Remove use of mp_units from //filter (#22)

Use of `mp_units` results in very long compile-times when building on
the Raspberry Pi. This commit removes its use from `//filter`.

Change-Id: I951300fa9db996dcc34544d780a6cf8e4f070119

filter/BUILD.bazel

@@ -4,5 +4,4 @@ cc_library(
     name = "filter",
     hdrs = ["filter.hpp"],
     visibility = ["//:__subpackages__"],
-    deps = ["@mp_units"],
 )

filter/filter.hpp

@@ -1,30 +1,22 @@
 #pragma once
 
-#include <mp-units/systems/si/si.h>
 #include <numbers>
+#include <utility>
 
 // Low and high pass filters
 // https://gitlab.com/mechmotum/row_filter/-/blob/master/row_filter/complementary.py
 
 namespace filter {
 
-namespace mp = mp_units;
-namespace si = mp_units::si;
-
-template <
-    auto CutoffFrequency,
-    auto SamplePeriod,
-    class Rep = double,
-    mp::Quantity Q = mp::quantity<mp::si::radian, Rep>>
+template <auto CutoffFrequency, auto SamplePeriod, class Rep = double>
 struct lowpass
 {
-  using rep_type = Rep;
+  using value_type = Rep;
 
-  static constexpr auto w0 = mp::quantity<si::radian / si::second, rep_type>{
-      2 * std::numbers::pi_v<rep_type> * CutoffFrequency};
-  static constexpr auto dt = mp::quantity<si::second, rep_type>{SamplePeriod};
+  static constexpr auto w0 =
+      2 * std::numbers::pi_v<value_type> * CutoffFrequency;
+  static constexpr auto dt = SamplePeriod;
 
-  using value_type = Q;
   using derivative_type = decltype(std::declval<value_type>() / dt);
 
   struct signal
@@ -41,20 +33,20 @@ struct lowpass
     static constexpr auto squared = [](auto x) { return x * x; };
 
     static constexpr auto a = squared(w0);
-    static constexpr auto b = std::numbers::sqrt2_v<rep_type> * w0;
+    static constexpr auto b = std::numbers::sqrt2_v<value_type> * w0;
 
     // Integrate the filter state equation using the midpoint Euler method with
     // time step h
     static constexpr auto h = dt;
     static constexpr auto h2 = squared(h);
-    static constexpr auto denom = 4 * mp::one + 2 * h * b + h2 * a;
+    static constexpr auto denom = 4 + 2 * h * b + h2 * a;
 
-    static constexpr auto A = (4 * mp::one + 2 * h * b - h2 * a) / denom;
+    static constexpr auto A = (4 + 2 * h * b - h2 * a) / denom;
     static constexpr auto B = 4 * h / denom;
     static constexpr auto C = -4 * h * a / denom;
-    static constexpr auto D = (4 * mp::one - 2 * h * b - h2 * a) / denom;
+    static constexpr auto D = (4 - 2 * h * b - h2 * a) / denom;
     static constexpr auto E = 2 * h2 * a / denom;
-    static constexpr auto F = 4 * mp::one * h * a / denom;
+    static constexpr auto F = 4 * h * a / denom;
 
     const auto x0 = value;
     const auto x1 = prev_unfiltered;
@@ -68,24 +60,16 @@ struct lowpass
   }
 };
 
-template <
-    auto CutoffFrequency,
-    auto SamplePeriod,
-    class Rep = double,
-    mp::Quantity Q = mp::quantity<mp::si::radian, Rep>>
+template <auto CutoffFrequency, auto SamplePeriod, class Rep = double>
 struct highpass
 {
-  using rep_type = Rep;
-
-  static constexpr auto w0 = mp::quantity<si::radian / si::second, rep_type>{
-      2 * std::numbers::pi_v<rep_type> * CutoffFrequency};
-  static constexpr auto dt = mp::quantity<si::second, rep_type>{SamplePeriod};
+  using value_type = Rep;
 
-  using value_type = Q;
+  static constexpr auto w0 =
+      2 * std::numbers::pi_v<value_type> * CutoffFrequency;
+  static constexpr auto dt = SamplePeriod;
 
-  using state_type = std::tuple<
-      mp::quantity<mp::si::second, rep_type>,
-      mp::quantity<mp::square(mp::si::second), rep_type>>;
+  using state_type = std::tuple<value_type, value_type>;
 
   value_type prev_unfiltered{};
   state_type prev_state{};
@@ -106,12 +90,12 @@ struct highpass
     const auto xim1 = prev_unfiltered;
     const auto [z1im1, z2im1] = prev_state;
 
-    static constexpr auto a0 = std::numbers::sqrt2_v<rep_type> * h * w0;
+    static constexpr auto a0 = std::numbers::sqrt2_v<value_type> * h * w0;
     static constexpr auto a1 = squared(h);
     static constexpr auto a2 = squared(w0);
     static constexpr auto a3 = a1 * a2;
     static constexpr auto a4 = 2 * a0;
-    static constexpr auto a5 = a3 + a4 + 4 * mp::one;
+    static constexpr auto a5 = a3 + a4 + 4;
     static constexpr auto a6 = 1 / a5;
     const auto a7 =
         a1 * xi + a1 * xim1 - a3 * z2im1 + a4 * z2im1 + 4 * h * z1im1 +
@@ -122,7 +106,7 @@ struct highpass
         a6 *
         (a5 * (-a0 * z1im1 - a8 * z2im1 + h * xi + h * xim1 + 2 * z1im1) -
          a7 * a8) /
-        (a0 + 2 * mp::one);
+        (a0 + 2);
     const auto z2i = a6 * a7;
     const auto yi = (z1i - z1im1) / h;
 

filter/test/filter_test.cpp

@@ -2,13 +2,24 @@
 
 #include <boost/ut.hpp>
 
-#include <mp-units/systems/si/si.h>
+// Clang does not yet support floating point NTTP
+//
+template <class T>
+struct constant
+{
+  using value_type = T;
+
+  // NOLINTNEXTLINE(cppcoreguidelines-avoid-const-or-ref-data-members)
+  const value_type value;
+
+  consteval constant(value_type val) : value{val} {}
 
-using namespace mp_units::si::unit_symbols;
+  constexpr operator T() const { return value; }
+};
 
 // NOLINTBEGIN(readability-magic-numbers)
-constexpr auto cutoff_freq = 20 * Hz;
-constexpr auto sample_period = 5 * ms;
+constexpr auto cutoff_freq = constant{20};       // Hz;
+constexpr auto sample_period = constant{0.005};  // ms;
 // NOLINTEND(readability-magic-numbers)
 
 auto main() -> int
@@ -18,13 +29,13 @@ auto main() -> int
 
   test("high pass filter invocable") = [] {
     auto highpass = filter::highpass<cutoff_freq, sample_period>{};
-    [[maybe_unused]] const auto [y0, z0] = highpass(1.0 * rad);
-    [[maybe_unused]] const auto _ = y0.number();
+    [[maybe_unused]] const auto [y0, z0] = highpass(1.0);
+    [[maybe_unused]] const auto _ = y0;
   };
 
   test("low pass filter invocable") = [] {
     auto lowpass = filter::lowpass<cutoff_freq, sample_period>{};
-    [[maybe_unused]] const auto [y0, yd0] = lowpass(1.0 * rad);
-    [[maybe_unused]] const auto _ = y0.number();
+    [[maybe_unused]] const auto [y0, yd0] = lowpass(1.0);
+    [[maybe_unused]] const auto _ = y0;
   };
 }