Module: ppl/ppl Branch: pip Commit: 353f9b79d1079e7485f904d5ddacbdafc5195a10 URL: http://www.cs.unipr.it/git/gitweb.cgi?p=ppl/ppl.git;a=commit;h=353f9b79d1079... Author: Enea Zaffanella <zaffanella@cs.unipr.it> Date: Sun Jan 31 16:19:41 2010 +0100 Further optimization to helper function column_lower(). --- src/PIP_Tree.cc | 55 ++++++++++++++++++++++++++++++++++--------------------- 1 files changed, 34 insertions(+), 21 deletions(-) diff --git a/src/PIP_Tree.cc b/src/PIP_Tree.cc index 8a3fad3..a7c173b 100644 --- a/src/PIP_Tree.cc +++ b/src/PIP_Tree.cc @@ -152,36 +152,49 @@ column_lower(const Matrix& tableau, return lhs_coeff > rhs_coeff; } - PPL_DIRTY_TEMP_COEFFICIENT(cij_a); - PPL_DIRTY_TEMP_COEFFICIENT(cij_b); PPL_DIRTY_TEMP_COEFFICIENT(lhs); PPL_DIRTY_TEMP_COEFFICIENT(rhs); const dimension_type num_vars = mapping.size(); dimension_type k = 0; - do { + // While loop guard is: (k < num_rows && lhs == rhs). + // Return value is false, if k >= num_rows; lhs < rhs, otherwise. + // Try to optimize the computation of lhs and rhs. + while (true) { const dimension_type mk = mapping[k]; - if (basis[k]) { + const bool in_base = basis[k]; + if (++k >= num_vars) + return false; + if (in_base) { // Reconstitute the identity submatrix part of tableau. - cij_a = (mk == ja) ? 1 : 0; - cij_b = (mk == jb) ? 1 : 0; + if (mk == ja) { + // Optimizing for: lhs == lhs_coeff && rhs == 0; + if (lhs_coeff == 0) + continue; + else + return lhs_coeff > 0; + } + if (mk == jb) { + // Optimizing for: lhs == 0 && rhs == rhs_coeff; + if (rhs_coeff == 0) + continue; + else + return 0 > rhs_coeff; + } + // Optimizing for: lhs == 0 && rhs == 0; + continue; } else { + // Not in base. const Row& t_mk = tableau[mk]; - cij_a = t_mk[ja]; - cij_b = t_mk[jb]; + lhs = lhs_coeff * t_mk[ja]; + rhs = rhs_coeff * t_mk[jb]; + if (lhs == rhs) + continue; + else + return lhs > rhs; } - ++k; - // Optimizing computation of while guard (and return value): - // (k < num_vars && cij_a * cst_a * sij_b == cij_b * cst_b * sij_a) - if (k == num_vars) - return false; - lhs = cij_a * lhs_coeff; - rhs = cij_b * rhs_coeff; - } while (lhs == rhs); - - // Optimizing computation of return value: - // return k < num_vars && cij_a * cst_a * sij_b > cij_b * cst_b * sij_a; - assert(k < num_vars); - return lhs > rhs; + } + // This point should be unreachable. + throw std::runtime_error("PPL internal error"); } /* Find the column j in revised simplex tableau such as