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Replace std::pow with integer exponent #13321

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bangerth opened this issue Feb 1, 2022 · 7 comments · Fixed by #16449
Closed

Replace std::pow with integer exponent #13321

bangerth opened this issue Feb 1, 2022 · 7 comments · Fixed by #16449
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Starter project
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Release 9.6

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@bangerth
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bangerth commented Feb 1, 2022

A possibly surprising realization from geodynamics/aspect#4456 is that std::pow(x,p) with fixed integer exponent p is vastly more expensive than just writing out the product, at least for relatively small integers p. We should take a look at our code base and see whether there is something that's worth replacing. These 108 places might be a good starting point to look at:

> egrep -r 'std::pow.*[2345](\.0)?\)' include/ source/ examples/
include/deal.II/optimization/line_minimization.h:   *     const double f = 100. * std::pow(x, 4) + std::pow(1. - x, 2); // Value
include/deal.II/optimization/line_minimization.h:   *     const double g = 400. * std::pow(x, 3) - 2. * (1. - x); // Gradient
include/deal.II/optimization/line_minimization.h:      std::pow(x2_shift * x3_shift, 2) * (x2_shift - x3_shift);
include/deal.II/optimization/line_minimization.h:      (r1 * std::pow(x3_shift, 2) - r2 * std::pow(x2_shift, 2)) / denom;
include/deal.II/optimization/line_minimization.h:      (r2 * std::pow(x2_shift, 3) - r1 * std::pow(x3_shift, 3)) / denom;
include/deal.II/grid/reference_cell.h:         {{Point<dim>(-std::pow(1.0 / 3.0, 1.0 / 4.0),
include/deal.II/grid/reference_cell.h:                      +std::pow(1.0 / 3.0, 1.0 / 4.0),
include/deal.II/grid/reference_cell.h:           Point<dim>(-std::pow(1.0 / 3.0, 1.0 / 4.0),
include/deal.II/grid/reference_cell.h:                      +std::pow(1.0 / 3.0, 1.0 / 4.0))}}}};
source/fe/fe_nedelec.cc:        return 1.e-15 * std::exp(std::pow(p, 1.075));
source/base/function_lib_cutoff.cc:                          (-2.0 * r * r / std::pow(-r * r + d * d, 2.0) * d *
source/base/flow_function.cc:            const double rl1 = std::pow(r2, lambda / 2. - .5);
source/base/flow_function.cc:            const double rl1  = std::pow(r2, lambda / 2. - .5);
source/base/data_out_base.cc:        std::sqrt(std::pow(gradient[0], 2.0) + std::pow(gradient[1], 2.0));
source/base/data_out_base.cc:                                    std::pow(nrml[i * d1 + j * d2](2), 2.));
source/base/quadrature_lib.cc:        std::pow((eta_bar * eta_star + std::abs(eta_star)), 1.0 / 3.0) +
source/base/quadrature_lib.cc:        std::pow((eta_bar * eta_star - std::abs(eta_star)), 1.0 / 3.0) +
source/base/quadrature_lib.cc:      double eta   = (std::pow(gamma - gamma_bar, 3.0) +
source/base/function_lib.cc:    return std::pow(r_squared, .25) * std::sin(.5 * phi);
source/base/function_lib.cc:        values[i] = std::pow(r_squared, .25) * std::sin(.5 * phi);
source/base/function_lib.cc:        values[i](0) = std::pow(r_squared, .25) * std::sin(.5 * phi);
source/base/function_lib.cc:    return std::pow(r_squared, .125) * std::sin(.25 * phi);
source/base/function_lib.cc:        values[i] = std::pow(r_squared, .125) * std::sin(.25 * phi);
source/base/function_lib.cc:        values[i](0) = std::pow(r_squared, .125) * std::sin(.25 * phi);
source/base/function_signed_distance.cc:          std::pow(distance, 3);
source/base/function_signed_distance.cc:        val += std::pow((point[d] - center[d]) / radii[d], 2);
source/base/function_signed_distance.cc:          const double ex = (a * a - b * b) * std::pow(std::cos(t), 3) / a;
source/base/function_signed_distance.cc:          const double ey = (b * b - a * a) * std::pow(std::sin(t), 3) / b;
