math module

README.md

@@ -1,6 +1,8 @@
-Modules:
+## Modules:
 - `util`: General purpose math functions, interpolation, array handling, etc.
 
+## Including modules in your project:
+
 Set variable `$(RUSEFI_LIB)` to the path to the folder that contains this readme.
 
 Include the mk files of the modules that you want, then add:
@@ -8,3 +10,7 @@ Include the mk files of the modules that you want, then add:
 - `$(RUSEFI_LIB_CPP)` to your list of c++ input files
 
 Currently, C++17 is required to compile these libraries.
+
+## Unit tests:
+
+TODO

util/include/rusefi/math.h

@@ -0,0 +1,27 @@
+// Various math utility functions, implemented in microcontroller friendly ways.
+
+#pragma once
+
+// absolute value
+int absI(int value);
+float absF(float value);
+
+// Min/max
+int maxI(int i1, int i2);
+int minI(int i1, int i2);
+float maxF(float i1, float i2);
+float minF(float i1, float i2);
+
+// Clamping
+float clampF(float min, float clamp, float max);
+
+// Returns if two floats are within 0.0001
+bool isSameF(float a, float b);
+
+// @brief Compute e^x using a 4th order taylor expansion centered at x=-1.  Provides
+// bogus results outside the range -2 < x < 0.
+float expf_taylor(float x);
+
+// @brief Compute tan(theta) using a ratio of the Taylor series for sin and cos
+// Valid for the range [0, pi/2 - 0.01]
+float tanf_taylor(float theta);

util/src/math.cpp

@@ -0,0 +1,95 @@
+#include <rusefi/math.h>
+
+#include <cstdint>
+
+float absF(float value) {
+	return value > 0 ? value : -value;
+}
+
+int absI(int value) {
+	return value >= 0 ? value : -value;
+}
+
+int maxI(int i1, int i2) {
+	return i1 > i2 ? i1 : i2;
+}
+
+int minI(int i1, int i2) {
+	return i1 < i2 ? i1 : i2;
+}
+
+float maxF(float i1, float i2) {
+	return i1 > i2 ? i1 : i2;
+}
+
+float minF(float i1, float i2) {
+	return i1 < i2 ? i1 : i2;
+}
+
+float clampF(float min, float clamp, float max) {
+	return maxF(min, minF(clamp, max));
+}
+
+bool isSameF(float a, float b) {
+	return absF(a - b) < 0.0001;
+}
+
+constexpr float expf_taylor_impl(float x, uint8_t n)
+{
+	if (x < -2)
+	{
+		return 0.818f;
+	}
+	else if (x > 0)
+	{
+		return 1;
+	}
+
+	x = x + 1;
+
+	float x_power = x;
+	int fac = 1;
+	float sum = 1;
+
+	for (int i = 1; i <= n; i++)
+	{
+		fac *= i;
+		sum += x_power / fac;
+
+		x_power *= x;
+	}
+
+	constexpr const float constant_e = 2.71828f;
+	return sum / constant_e;
+}
+
+float expf_taylor(float x)
+{
+	return expf_taylor_impl(x, 4);
+}
+
+float tanf_taylor(float x) {
+	// This exists because the "normal" implementation, tanf, pulls in like 6kb of
+	// code and loookup tables
+
+	// This is only specified from [0, pi/2 - 0.01)
+	// Inside that range it has an error of less than 0.1%, and it gets worse as theta -> pi/2
+
+	// Precompute some exponents of x
+	float x2 = x * x;
+	float x3 = x2 * x;
+	float x4 = x3 * x;
+	float x5 = x4 * x;
+	float x6 = x5 * x;
+	// x7 not used
+	float x8 = x6 * x2;
+
+	// 3-term Taylor Series for sin(theta)
+	float sin_val = x - (x3 / 6) + (x5 / 120);
+
+	// 5-term Taylor Series for cos(theta)
+	float cos_val = 1 - (x2 / 2) + (x4 / 24) - (x6 / 720) + (x8 / 40320);
+
+	// tan = sin / cos
+	return sin_val / cos_val;
+}

util/test/test_math.cpp

@@ -0,0 +1,39 @@
+#include <rusefi/math.h>
+
+#include <gtest/gtest.h>
+#include <math.h>
+
+TEST(Util_Math, ExpTaylor)
+{
+    float x = -2;
+
+    // test from -2 < x < 0
+    for(float x = -2; x < 0; x += 0.05)
+    {
+        // Compare taylor to libc implementation
+        EXPECT_NEAR(expf_taylor(x), expf(x), 0.01f);
+    }
+}
+
+TEST(Util_Math, clampf) {
+	// off scale low
+	EXPECT_EQ(clampF(10, 5, 20), 10);
+	EXPECT_EQ(clampF(-10, -50, 10), -10);
+
+	// in range (unclamped)
+	EXPECT_EQ(clampF(10, 15, 20), 15);
+	EXPECT_EQ(clampF(-10, -5, 10), -5);
+
+	// off scale high
+	EXPECT_EQ(clampF(10, 25, 20), 20);
+	EXPECT_EQ(clampF(-10, 50, 10), 10);
+}
+
+TEST(Util_Math, tanf_taylor) {
+	// Function is only specified from [0, pi/2) ish, so test that range
+	for (float i = 0; i < 1.5; i += 0.1f)
+	{
+		// Compare to libc implementation
+		EXPECT_NEAR(tanf_taylor(i), tanf(i), 0.05f) << "I = " << i;
+	}
+}

util/util.mk

@@ -3,4 +3,8 @@ RUSEFI_LIB_INC += $(RUSEFI_LIB)/util/include
 RUSEFI_LIB_CPP += \
 	$(RUSEFI_LIB)/util/src/util_dummy.cpp \
 	$(RUSEFI_LIB)/util/src/crc.cpp \
+	$(RUSEFI_LIB)/util/src/math.cpp \
+
+RUSEFI_LIB_CPP_TEST += \
+	$(RUSEFI_LIB)/util/test/test_math.cpp \