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Simplify bisection->cellid code by counting bits not depth

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This commit is contained in:
Patrick Niklaus 2017-03-06 23:54:38 +00:00 committed by Patrick Niklaus
parent a92fa257af
commit 821351f56e
1 changed files with 18 additions and 17 deletions
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35
src/partition/bisection_to_partition.cpp
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@ -11,16 +11,11 @@ struct CellBisection
{
std::uint32_t begin;
std::uint32_t end;
std::uint8_t depth;
std::uint8_t bit;
bool tabu; // we will not attempt to split this cell anymore
};
static constexpr std::size_t NUM_BISECTION_BITS = sizeof(BisectionID) * CHAR_BIT;
bool getSide(std::uint8_t depth, BisectionID id)
{
return id & (1ULL << (NUM_BISECTION_BITS - 1 - depth));
}
std::vector<std::uint32_t> getLargeCells(const std::size_t max_cell_size,
const std::vector<CellBisection> &cells)
{
@ -62,7 +57,7 @@ void partitionLevel(const std::vector<BisectionID> &node_to_bisection_id,
for (const auto cell_index : large_cells)
{
auto &cell = cells[cell_index];
BOOST_ASSERT(cell.depth < NUM_BISECTION_BITS);
BOOST_ASSERT(cell.bit < NUM_BISECTION_BITS);
// Go over all nodes and sum up the bits to determine at which position the first one
// bit is
@ -73,8 +68,10 @@ void partitionLevel(const std::vector<BisectionID> &node_to_bisection_id,
[&node_to_bisection_id](const BisectionID lhs, const NodeID rhs) {
return lhs | node_to_bisection_id[rhs];
});
// masks all bit strictly higher then cell.depth
const BisectionID mask = (1ULL << (NUM_BISECTION_BITS - cell.depth)) - 1;
// masks all bit strictly higher then cell.bit
BOOST_ASSERT(sizeof(unsigned long long)*CHAR_BIT > sizeof(BisectionID)*CHAR_BIT);
const BisectionID mask = (1ULL << (cell.bit + 1)) - 1;
BOOST_ASSERT(mask == 0 || util::msb(mask) == cell.bit);
const auto masked_sum = sum & mask;
// we can't split the cell anymore, but it also doesn't conform to the max size
// constraint
@ -84,25 +81,29 @@ void partitionLevel(const std::vector<BisectionID> &node_to_bisection_id,
cell.tabu = true;
continue;
}
const auto msb = util::msb(sum & mask);
// depth counts from MSB to LSB
const auto depth = NUM_BISECTION_BITS - 1 - msb;
const auto bit = util::msb(masked_sum);
// determines if an bisection ID is on the left side of the partition
const BisectionID is_left_mask = 1ULL << bit;
BOOST_ASSERT(util::msb(is_left_mask) == bit);
std::uint32_t middle =
std::partition(permutation.begin() + cell.begin,
permutation.begin() + cell.end,
[depth, &node_to_bisection_id](const auto node_id) {
return getSide(depth, node_to_bisection_id[node_id]);
[is_left_mask, &node_to_bisection_id](const auto node_id) {
return node_to_bisection_id[node_id] & is_left_mask;
}) -
permutation.begin();
cell.depth = depth + 1;
if (bit > 0)
cell.bit = bit - 1;
else
cell.tabu = true;
if (middle != cell.begin && middle != cell.end)
{
auto old_end = cell.end;
cell.end = middle;
cells.push_back(
CellBisection{middle, old_end, static_cast<std::uint8_t>(depth + 1), false});
CellBisection{middle, old_end, static_cast<std::uint8_t>(cell.bit), cell.tabu});
}
}
}
@ -120,7 +121,7 @@ bisectionToPartition(const std::vector<BisectionID> &node_to_bisection_id,
std::vector<CellBisection> cells;
cells.push_back(
CellBisection{0, static_cast<std::uint32_t>(node_to_bisection_id.size()), 0, false});
CellBisection{0, static_cast<std::uint32_t>(node_to_bisection_id.size()), NUM_BISECTION_BITS-1, false});
std::vector<Partition> partitions(max_cell_sizes.size());
std::vector<std::uint32_t> num_cells(max_cell_sizes.size());