source/numerics/derivative_approximation.cc:        (std::pow(s[0][0], 3) + std::pow(s[1][1], 3) + std::pow(s[2][2], 3) +
source/grid/grid_generator.cc:                  (0.2969 * std::pow(x, 0.5) - 0.126 * x -
source/grid/grid_generator.cc:                   0.3516 * std::pow(x, 2) + 0.2843 * std::pow(x, 3) -
source/grid/grid_generator.cc:                   0.1036 * std::pow(x, 4)); // half thickness at a position x
source/grid/grid_generator.cc:                  (x <= p) ? m / std::pow(p, 2) * (2 * p * x - std::pow(x, 2)) :
source/grid/grid_generator.cc:                             m / std::pow(1 - p, 2) *
source/grid/grid_generator.cc:                               ((1 - 2 * p) + 2 * p * x - std::pow(x, 2));
source/grid/grid_generator.cc:                                      2 * m / std::pow(p, 2) * (p - x) :
source/grid/grid_generator.cc:                                      2 * m / std::pow(1 - p, 2) * (p - x);
source/grid/grid_generator.cc:                  (0.2969 * std::pow(x, 0.5) - 0.126 * x -
source/grid/grid_generator.cc:                   0.3516 * std::pow(x, 2) + 0.2843 * std::pow(x, 3) -
source/grid/grid_generator.cc:                   0.1036 * std::pow(x, 4)); // half thickness at a position x
source/grid/manifold_lib.cc:  double w     = std::sqrt(std::pow(y - std::sin(phi) * R, 2.0) +
source/grid/manifold_lib.cc:                       std::pow(x - std::cos(phi) * R, 2.0) + z * z) /
examples/step-85/step-85.cc:                  std::pow(error_at_point, 2) * fe_values->JxW(q);
examples/step-47/step-47.cc:        return 4 * std::pow(PI, 4.0) * std::sin(PI * p[0]) *
examples/step-12/step-12.cc:        std::pow(cell->diameter(), 1 + 1.0 * dim / 2);
examples/step-9/step-9.cc:      (std::pow(cell->diameter(), 1 + 1.0 * dim / 2) * gradient.norm());
examples/step-25/step-25.cc:    system_matrix.add(std::pow(time_step * theta, 2), laplace_matrix);
examples/step-25/step-25.cc:    system_matrix.add(std::pow(time_step * theta, 2), tmp_matrix);
examples/step-25/step-25.cc:    system_rhs.add(std::pow(time_step * theta, 2), tmp_vector);
examples/step-25/step-25.cc:    system_rhs.add(std::pow(time_step, 2) * theta * (1 - theta), tmp_vector);
examples/step-25/step-25.cc:    system_rhs.add(std::pow(time_step, 2) * theta, tmp_vector);
examples/step-82/step-82.cc:        return_value = 24.0 * std::pow(p(1) * (1.0 - p(1)), 2) +
examples/step-82/step-82.cc:                       +24.0 * std::pow(p(0) * (1.0 - p(0)), 2) +
examples/step-82/step-82.cc:          24.0 * std::pow(p(1) * (1.0 - p(1)) * p(2) * (1.0 - p(2)), 2) +
examples/step-82/step-82.cc:          24.0 * std::pow(p(0) * (1.0 - p(0)) * p(2) * (1.0 - p(2)), 2) +
examples/step-82/step-82.cc:          24.0 * std::pow(p(0) * (1.0 - p(0)) * p(1) * (1.0 - p(1)), 2) +
examples/step-82/step-82.cc:            std::pow(p(2) * (1.0 - p(2)), 2) +
examples/step-82/step-82.cc:            std::pow(p(1) * (1.0 - p(1)), 2) +
examples/step-82/step-82.cc:            std::pow(p(0) * (1.0 - p(0)), 2);
examples/step-82/step-82.cc:        return_value = std::pow(p(0) * (1.0 - p(0)) * p(1) * (1.0 - p(1)), 2);
examples/step-82/step-82.cc:          (2.0 * p(0) - 6.0 * std::pow(p(0), 2) + 4.0 * std::pow(p(0), 3)) *
examples/step-82/step-82.cc:          std::pow(p(1) * (1.0 - p(1)), 2);
examples/step-82/step-82.cc:          (2.0 * p(1) - 6.0 * std::pow(p(1), 2) + 4.0 * std::pow(p(1), 3)) *
examples/step-82/step-82.cc:          std::pow(p(0) * (1.0 - p(0)), 2);
examples/step-82/step-82.cc:          (2.0 * p(0) - 6.0 * std::pow(p(0), 2) + 4.0 * std::pow(p(0), 3)) *
examples/step-82/step-82.cc:          std::pow(p(1) * (1.0 - p(1)) * p(2) * (1.0 - p(2)), 2);
examples/step-82/step-82.cc:          (2.0 * p(1) - 6.0 * std::pow(p(1), 2) + 4.0 * std::pow(p(1), 3)) *
examples/step-82/step-82.cc:          std::pow(p(0) * (1.0 - p(0)) * p(2) * (1.0 - p(2)), 2);
