Match if the filter contains an outpoint tx spends
+ if (contains(txin.prevout))
+ return true;
+
+ // Match if the filter contains any arbitrary script data element in any scriptSig in tx
+ CScript::const_iterator pc = txin.scriptSig.begin();
+ vector<unsigned char> data;
+ while (pc < txin.scriptSig.end())
+ {
+ opcodetype opcode;
+ if (!txin.scriptSig.GetOp(pc, opcode, data))
+ break;
+ if (data.size() != 0 && contains(data))
+ return true;
+ }
+ }
+
+ return false;
+}