Module: ppl/ppl Branch: master Commit: 27a720c897ec87c9854374630e9846d882e86e7b URL: http://www.cs.unipr.it/git/gitweb.cgi?p=ppl/ppl.git;a=commit;h=27a720c897ec8...

Author: Marco Poletti poletti.marco@gmail.com Date: Sun Oct 3 17:13:33 2010 +0200

Sparse_Row: optimize linear_combine(), avoiding the insertion of too many elements.

---

src/Sparse_Row.cc | 164 ++++++++++++++++++++++++++++++++++++++++++++++++++++- 1 files changed, 163 insertions(+), 1 deletions(-)

diff --git a/src/Sparse_Row.cc b/src/Sparse_Row.cc index c3c0f3f..1dec76d 100644 --- a/src/Sparse_Row.cc +++ b/src/Sparse_Row.cc @@ -232,6 +232,107 @@ PPL::Sparse_Row::normalize() { PPL_ASSERT(OK()); }

+namespace { + +class sparse_row_linear_combine_helper_iterator { +public: + sparse_row_linear_combine_helper_iterator( + const PPL::Sparse_Row& x, const PPL::Sparse_Row& y, + PPL::Coefficient_traits::const_reference coeff1_1, + PPL::Coefficient_traits::const_reference coeff2_1) + : coeff1(coeff1_1), coeff2(coeff2_1) { + i = x.begin(); + i_end = x.end(); + j = y.begin(); + j_end = y.end(); + update_current_data(); + } + + void operator++() { + if (from_i) + ++i; + if (from_j) + ++j; + update_current_data(); + } + + PPL::Coefficient_traits::const_reference operator*() { + return current_value; + } + + PPL::dimension_type index() { + return current_index; + } + +private: + void update_current_data() { + if (i == i_end) { + if (j == j_end) { + return; + } else { + // i == i_end, j != j_end, so use j. + current_index = j.index(); + current_value = *j; + current_value *= coeff2; + from_i = false; + from_j = true; + } + } else { + if (j == j_end) { + // i != i_end, j == j_end, so use i. + current_index = i.index(); + current_value = *i; + current_value *= coeff1; + from_i = true; + from_j = false; + } else { + // i != i_end and j != j_end. + if (i.index() < j.index()) { + // i.index() < j.index(), so use i. + current_index = i.index(); + current_value = *i; + current_value *= coeff1; + from_i = true; + from_j = false; + } else { + if (i.index() != j.index()) { + PPL_ASSERT(i.index() > j.index()); + // i.index() > j.index(), so use j. + current_index = j.index(); + current_value = *j; + current_value *= coeff2; + from_i = false; + from_j = true; + } else { + // i.index() == j.index(), so use both i and j. + current_index = i.index(); + current_value = *i; + current_value *= coeff1; + PPL::add_mul_assign(current_value, *j, coeff2); + from_i = true; + from_j = true; + } + } + } + } + PPL_ASSERT(!from_i || i != i_end); + PPL_ASSERT(!from_j || j != j_end); + } + + PPL::Coefficient_traits::const_reference coeff1; + PPL::Coefficient_traits::const_reference coeff2; + PPL::Sparse_Row::const_iterator i; + PPL::Sparse_Row::const_iterator i_end; + PPL::Sparse_Row::const_iterator j; + PPL::Sparse_Row::const_iterator j_end; + PPL::dimension_type current_index; + PPL::Coefficient current_value; + bool from_i; + bool from_j; +}; + +} // namespace + void PPL::Sparse_Row::linear_combine(const Sparse_Row& y, Coefficient_traits::const_reference coeff1, @@ -239,7 +340,9 @@ PPL::Sparse_Row::linear_combine(const Sparse_Row& y, PPL_ASSERT(coeff1 != 0); PPL_ASSERT(coeff2 != 0); PPL_ASSERT(this != &y); + if (coeff1 == 1) { + // Optimize for this special case. iterator i = end(); for (const_iterator j = y.begin(), j_end = y.end(); j != j_end; ++j) { i = insert(i, j.index()); @@ -247,7 +350,45 @@ PPL::Sparse_Row::linear_combine(const Sparse_Row& y, if (*i == 0) i = reset(i); } - } else { + return; + } + + dimension_type counter = 0; + // Count the number of elements that are stored in y but not in *this. + { + iterator i = begin(); + iterator i_end = end(); + const_iterator j = y.begin(); + const_iterator j_end = y.end(); + if (i != i_end) { + while (j != j_end) { + PPL_ASSERT(i != i_end); + if (i.index() == j.index()) { + ++i; + ++j; + if (i == i_end) + break; + } else + if (i.index() < j.index()) { + i = lower_bound(i, j.index()); + if (i == i_end) + break; + } else { + PPL_ASSERT(i.index() > j.index()); + ++counter; + ++j; + } + } + } + PPL_ASSERT(i == i_end || j == j_end); + for ( ; j != j_end; ++j) + ++counter; + } + // This condition is arbitrary. Changing it affects performance but not + // correctness. The values have been tuned using some ppl_lpsol benchmarks + // on 2 October 2010. + if (counter == 0 || counter < 7 * size() / 64) { + // Few insertions needed, do them directly. iterator i = begin(); // This is a const reference to an internal iterator, that is kept valid. // If we just stored a copy, that would be invalidated by the calls to @@ -283,6 +424,27 @@ PPL::Sparse_Row::linear_combine(const Sparse_Row& y, i = insert(i, j.index(), *j); (*i) *= coeff2; } + } else { + // Too many insertions needed, a full copy is probably faster than + // inserting all those new elements into *this. + CO_Tree new_tree(sparse_row_linear_combine_helper_iterator(*this, y, + coeff1, + coeff2), + counter + tree.size()); + std::swap(tree, new_tree); + + // Now remove stored zeroes. + iterator i = begin(); + // Note that end() can not be called only once, because reset() + // invalidates all iterators. + while (i != end()) { + if (*i == 0) { + const dimension_type old_index = i.index(); + i = reset(i); + PPL_ASSERT(find(old_index) == end()); + } else + ++i; + } } }