Add a CBloomFilter class for use as a transaction filter.

src/bloom.h

@@ -0,0 +1,70 @@
+// 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.
+#ifndef BITCOIN_BLOOM_H
+#define BITCOIN_BLOOM_H
+
+#include <vector>
+
+#include "uint256.h"
+#include "serialize.h"
+
+class COutPoint;
+class CTransaction;
+
+// 20,000 items with fp rate < 0.1% or 10,000 items and <0.0001%
+static const unsigned int MAX_BLOOM_FILTER_SIZE = 36000; // bytes
+static const unsigned int MAX_HASH_FUNCS = 50;
+
+
+/**
+ * BloomFilter is a probabilistic filter which SPV clients provide
+ * so that we can filter the transactions we sends them.
+ * 
+ * This allows for significantly more efficient transaction and block downloads.
+ * 
+ * Because bloom filters are probabilistic, an SPV node can increase the false-
+ * positive rate, making us send them transactions which aren't actually theirs, 
+ * allowing clients to trade more bandwidth for more privacy by obfuscating which
+ * keys are owned by them.
+ */
+class CBloomFilter
+{
+private:
+    std::vector<unsigned char> vData;
+    unsigned int nHashFuncs;
+
+    unsigned int Hash(unsigned int nHashNum, const std::vector<unsigned char>& vDataToHash) const;
+
+public:
+    // Creates a new bloom filter which will provide the given fp rate when filled with the given number of elements
+    // Note that if the given parameters will result in a filter outside the bounds of the protocol limits,
+    // the filter created will be as close to the given parameters as possible within the protocol limits.
+    // This will apply if nFPRate is very low or nElements is unreasonably high.
+    CBloomFilter(unsigned int nElements, double nFPRate);
+    // Using a filter initialized with this results in undefined behavior
+    // Should only be used for deserialization
+    CBloomFilter() {}
+
+    IMPLEMENT_SERIALIZE
+    (
+        READWRITE(vData);
+        READWRITE(nHashFuncs);
+    )
+
+    void insert(const std::vector<unsigned char>& vKey);
+    void insert(const COutPoint& outpoint);
+    void insert(const uint256& hash);
+
+    bool contains(const std::vector<unsigned char>& vKey) const;
+    bool contains(const COutPoint& outpoint) const;
+    bool contains(const uint256& hash) const;
+
+    // True if the size is <= MAX_BLOOM_FILTER_SIZE and the number of hash functions is <= MAX_HASH_FUNCS
+    // (catch a filter which was just deserialized which was too big)
+    bool IsWithinSizeConstraints() const;
+
+    bool IsTransactionRelevantToFilter(const CTransaction& tx) const;
+};
+
+#endif /* BITCOIN_BLOOM_H */