examples/step-82/step-82.cc:          (2.0 * p(2) - 6.0 * std::pow(p(2), 2) + 4.0 * std::pow(p(2), 3)) *
examples/step-82/step-82.cc:          std::pow(p(0) * (1.0 - p(0)) * p(1) * (1.0 - p(1)), 2);
examples/step-82/step-82.cc:                               std::pow(p(1) * (1.0 - p(1)), 2);
examples/step-82/step-82.cc:          (2.0 * p(0) - 6.0 * std::pow(p(0), 2) + 4.0 * std::pow(p(0), 3)) *
examples/step-82/step-82.cc:          (2.0 * p(1) - 6.0 * std::pow(p(1), 2) + 4.0 * std::pow(p(1), 3));
examples/step-82/step-82.cc:                               std::pow(p(0) * (1.0 - p(0)), 2);
examples/step-82/step-82.cc:          std::pow(p(1) * (1.0 - p(1)) * p(2) * (1.0 - p(2)), 2);
examples/step-82/step-82.cc:          (2.0 * p(0) - 6.0 * std::pow(p(0), 2) + 4.0 * std::pow(p(0), 3)) *
examples/step-82/step-82.cc:          (2.0 * p(1) - 6.0 * std::pow(p(1), 2) + 4.0 * std::pow(p(1), 3)) *
examples/step-82/step-82.cc:          std::pow(p(2) * (1.0 - p(2)), 2);
examples/step-82/step-82.cc:          (2.0 * p(0) - 6.0 * std::pow(p(0), 2) + 4.0 * std::pow(p(0), 3)) *
examples/step-82/step-82.cc:          (2.0 * p(2) - 6.0 * std::pow(p(2), 2) + 4.0 * std::pow(p(2), 3)) *
examples/step-82/step-82.cc:          std::pow(p(1) * (1.0 - p(1)), 2);
examples/step-82/step-82.cc:          std::pow(p(0) * (1.0 - p(0)) * p(2) * (1.0 - p(2)), 2);
examples/step-82/step-82.cc:          (2.0 * p(1) - 6.0 * std::pow(p(1), 2) + 4.0 * std::pow(p(1), 3)) *
examples/step-82/step-82.cc:          (2.0 * p(2) - 6.0 * std::pow(p(2), 2) + 4.0 * std::pow(p(2), 3)) *
examples/step-82/step-82.cc:          std::pow(p(0) * (1.0 - p(0)), 2);
examples/step-82/step-82.cc:          std::pow(p(0) * (1.0 - p(0)) * p(1) * (1.0 - p(1)), 2);
examples/step-82/step-82.cc:              1.0 / std::pow(face->diameter(), 3); // ĥ_e^{-3}
examples/step-82/step-82.cc:              1.0 / std::pow(face->diameter(), 3); // h^{-3}
examples/step-82/step-82.cc:                                std::pow(u_exact_q - solution_values[q], 2) *
examples/step-82/step-82.cc:                                std::pow(u_exact_q - solution_values[q], 2) *
examples/step-62/step-62.cc:                   std::exp(-(std::pow(p[0] - force_center[0], 2) /
examples/step-62/step-62.cc:                                (2 * std::pow(force_sigma_x, 2)) +
examples/step-62/step-62.cc:                              std::pow(p[1] - force_center[1], 2) /
examples/step-62/step-62.cc:                                (2 * std::pow(force_sigma_y, 2))));
examples/step-62/step-62.cc:                      matrix_sum += -std::pow(omega, 2) *
examples/step-55/step-55.cc:                0.1 * std::pow(-std::sqrt(25.0 + 4 * pi2) + 5.0, 2) *
examples/step-55/step-55.cc:                0.05 * std::pow(-std::sqrt(25.0 + 4 * pi2) + 5.0, 3) *
examples/step-71/step-71.cc:        std::pow(1.0 / std::cosh(two_h_dot_h_div_h_sat_squ), 2.0);
examples/step-71/step-71.cc:                                std::pow(det_F, -2.0 / dim - 2.0) * ddet_F_dC) +
examples/step-4/step-4.cc:    return_value += 4.0 * std::pow(p(i), 4.0);
examples/step-30/step-30.cc:        std::pow(cell->diameter(), 1 + 1.0 * dim / 2);
examples/step-76/step-76.cc:  const double courant_number = 0.15 / std::pow(fe_degree, 1.5);
examples/step-12b/step-12b.cc:        std::pow(cell->diameter(), 1 + 1.0 * dim / 2);
examples/step-43/step-43.cc:    const double denominator = std::pow(temp, 2.0);
examples/step-44/step-44.cc:              std::pow((det_F_qp - J_tilde_qp), 2);
examples/step-67/step-67.cc:  const double courant_number = 0.15 / std::pow(fe_degree, 1.5);
examples/step-53/step-53.cc:      std::atan2(x(2) + ep * ep * b * std::pow(std::sin(th), 3),
examples/step-53/step-53.cc:                  (ellipticity * ellipticity * R * std::pow(std::cos(th), 3))));
@Rombur
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Rombur commented Feb 1, 2022

