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triangular distribution for mixins #255

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merged 2 commits into from
Apr 5, 2015
Merged

triangular distribution for mixins #255

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f2e8348
triangular distribution to choose recent outputs more often for mixins
iamsmooth Apr 5, 2015
83ddc94
handle unlikely rounding up after sqrt
iamsmooth Apr 5, 2015
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9 changes: 8 additions & 1 deletion src/cryptonote_core/blockchain_storage.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -30,6 +30,7 @@

#include <algorithm>
#include <cstdio>
#include <cmath>
#include <boost/archive/binary_oarchive.hpp>
#include <boost/archive/binary_iarchive.hpp>

Expand Down Expand Up @@ -1081,7 +1082,13 @@ bool blockchain_storage::get_random_outs_for_amounts(const COMMAND_RPC_GET_RANDO
size_t try_count = 0;
for(uint64_t j = 0; j != req.outs_count && try_count < up_index_limit;)
{
size_t i = crypto::rand<size_t>()%up_index_limit;
// triangular distribution over [a,b) with a=0, mode c=b=up_index_limit
uint64_t r = crypto::rand<uint64_t>() % ((uint64_t)1 << 53);
double frac = std::sqrt((double)r / ((uint64_t)1 << 53));
size_t i = (size_t)(frac*up_index_limit);
// just in case rounding up to 1 occurs after sqrt
if (i == up_index_limit)
--i;
if(used.count(i))
continue;
bool added = add_out_to_get_random_outs(amount_outs, result_outs, amount, i);
Expand Down