From f783d7f274bf6fcbe3978a8414423cf1cb82ee04 Mon Sep 17 00:00:00 2001
From: Chip Hogg <chogg@aurora.tech>
Date: Sat, 8 Jan 2022 19:34:42 -0500
Subject: [PATCH] Handle `exp` explicitly in as_magnitude()

The new test actually passed without modifying the code.  However, that
might be implementation-dependent (presumably based on canonicalization
of the `ratio` template parameter), so I wanted a more obviously correct
implementation.
---
 src/core/include/units/magnitude.h        |  4 +++-
 test/unit_test/runtime/magnitude_test.cpp | 20 +++++++++++++++++++-
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/src/core/include/units/magnitude.h b/src/core/include/units/magnitude.h
index c4964337..bc333a43 100644
--- a/src/core/include/units/magnitude.h
+++ b/src/core/include/units/magnitude.h
@@ -333,7 +333,9 @@ constexpr auto operator/(Magnitude auto l, Magnitude auto r) { return l * pow<-1
 template<ratio R>
   requires (R.num > 0)
 constexpr Magnitude auto as_magnitude() {
-  return detail::prime_factorization_v<R.num> / detail::prime_factorization_v<R.den>;
+  return pow<R.exp>(detail::prime_factorization_v<10>)
+    * detail::prime_factorization_v<R.num>
+    / detail::prime_factorization_v<R.den>;
 }
 
 namespace detail
diff --git a/test/unit_test/runtime/magnitude_test.cpp b/test/unit_test/runtime/magnitude_test.cpp
index b32d2928..c0c8cb2e 100644
--- a/test/unit_test/runtime/magnitude_test.cpp
+++ b/test/unit_test/runtime/magnitude_test.cpp
@@ -86,13 +86,20 @@ TEST_CASE("base_power")
   SECTION("product with inverse equals identity")
   {
     auto check_product_with_inverse_is_identity = [] (auto x) {
-      CHECK(x * inverse(x) == as_magnitude<1>());
+      CHECK(x * pow<-1>(x) == as_magnitude<1>());
     };
 
     check_product_with_inverse_is_identity(as_magnitude<3>());
     check_product_with_inverse_is_identity(as_magnitude<ratio{4, 17}>());
     check_product_with_inverse_is_identity(pi_to_the<ratio{-22, 7}>());
   }
+
+  SECTION("pow() multiplies exponent")
+  {
+    CHECK(pow<0>(base_power{2}) == base_power{2, 0});
+    CHECK(pow<ratio{-1, 2}>(base_power{2, 3}) == base_power{2, ratio{-3, 2}});
+    CHECK(pow<ratio{1, 3}>(base_power<pi_base>{ratio{3, 2}}) == base_power<pi_base>{ratio{1, 2}});
+  }
 }
 
 TEST_CASE("make_ratio performs prime factorization correctly")
@@ -111,6 +118,13 @@ TEST_CASE("make_ratio performs prime factorization correctly")
   {
     CHECK(as_magnitude<ratio{5, 8}>() == magnitude<base_power{2, -3}, base_power{5}>{});
   }
+
+  SECTION("Supports nonzero exp")
+  {
+    constexpr ratio r{3, 1, 2};
+    REQUIRE(r.exp == 2);
+    CHECK(as_magnitude<r>() == as_magnitude<300>());
+  }
 }
 
 TEST_CASE("Equality works for magnitudes")
@@ -196,6 +210,10 @@ TEST_CASE("Can raise Magnitudes to rational powers")
     CHECK(pow<1>(as_magnitude<ratio{3, 4}>()) == as_magnitude<ratio{3, 4}>());
     CHECK(pow<1>(pi_to_the<ratio{-1, 2}>()) == pi_to_the<ratio{-1, 2}>());
   }
+
+  SECTION("Can raise to arbitrary rational power") {
+    CHECK(pow<ratio{-8, 3}>(pi_to_the<ratio{-1, 2}>()) == pi_to_the<ratio{4, 3}>());
+  }
 }
 
 namespace detail