Which optimization flags are you passing to the compiler? With -O3, gcc generates the same code but the code is different if you use -O0 https://godbolt.org/z/bz3bsn33K

@bangerth
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bangerth commented Feb 1, 2022

I used whatever release mode gave me. But you already get different answers if p=3.

@bangerth
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bangerth commented Feb 1, 2022

Here is a better regex:

> egrep -r 'std::pow.*, [2345](\.0)?\)' include/ source/ examples/
include/deal.II/optimization/line_minimization.h:   *     const double f = 100. * std::pow(x, 4) + std::pow(1. - x, 2); // Value
include/deal.II/optimization/line_minimization.h:   *     const double g = 400. * std::pow(x, 3) - 2. * (1. - x); // Gradient
include/deal.II/optimization/line_minimization.h:      std::pow(x2_shift * x3_shift, 2) * (x2_shift - x3_shift);
include/deal.II/optimization/line_minimization.h:      (r1 * std::pow(x3_shift, 2) - r2 * std::pow(x2_shift, 2)) / denom;
include/deal.II/optimization/line_minimization.h:      (r2 * std::pow(x2_shift, 3) - r1 * std::pow(x3_shift, 3)) / denom;
source/base/function_lib_cutoff.cc:                          (-2.0 * r * r / std::pow(-r * r + d * d, 2.0) * d *
source/base/data_out_base.cc:        std::sqrt(std::pow(gradient[0], 2.0) + std::pow(gradient[1], 2.0));
source/base/quadrature_lib.cc:      double eta   = (std::pow(gamma - gamma_bar, 3.0) +
source/base/function_signed_distance.cc:          std::pow(distance, 3);
source/base/function_signed_distance.cc:        val += std::pow((point[d] - center[d]) / radii[d], 2);
source/base/function_signed_distance.cc:          const double ex = (a * a - b * b) * std::pow(std::cos(t), 3) / a;
source/base/function_signed_distance.cc:          const double ey = (b * b - a * a) * std::pow(std::sin(t), 3) / b;
source/numerics/derivative_approximation.cc:        (std::pow(s[0][0], 3) + std::pow(s[1][1], 3) + std::pow(s[2][2], 3) +
source/grid/grid_generator.cc:                   0.3516 * std::pow(x, 2) + 0.2843 * std::pow(x, 3) -
source/grid/grid_generator.cc:                   0.1036 * std::pow(x, 4)); // half thickness at a position x
source/grid/grid_generator.cc:                  (x <= p) ? m / std::pow(p, 2) * (2 * p * x - std::pow(x, 2)) :
source/grid/grid_generator.cc:                             m / std::pow(1 - p, 2) *
source/grid/grid_generator.cc:                               ((1 - 2 * p) + 2 * p * x - std::pow(x, 2));
source/grid/grid_generator.cc:                                      2 * m / std::pow(p, 2) * (p - x) :
source/grid/grid_generator.cc:                                      2 * m / std::pow(1 - p, 2) * (p - x);
source/grid/grid_generator.cc:                   0.3516 * std::pow(x, 2) + 0.2843 * std::pow(x, 3) -
source/grid/grid_generator.cc:                   0.1036 * std::pow(x, 4)); // half thickness at a position x
source/grid/manifold_lib.cc:  double w     = std::sqrt(std::pow(y - std::sin(phi) * R, 2.0) +
source/grid/manifold_lib.cc:                       std::pow(x - std::cos(phi) * R, 2.0) + z * z) /
examples/step-85/step-85.cc:                  std::pow(error_at_point, 2) * fe_values->JxW(q);
examples/step-47/step-47.cc:        return 4 * std::pow(PI, 4.0) * std::sin(PI * p[0]) *
examples/step-25/step-25.cc:    system_matrix.add(std::pow(time_step * theta, 2), laplace_matrix);
examples/step-25/step-25.cc:    system_matrix.add(std::pow(time_step * theta, 2), tmp_matrix);
examples/step-25/step-25.cc:    system_rhs.add(std::pow(time_step * theta, 2), tmp_vector);
examples/step-25/step-25.cc:    system_rhs.add(std::pow(time_step, 2) * theta * (1 - theta), tmp_vector);
examples/step-25/step-25.cc:    system_rhs.add(std::pow(time_step, 2) * theta, tmp_vector);
examples/step-82/step-82.cc:        return_value = 24.0 * std::pow(p(1) * (1.0 - p(1)), 2) +
examples/step-82/step-82.cc:                       +24.0 * std::pow(p(0) * (1.0 - p(0)), 2) +
examples/step-82/step-82.cc:          24.0 * std::pow(p(1) * (1.0 - p(1)) * p(2) * (1.0 - p(2)), 2) +
examples/step-82/step-82.cc:          24.0 * std::pow(p(0) * (1.0 - p(0)) * p(2) * (1.0 - p(2)), 2) +
examples/step-82/step-82.cc:          24.0 * std::pow(p(0) * (1.0 - p(0)) * p(1) * (1.0 - p(1)), 2) +
examples/step-82/step-82.cc:            std::pow(p(2) * (1.0 - p(2)), 2) +
