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Merge pull request #22 from j-berman/match-decoy-selection-algo

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Match Monero 0.17.2.3 decoy selection algo
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Lee *!* Clagett 2022-07-24 20:08:55 -04:00 committed by GitHub
commit ca6fb66aee
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1 changed files with 16 additions and 5 deletions
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21
src/util/gamma_picker.cpp
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@ -40,6 +40,8 @@ namespace lws
constexpr const double gamma_shape = 19.28;
constexpr const double gamma_scale = 1 / double(1.61);
constexpr const std::size_t blocks_in_a_year = (86400 * 365) / DIFFICULTY_TARGET_V2;
constexpr const std::size_t default_unlock_time = CRYPTONOTE_DEFAULT_TX_SPENDABLE_AGE * DIFFICULTY_TARGET_V2;
constexpr const std::size_t recent_spend_window = 15 * DIFFICULTY_TARGET_V2;
}
gamma_picker::gamma_picker(std::vector<uint64_t> rct_offsets)
@ -84,17 +86,26 @@ namespace lws
static_assert(std::is_empty<crypto::random_device>(), "random_device is no longer cheap to construct");
static constexpr const crypto::random_device engine{};
const auto end = offsets().end() - CRYPTONOTE_DEFAULT_TX_SPENDABLE_AGE;
const uint64_t num_rct_outputs = spendable_upper_bound();
for (unsigned tries = 0; tries < 100; ++tries)
{
std::uint64_t output_index = std::exp(gamma(engine)) * outputs_per_second;
if (offsets().back() <= output_index)
double output_age_in_seconds = std::exp(gamma(engine));
// shift output back by unlock time to apply distribution from chain tip
if (output_age_in_seconds > default_unlock_time)
output_age_in_seconds -= default_unlock_time;
else
output_age_in_seconds = crypto::rand_idx(recent_spend_window);
std::uint64_t output_index = output_age_in_seconds * outputs_per_second;
if (num_rct_outputs <= output_index)
continue; // gamma selected older than blockchain height (rare)
output_index = offsets().back() - 1 - output_index;
output_index = num_rct_outputs - 1 - output_index;
const auto selection = std::lower_bound(offsets().begin(), end, output_index);
if (selection == end)
continue; // gamma selected within locked/non-spendable range (rare)
throw std::logic_error{"Unable to select random output - output not found in range (should never happen)"};
const std::uint64_t first_rct = offsets().begin() == selection ? 0 : *(selection - 1);
const std::uint64_t n_rct = *selection - first_rct;
@ -102,7 +113,7 @@ namespace lws
return first_rct + crypto::rand_idx(n_rct);
// block had zero outputs (miner didn't collect XMR?)
}
throw std::runtime_error{"Unable to select random output in spendable range using gamma distribution after 1,024 attempts"};
throw std::runtime_error{"Unable to select random output in spendable range using gamma distribution after 100 attempts"};
}
std::vector<std::uint64_t> gamma_picker::take_offsets()