bitcoin/src/bloom.cpp

// 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::IsRelevantAndUpdate(const CTransaction& tx, const uint256& hash)
{
    bool fFound = false;
    // Match if the filter contains the hash of tx
    //  for finding tx when they appear in a block
    if (contains(hash))
        fFound = true;

    for (unsigned int i = 0; i < tx.vout.size(); i++)
    {
        const CTxOut& txout = tx.vout[i];
        // Match if the filter contains any arbitrary script data element in any scriptPubKey in tx
        // If this matches, also add the specific output that was matched.
        // This means clients don't have to update the filter themselves when a new relevant tx 
        // is discovered in order to find spending transactions, which avoids round-tripping and race conditions.
        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))
            {
                fFound = true;
                insert(COutPoint(hash, i));
                break;
            }
        }
    }

    if (fFound)
        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;
}