examples/step-82/step-82.cc:            std::pow(p(1) * (1.0 - p(1)), 2) +
examples/step-82/step-82.cc:            std::pow(p(0) * (1.0 - p(0)), 2);
examples/step-82/step-82.cc:        return_value = std::pow(p(0) * (1.0 - p(0)) * p(1) * (1.0 - p(1)), 2);
examples/step-82/step-82.cc:          (2.0 * p(0) - 6.0 * std::pow(p(0), 2) + 4.0 * std::pow(p(0), 3)) *
examples/step-82/step-82.cc:          std::pow(p(1) * (1.0 - p(1)), 2);
examples/step-82/step-82.cc:          (2.0 * p(1) - 6.0 * std::pow(p(1), 2) + 4.0 * std::pow(p(1), 3)) *
examples/step-82/step-82.cc:          std::pow(p(0) * (1.0 - p(0)), 2);
examples/step-82/step-82.cc:          (2.0 * p(0) - 6.0 * std::pow(p(0), 2) + 4.0 * std::pow(p(0), 3)) *
examples/step-82/step-82.cc:          std::pow(p(1) * (1.0 - p(1)) * p(2) * (1.0 - p(2)), 2);
examples/step-82/step-82.cc:          (2.0 * p(1) - 6.0 * std::pow(p(1), 2) + 4.0 * std::pow(p(1), 3)) *
examples/step-82/step-82.cc:          std::pow(p(0) * (1.0 - p(0)) * p(2) * (1.0 - p(2)), 2);
examples/step-82/step-82.cc:          (2.0 * p(2) - 6.0 * std::pow(p(2), 2) + 4.0 * std::pow(p(2), 3)) *
examples/step-82/step-82.cc:          std::pow(p(0) * (1.0 - p(0)) * p(1) * (1.0 - p(1)), 2);
examples/step-82/step-82.cc:                               std::pow(p(1) * (1.0 - p(1)), 2);
examples/step-82/step-82.cc:          (2.0 * p(0) - 6.0 * std::pow(p(0), 2) + 4.0 * std::pow(p(0), 3)) *
examples/step-82/step-82.cc:          (2.0 * p(1) - 6.0 * std::pow(p(1), 2) + 4.0 * std::pow(p(1), 3));
examples/step-82/step-82.cc:                               std::pow(p(0) * (1.0 - p(0)), 2);
examples/step-82/step-82.cc:          std::pow(p(1) * (1.0 - p(1)) * p(2) * (1.0 - p(2)), 2);
examples/step-82/step-82.cc:          (2.0 * p(0) - 6.0 * std::pow(p(0), 2) + 4.0 * std::pow(p(0), 3)) *
examples/step-82/step-82.cc:          (2.0 * p(1) - 6.0 * std::pow(p(1), 2) + 4.0 * std::pow(p(1), 3)) *
examples/step-82/step-82.cc:          std::pow(p(2) * (1.0 - p(2)), 2);
examples/step-82/step-82.cc:          (2.0 * p(0) - 6.0 * std::pow(p(0), 2) + 4.0 * std::pow(p(0), 3)) *
examples/step-82/step-82.cc:          (2.0 * p(2) - 6.0 * std::pow(p(2), 2) + 4.0 * std::pow(p(2), 3)) *
examples/step-82/step-82.cc:          std::pow(p(1) * (1.0 - p(1)), 2);
examples/step-82/step-82.cc:          std::pow(p(0) * (1.0 - p(0)) * p(2) * (1.0 - p(2)), 2);
examples/step-82/step-82.cc:          (2.0 * p(1) - 6.0 * std::pow(p(1), 2) + 4.0 * std::pow(p(1), 3)) *
examples/step-82/step-82.cc:          (2.0 * p(2) - 6.0 * std::pow(p(2), 2) + 4.0 * std::pow(p(2), 3)) *
examples/step-82/step-82.cc:          std::pow(p(0) * (1.0 - p(0)), 2);
examples/step-82/step-82.cc:          std::pow(p(0) * (1.0 - p(0)) * p(1) * (1.0 - p(1)), 2);
examples/step-82/step-82.cc:              1.0 / std::pow(face->diameter(), 3); // ĥ_e^{-3}
examples/step-82/step-82.cc:              1.0 / std::pow(face->diameter(), 3); // h^{-3}
examples/step-82/step-82.cc:                                std::pow(u_exact_q - solution_values[q], 2) *
examples/step-82/step-82.cc:                                std::pow(u_exact_q - solution_values[q], 2) *
examples/step-62/step-62.cc:                   std::exp(-(std::pow(p[0] - force_center[0], 2) /
examples/step-62/step-62.cc:                                (2 * std::pow(force_sigma_x, 2)) +
examples/step-62/step-62.cc:                              std::pow(p[1] - force_center[1], 2) /
examples/step-62/step-62.cc:                                (2 * std::pow(force_sigma_y, 2))));
examples/step-62/step-62.cc:                      matrix_sum += -std::pow(omega, 2) *
examples/step-55/step-55.cc:                0.1 * std::pow(-std::sqrt(25.0 + 4 * pi2) + 5.0, 2) *
examples/step-55/step-55.cc:                0.05 * std::pow(-std::sqrt(25.0 + 4 * pi2) + 5.0, 3) *
examples/step-71/step-71.cc:        std::pow(1.0 / std::cosh(two_h_dot_h_div_h_sat_squ), 2.0);
examples/step-4/step-4.cc:    return_value += 4.0 * std::pow(p(i), 4.0);
examples/step-43/step-43.cc:    const double denominator = std::pow(temp, 2.0);
examples/step-44/step-44.cc:              std::pow((det_F_qp - J_tilde_qp), 2);
examples/step-53/step-53.cc:      std::atan2(x(2) + ep * ep * b * std::pow(std::sin(th), 3),
examples/step-53/step-53.cc:                  (ellipticity * ellipticity * R * std::pow(std::cos(th), 3))));

