Add power function

CMakeLists.txt

@@ -73,6 +73,7 @@ if(NOT CMAKE_CROSSCOMPILING)
             "lib/grit/fft/fft_test.cpp"
             "lib/grit/math/ilog2_test.cpp"
             "lib/grit/math/ipow_test.cpp"
+            "lib/grit/math/power_test.cpp"
             "lib/grit/math/normalizable_range_test.cpp"
             "lib/grit/math/static_lookup_table_test.cpp"
             "lib/grit/unit/decibel_test.cpp"

lib/CMakeLists.txt

@@ -71,7 +71,9 @@ target_sources(gritwave-grit INTERFACE
         "grit/math/ilog2.hpp"
         "grit/math/ipow.hpp"
         "grit/math/linear_interpolation.hpp"
+        "grit/math/normalizable_range.hpp"
         "grit/math/remap.hpp"
+        "grit/math/power.hpp"
         "grit/math/sign.hpp"
         "grit/math/static_lookup_table.hpp"
         "grit/math/static_lookup_table_transform.hpp"

lib/grit/math.hpp

@@ -8,6 +8,7 @@
 #include <grit/math/ipow.hpp>
 #include <grit/math/linear_interpolation.hpp>
 #include <grit/math/normalizable_range.hpp>
+#include <grit/math/power.hpp>
 #include <grit/math/remap.hpp>
 #include <grit/math/sign.hpp>
 #include <grit/math/static_lookup_table.hpp>

lib/grit/math/power.hpp

@@ -0,0 +1,44 @@
+#pragma once
+
+#include <etl/concepts.hpp>
+
+namespace grit {
+
+/// \ingroup grit-math
+template<int Exponent, typename Numeric>
+    requires(Exponent >= 0)
+[[nodiscard]] constexpr auto power(Numeric base) -> Numeric
+{
+    // Unrolling is necessary when not compiling with `-ffast-math`.
+    // https://godbolt.org/z/bEnvWKdsq
+
+    if constexpr (Exponent == 0) {
+        return Numeric(1);
+    } else if constexpr (Exponent == 1) {
+        return base;
+    } else if constexpr (Exponent == 2) {
+        return base * base;
+    } else if constexpr (Exponent == 3) {
+        return base * power<2>(base);
+    } else if constexpr (Exponent == 4) {
+        auto const x2 = power<2>(base);
+        return x2 * x2;
+    } else if constexpr (Exponent == 5) {
+        return base * power<4>(base);
+    } else if constexpr (Exponent == 6) {
+        return power<2>(base) * power<4>(base);
+    } else if constexpr (Exponent == 7) {
+        auto const x2 = power<2>(base);
+        auto const x4 = x2 * x2;
+        return base * x2 * x4;
+    } else if constexpr (Exponent == 8) {
+        auto const x2 = power<2>(base);
+        auto const x3 = x2 * base;
+        auto const x6 = x3 * x3;
+        return x6 * x2;
+    } else {
+        return base * power<Exponent - 1>(base);
+    }
+}
+
+}  // namespace grit

lib/grit/math/power_test.cpp

@@ -0,0 +1,49 @@
+#include "power.hpp"
+
+#include <catch2/catch_template_test_macros.hpp>
+#include <catch2/matchers/catch_matchers_floating_point.hpp>
+
+TEMPLATE_TEST_CASE(
+    "grit/math: power",
+    "",
+    short,
+    int,
+    long,
+    long long,
+    unsigned short,
+    unsigned int,
+    unsigned long,
+    unsigned long long
+)
+{
+    using Int = TestType;
+
+    REQUIRE(grit::power<1>(Int(1)) == 1);
+    REQUIRE(grit::power<1>(Int(2)) == 2);
+    REQUIRE(grit::power<1>(Int(3)) == 3);
+
+    REQUIRE(grit::power<2>(Int(1)) == 1);
+    REQUIRE(grit::power<2>(Int(2)) == 4);
+    REQUIRE(grit::power<2>(Int(3)) == 9);
+
+    REQUIRE(grit::power<3>(Int(1)) == 1);
+    REQUIRE(grit::power<3>(Int(2)) == 8);
+    REQUIRE(grit::power<3>(Int(3)) == 27);
+}
+
+TEMPLATE_TEST_CASE("grit/math: power", "", float, double)
+{
+    using Float = TestType;
+
+    REQUIRE_THAT(grit::power<1>(Float(1)), Catch::Matchers::WithinAbs(1, 1e-8));
+    REQUIRE_THAT(grit::power<1>(Float(2)), Catch::Matchers::WithinAbs(2, 1e-8));
+    REQUIRE_THAT(grit::power<1>(Float(3)), Catch::Matchers::WithinAbs(3, 1e-8));
+
+    REQUIRE_THAT(grit::power<2>(Float(1)), Catch::Matchers::WithinAbs(1, 1e-8));
+    REQUIRE_THAT(grit::power<2>(Float(2)), Catch::Matchers::WithinAbs(4, 1e-8));
+    REQUIRE_THAT(grit::power<2>(Float(3)), Catch::Matchers::WithinAbs(9, 1e-8));
+
+    REQUIRE_THAT(grit::power<3>(Float(1)), Catch::Matchers::WithinAbs(1, 1e-8));
+    REQUIRE_THAT(grit::power<3>(Float(2)), Catch::Matchers::WithinAbs(8, 1e-8));
+    REQUIRE_THAT(grit::power<3>(Float(3)), Catch::Matchers::WithinAbs(27, 1e-8));
+}