Add log1p and expm1

Chowdhury-DSP · Dec 23, 2023 · 89af9be · 89af9be
1 parent b5a1108
commit 89af9be
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Showing 4 changed files with 18 additions and 6 deletions.
diff --git a/README.md b/README.md
@@ -5,8 +5,8 @@
 Currently supported:
 
 - sin/cos/tan
-- exp/exp2/exp10
-- log/log2/log10
+- exp/exp2/exp10/expm1
+- log/log2/log10/log1p
 - sinh/cosh/tanh
 - arcsinh
 - sigmoid

diff --git a/include/math_approx/src/log_approx.hpp b/include/math_approx/src/log_approx.hpp
@@ -180,4 +180,10 @@ constexpr T log10 (T x)
 {
     return log<pow_detail::Base10<scalar_of_t<T>>, order, C1_continuous> (x);
 }
+
+template <int order, bool C1_continuous = false, typename T>
+constexpr T log1p (T x)
+{
+    return log<pow_detail::BaseE<scalar_of_t<T>>, order, C1_continuous> ((T) 1 + x);
+}
 }
diff --git a/include/math_approx/src/pow_approx.hpp b/include/math_approx/src/pow_approx.hpp
@@ -216,4 +216,10 @@ constexpr T exp10 (T x)
 {
     return pow<pow_detail::Base10<scalar_of_t<T>>, order, C1_continuous> (x);
 }
+
+template <int order, bool C1_continuous = false, typename T>
+constexpr T expm1 (T x)
+{
+    return pow<pow_detail::BaseE<scalar_of_t<T>>, order, C1_continuous> (x) - (T) 1;
+}
 }
diff --git a/tools/plotter/plotter.cpp b/tools/plotter/plotter.cpp
@@ -62,13 +62,13 @@ int main()
 {
     plt::figure();
     const auto range = std::make_pair (-1.0f, 1.0f);
-    static constexpr auto tol = 1.0e-2f;
+    static constexpr auto tol = 1.0e-3f;
 
     const auto all_floats = test_helpers::all_32_bit_floats (range.first, range.second, tol);
-    const auto y_exact = test_helpers::compute_all<float> (all_floats, FLOAT_FUNC (std::asinh));
+    const auto y_exact = test_helpers::compute_all<float> (all_floats, FLOAT_FUNC (std::expm1));
     // plot_ulp_error (all_floats, y_exact, FLOAT_FUNC ((math_approx::asinh<5>)), "asinh-5");
-    plot_ulp_error (all_floats, y_exact, FLOAT_FUNC ((math_approx::asinh<6>) ), "asinh-6");
-    plot_ulp_error (all_floats, y_exact, FLOAT_FUNC ((math_approx::asinh<7>) ), "asinh-7");
+    plot_error (all_floats, y_exact, FLOAT_FUNC ((math_approx::expm1<5>) ), "expm1-5");
+    plot_error (all_floats, y_exact, FLOAT_FUNC ((math_approx::expm1<6>) ), "expm1-6");
 
     plt::legend ({ { "loc", "upper right" } });
     plt::xlim (range.first, range.second);