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Merge pull request #2312 from gmaxwell/random_random

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ApproximateBestSubset internal RNG to prevent degenerate behavior.
This commit is contained in:
Gavin Andresen
2013-02-22 08:57:38 -08:00
parent 1167af7e5c 907a2aa4c7
commit aaeb443791
4 changed files with 111 additions and 13 deletions
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10
src/wallet.cpp
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@@ -984,6 +984,8 @@ static void ApproximateBestSubset(vector<pair<int64, pair<const CWalletTx*,unsig
vfBest.assign(vValue.size(), true);
nBest = nTotalLower;
seed_insecure_rand();
for (int nRep = 0; nRep < iterations && nBest != nTargetValue; nRep++)
{
vfIncluded.assign(vValue.size(), false);
@@ -993,7 +995,13 @@ static void ApproximateBestSubset(vector<pair<int64, pair<const CWalletTx*,unsig
{
for (unsigned int i = 0; i < vValue.size(); i++)
{
if (nPass == 0 ? rand() % 2 : !vfIncluded[i])
//The solver here uses a randomized algorithm,
//the randomness serves no real security purpose but is just
//needed to prevent degenerate behavior and it is important
//that the rng fast. We do not use a constant random sequence,
//because there may be some privacy improvement by making
//the selection random.
if (nPass == 0 ? insecure_rand()&1 : !vfIncluded[i])
{
nTotal += vValue[i].first;
vfIncluded[i] = true;