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fix decoy selection off-by-1

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This commit is contained in:
j-berman 2023-03-24 17:44:01 -07:00
parent 123ee4f159
commit 945abfd57d
1 changed files with 9 additions and 3 deletions

12
src/util/gamma_picker.cpp
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@ -68,14 +68,20 @@ namespace lws
bool gamma_picker::is_valid() const noexcept
{
return CRYPTONOTE_DEFAULT_TX_SPENDABLE_AGE < rct_offsets.size();
return CRYPTONOTE_DEFAULT_TX_SPENDABLE_AGE < rct_offsets.size() + 1;
}
std::uint64_t gamma_picker::spendable_upper_bound() const noexcept
{
if (!is_valid())
return 0;
return *(rct_offsets.end() - CRYPTONOTE_DEFAULT_TX_SPENDABLE_AGE - 1);
return *(rct_offsets.end() - CRYPTONOTE_DEFAULT_TX_SPENDABLE_AGE);
/* Assume block indexes: [0, 1, ..., n-2, n-1]
where n is the number of blocks in the chain
A user can spend an output starting in block index n - CRYPTONOTE_DEFAULT_TX_SPENDABLE_AGE
The total number of spendable outputs is the cumulative count stored at that block
rct_offsets.end() points to index n
Therefore we need to return index rct_offets.end() - CRYPTONOTE_DEFAULT_TX_SPENDABLE_AGE */
}
std::uint64_t gamma_picker::operator()()
@ -85,7 +91,7 @@ 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 auto end = offsets().end() - CRYPTONOTE_DEFAULT_TX_SPENDABLE_AGE + 1;
const uint64_t num_rct_outputs = spendable_upper_bound();
for (unsigned tries = 0; tries < 100; ++tries)