Feat: Floor (#309)

* feat: first draft floor

* apply review feedback and move to desired files

* implement floor considering float types

* reduce code duplication

* apply review feedback and improve docstring

* enable static floor tests for gcc only

* Use recommended feature-test macro

* add floor runtime unittests

* apply review feedback

* make lambda const

src/core/include/units/math.h

@@ -147,4 +147,40 @@ template<Quantity Q>
   return Q(std::numeric_limits<typename Q::rep>::epsilon());
 }
 
+/**
+ * @brief Computes the largest quantity with integer representation and unit type To with its number not greater than q
+ *
+ * @tparam q Quantity being the base of the operation
+ * @return Quantity The rounded quantity with unit type To
+ */
+template<Unit To, typename D, typename U, typename Rep>
+[[nodiscard]] constexpr quantity<D, To, Rep> floor(const quantity<D, U, Rep>& q) noexcept
+  requires (!treat_as_floating_point<Rep>) ||
+    requires { floor(q.number()); } ||
+    requires { std::floor(q.number()); }
+{
+  const auto handle_signed_results = [&]<typename T>(const T& res) {
+    if (res > q)
+      return res - T::one();
+    return res;
+  };
+  if constexpr(treat_as_floating_point<Rep>) {
+    using std::floor;
+    if constexpr(std::is_same_v<To, U>) {
+      return quantity<D, To, Rep>(floor(q.number()));
+    }
+    else {
+      return handle_signed_results(quantity<D, To, Rep>(floor(quantity_cast<To>(q).number())));
+    }
+  }
+  else {
+    if constexpr(std::is_same_v<To, U>) {
+      return q;
+    }
+    else {
+      return handle_signed_results(quantity_cast<To>(q));
+    }
+  }
+}
+
 }  // namespace units

test/unit_test/runtime/math_test.cpp

@@ -24,10 +24,12 @@
 #include <units/isq/si/area.h>
 #include <units/isq/si/length.h>
 #include <units/isq/si/volume.h>
+#include <units/isq/si/time.h>
 #include <catch2/catch.hpp>
 #include <limits>
 
 using namespace units;
+using namespace units::isq;
 using namespace units::isq::si;
 
 // classical
@@ -108,6 +110,46 @@ TEST_CASE("numeric_limits functions", "[limits]")
   }
 }
 
+TEST_CASE("floor functions", "[floor]")
+{
+  SECTION ("floor 1 second with target unit second should be 1 second") {
+    REQUIRE(floor<si::second>(1_q_s) == 1_q_s);
+  }
+  SECTION ("floor 1000 milliseconds with target unit second should be 1 second") {
+    REQUIRE(floor<si::second>(1000_q_ms) == 1_q_s);
+  }
+  SECTION ("floor 1001 milliseconds with target unit second should be 1 second") {
+    REQUIRE(floor<si::second>(1001_q_ms) == 1_q_s);
+  }
+  SECTION ("floor 1999 milliseconds with target unit second should be 1 second") {
+    REQUIRE(floor<si::second>(1999_q_ms) == 1_q_s);
+  }
+  SECTION ("floor -1000 milliseconds with target unit second should be -1 second") {
+    REQUIRE(floor<si::second>(-1000_q_ms) == -1_q_s);
+  }
+  SECTION ("floor -999 milliseconds with target unit second should be -1 second") {
+    REQUIRE(floor<si::second>(-999_q_ms) == -1_q_s);
+  }
+  SECTION ("floor 1.3 seconds with target unit second should be 1 second") {
+    REQUIRE(floor<si::second>(1.3_q_s) == 1_q_s);
+  }
+  SECTION ("floor -1.3 seconds with target unit second should be -1 second") {
+    REQUIRE(floor<si::second>(-1.3_q_s) == -2_q_s);
+  }
+  SECTION ("floor 1001. milliseconds with target unit second should be 1 second") {
+    REQUIRE(floor<si::second>(1001._q_ms) == 1_q_s);
+  }
+  SECTION ("floor 1999. milliseconds with target unit second should be 1 second") {
+    REQUIRE(floor<si::second>(1999._q_ms) == 1_q_s);
+  }
+  SECTION ("floor -1000. milliseconds with target unit second should be -1 second") {
+    REQUIRE(floor<si::second>(-1000._q_ms) == -1_q_s);
+  }
+  SECTION ("floor -999. milliseconds with target unit second should be -1 second") {
+    REQUIRE(floor<si::second>(-999._q_ms) == -1_q_s);
+  }
+}
+
 TEMPLATE_TEST_CASE_SIG("pow<N>() implementation exponentiates values to power N", "[math][pow][exp]",
                        (std::intmax_t N, N), 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25)
 {

test/unit_test/static/math_test.cpp

@@ -25,6 +25,7 @@
 #include <units/isq/si/length.h>
 #include <units/isq/si/area.h>
 #include <units/isq/si/volume.h>
+#include <units/isq/si/time.h>
 #include <units/isq/si/international/length.h>
 #include <units/isq/si/international/area.h>
 #include <units/isq/si/international/volume.h>
@@ -32,6 +33,7 @@
 namespace {
 
 using namespace units;
+using namespace units::isq;
 using namespace units::isq::si::literals;
 using namespace units::isq::si::international::literals;
 
@@ -55,4 +57,26 @@ static_assert(compare<decltype(pow<1, 4>(4_q_m2)), decltype(sqrt(2_q_m))>);
 static_assert(compare<decltype(pow<1, 4>(4_q_km2)), decltype(sqrt(2_q_km))>);
 static_assert(compare<decltype(pow<1, 4>(4_q_ft2)), decltype(sqrt(2_q_ft))>);
 
+#if __cpp_lib_constexpr_cmath  // TODO remove once std::floor is constexpr for all compilers
+// floor
+// integral types
+static_assert(compare<decltype(floor<si::second>(1_q_s)), decltype(1_q_s)>);
+
+static_assert(compare<decltype(floor<si::second>(1000_q_ms)), decltype(1_q_s)>);
+static_assert(compare<decltype(floor<si::second>(1001_q_ms)), decltype(1_q_s)>);
+static_assert(compare<decltype(floor<si::second>(1999_q_ms)), decltype(1_q_s)>);
+static_assert(compare<decltype(floor<si::second>(-1000_q_ms)), decltype(-1_q_s)>);
+static_assert(compare<decltype(floor<si::second>(-999_q_ms)), decltype(-1_q_s)>);
+
+// floating-point
+static_assert(floor<si::second>(1.3_q_s) == 1_q_s);
+static_assert(floor<si::second>(-1.3_q_s) == -2_q_s);
+
+// static_assert(floor<si::second>(1000._q_ms) == 1_q_s);  // does not work due to a bug in fpow10() see #311
+static_assert(floor<si::second>(1001._q_ms) == 1_q_s);
+static_assert(floor<si::second>(1999._q_ms) == 1_q_s);
+static_assert(floor<si::second>(-1000._q_ms) == -1_q_s);
+static_assert(floor<si::second>(-999._q_ms) == -1_q_s);
+#endif
+
 }  // namespace