From ac7c9600671322847fcce2089d43736112ff3dc2 Mon Sep 17 00:00:00 2001
From: Gregory Maxwell <greg@xiph.org>
Date: Sun, 18 Aug 2013 20:21:06 -0700
Subject: Performance optimization for bloom filters.

This reduces a peer's ability to attack network resources by
 using a full bloom filter, but without reducing the usability
 of bloom filters.  It sets a default match everything filter
 for peers and it generalizes a prior optimization to
 cover more cases.
---
 src/bloom.cpp | 26 ++++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

(limited to 'src/bloom.cpp')

diff --git a/src/bloom.cpp b/src/bloom.cpp
index d9ec2efa81..6bdffdbb38 100644
--- a/src/bloom.cpp
+++ b/src/bloom.cpp
@@ -23,6 +23,8 @@ vData(min((unsigned int)(-1  / LN2SQUARED * nElements * log(nFPRate)), MAX_BLOOM
 // 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
+isFull(false),
+isEmpty(false),
 nHashFuncs(min((unsigned int)(vData.size() * 8 / nElements * LN2), MAX_HASH_FUNCS)),
 nTweak(nTweakIn),
 nFlags(nFlagsIn)
@@ -37,7 +39,7 @@ inline unsigned int CBloomFilter::Hash(unsigned int nHashNum, const std::vector<
 
 void CBloomFilter::insert(const vector<unsigned char>& vKey)
 {
-    if (vData.size() == 1 && vData[0] == 0xff)
+    if (isFull)
         return;
     for (unsigned int i = 0; i < nHashFuncs; i++)
     {
@@ -45,6 +47,7 @@ void CBloomFilter::insert(const vector<unsigned char>& vKey)
         // Sets bit nIndex of vData
         vData[nIndex >> 3] |= bit_mask[7 & nIndex];
     }
+    isEmpty = false;
 }
 
 void CBloomFilter::insert(const COutPoint& outpoint)
@@ -63,8 +66,10 @@ void CBloomFilter::insert(const uint256& hash)
 
 bool CBloomFilter::contains(const vector<unsigned char>& vKey) const
 {
-    if (vData.size() == 1 && vData[0] == 0xff)
+    if (isFull)
         return true;
+    if (isEmpty)
+        return false;
     for (unsigned int i = 0; i < nHashFuncs; i++)
     {
         unsigned int nIndex = Hash(i, vKey);
@@ -99,6 +104,10 @@ bool CBloomFilter::IsRelevantAndUpdate(const CTransaction& tx, const uint256& ha
     bool fFound = false;
     // Match if the filter contains the hash of tx
     //  for finding tx when they appear in a block
+    if (isFull)
+        return true;
+    if (isEmpty)
+        return false;
     if (contains(hash))
         fFound = true;
 
@@ -158,3 +167,16 @@ bool CBloomFilter::IsRelevantAndUpdate(const CTransaction& tx, const uint256& ha
 
     return false;
 }
+
+void CBloomFilter::UpdateEmptyFull()
+{
+    bool full = true;
+    bool empty = true;
+    for (unsigned int i = 0; i < vData.size(); i++)
+    {
+        full &= vData[i] == 0xff;
+        empty &= vData[i] == 0;
+    }
+    isFull = full;
+    isEmpty = empty;
+}
-- 
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