@bangerth bangerth mentioned this issue Feb 1, 2022
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@Rombur
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Rombur commented Feb 1, 2022

If you use p >= 3, you need to use ffast-math. It works at least up to pow(x, 8). It might have unwanted effect though.

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blaisb commented Feb 1, 2022

That's funny, I thought this was automatic (at least for n =2,3,4). I thought this was only an issue if you made the mistake of writing std::pow(x,2.) instead of std::pow(x,2)...

@marcfehling
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IIRC, we have Utilities::fixed_power (7c9f785) and Utilities::pow (#9764) that should be faster than std::pow.

@Darth-Veidim Darth-Veidim mentioned this issue Feb 6, 2023
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@bangerth bangerth mentioned this issue Jan 5, 2024
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@bangerth bangerth added this to the Release 9.6 milestone Jan 5, 2024
This was referenced Jan 9, 2024
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bangerth commented Jan 9, 2024

Current state: The egrep expression only triggers for two more places. One is in step-4, where I would like to avoid the complication of having to explain why we use the function; the other is in step-82, and that change is currently stuck behind #16440.

So the only thing left to finish this is the change to step-82, which will require the following regex replace:

perl -pi -e 's/std::pow\(([^,]*), ([2345])(\.0?)?\)/Utilities::fixed_power<\2>(\1)/g;' examples/step-82/step-82.cc

This was referenced Jan 10, 2024
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Use Utilities::fixed_power() in step-82. bangerth/dealii
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@Rombur @bangerth @blaisb @marcfehling