Merge branch 'lut'

Author: danngreen

tests/lut_tests.cc

@@ -0,0 +1,40 @@
+#include "doctest.h"
+#include "util/lut.hh"
+
+struct VoltageToFreqTableRange {
+	static constexpr float min = -0.1f;
+	static constexpr float max = 0.5f;
+};
+constinit auto VoltageToFrequencyTable =
+	Mapping::LookupTable_t<50>::generate<VoltageToFreqTableRange>([](float x) { return x * x + 7; });
+
+TEST_CASE("check mapping table") {
+	constexpr unsigned LEN = 50;
+	constexpr float min = -0.1f;
+	constexpr float max = 0.5f;
+
+	// generate check data with original table:
+	// for (unsigned i = 0; i < LEN; i++) {
+	// 	auto x = min + i * (max - min) / float(LEN - 1);
+	// 	std::cout << "\t{" << x << ", " << VoltageToFrequencyTable.lookup(x) << "},\n";
+	// }
+	constexpr std::pair<float, float> checkdata[] = {
+		{-0.1, 7.01},		  {-0.0877551, 7.0077}, {-0.0755102, 7.0057}, {-0.0632653, 7.004}, {-0.0510204, 7.0026},
+		{-0.0387755, 7.0015}, {-0.0265306, 7.0007}, {-0.0142857, 7.0002}, {-0.00204081, 7},	   {0.0102041, 7.0001},
+		{0.022449, 7.0005},	  {0.0346939, 7.0012},	{0.0469388, 7.0022},  {0.0591837, 7.0035}, {0.0714286, 7.0051},
+		{0.0836735, 7.007},	  {0.0959184, 7.0092},	{0.108163, 7.0117},	  {0.120408, 7.0145},  {0.132653, 7.0176},
+		{0.144898, 7.021},	  {0.157143, 7.02469},	{0.169388, 7.02869},  {0.181633, 7.03299}, {0.193878, 7.03759},
+		{0.206122, 7.04249},  {0.218367, 7.04768},	{0.230612, 7.05318},  {0.242857, 7.05898}, {0.255102, 7.06508},
+		{0.267347, 7.07147},  {0.279592, 7.07817},	{0.291837, 7.08517},  {0.304082, 7.09247}, {0.316327, 7.10006},
+		{0.328571, 7.10796},  {0.340816, 7.11616},	{0.353061, 7.12465},  {0.365306, 7.13345}, {0.377551, 7.14254},
+		{0.389796, 7.15194},  {0.402041, 7.16164},	{0.414286, 7.17163},  {0.426531, 7.18193}, {0.438776, 7.19252},
+		{0.45102, 7.20342},	  {0.463265, 7.21461},	{0.47551, 7.22611},	  {0.487755, 7.23791}, {0.5, 7.25},
+	};
+
+	// Check data with refactored table:
+	for (unsigned i = 0; i < LEN; i++) {
+		auto x = min + i * (max - min) / float(LEN - 1);
+		auto y = VoltageToFrequencyTable.lookup(x);
+		CHECK(y == doctest::Approx(checkdata[i].second));
+	}
+}

util/lut.hh

@@ -0,0 +1,72 @@
+#pragma once
+#include <algorithm>
+#include <array>
+#include <cmath>
+#include <cstdint>
+
+namespace Mapping
+{
+
+namespace Impl
+{
+
+template<typename T, std::size_t LEN, typename rangeClass, typename F>
+struct EmptyArray {
+	constexpr EmptyArray(const F &func)
+		: data() {
+		constexpr float min = rangeClass::min;
+		constexpr float max = rangeClass::max;
+
+		for (std::size_t i = 0; i < LEN; i++) {
+			auto x = min + i * (max - min) / float(LEN - 1);
+			data[i] = func(x);
+		}
+	}
+	std::array<T, LEN> data;
+};
+
+} // namespace Impl
+
+template<std::size_t LEN>
+class LookupTable_t {
+public:
+	using Base_t = std::array<float, LEN>;
+
+public:
+	constexpr LookupTable_t(const float min_, const float max_, const Base_t &input)
+		: min(min_)
+		, max(max_) {
+		static_assert(LEN >= 2);
+		std::copy_n(input.begin(), LEN, points.begin());
+	}
+
+	constexpr float lookup(float val) const {
+		float idx = ((val - min) / (max - min)) * (LEN - 1);
+
+		if (idx <= 0.f)
+			return points.front();
+		else if (idx >= (LEN - 1))
+			return points.back();
+		else {
+			auto lower_idx = (uint32_t)idx;
+			float phase = idx - lower_idx;
+			auto lower = points[lower_idx];
+			auto upper = points[lower_idx + 1];
+			return lower + phase * (upper - lower);
+		}
+	}
+
+private:
+	Base_t points;
+	const float min;
+	const float max;
+
+public:
+	template<typename rangeClass, typename F>
+	static constexpr LookupTable_t generate(const F func) {
+		constexpr Impl::EmptyArray<float, LEN, rangeClass, F> dataArray(func);
+		return LookupTable_t(rangeClass::min, rangeClass::max, dataArray.data);
+	}
+};
+
+} // namespace Mapping