From 89af9bebb9528d25c13850f22bf5bab119f8762b Mon Sep 17 00:00:00 2001
From: jatin <jatinchowdhury18@gmail.com>
Date: Sat, 23 Dec 2023 13:03:20 -0800
Subject: [PATCH] Add log1p and expm1

---
 README.md                              | 4 ++--
 include/math_approx/src/log_approx.hpp | 6 ++++++
 include/math_approx/src/pow_approx.hpp | 6 ++++++
 tools/plotter/plotter.cpp              | 8 ++++----
 4 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/README.md b/README.md
index 9878788..cb84580 100644
--- 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
index 11be37b..e778690 100644
--- 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
index b66b60b..a48efb6 100644
--- 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
index b1acf88..97b7820 100644
--- 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);