From 834d1fa09d2e93197ac5d9b053aa5fad999e36b7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Oliver=20Sch=C3=B6nrock?= <oliver@openbrackets.net>
Date: Thu, 20 Feb 2020 22:15:05 +0000
Subject: [PATCH] extending the range of operator* for incoherent units with
 large num/den this improves the situation for #55 (doesn't solve it outright)
 motivating examples which now work are: 1q_mi * 1q_mi * 1q_mi 1q_au * 1q_au
 tests added and docs updated

---
 doc/DESIGN.md                                |  2 +-
 src/include/units/bits/external/text_tools.h | 10 +++++-----
 src/include/units/concepts.h                 |  2 +-
 test/unit_test/runtime/fmt_units_test.cpp    |  6 ++++++
 4 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/doc/DESIGN.md b/doc/DESIGN.md
index 535c6740..b19bee64 100644
--- a/doc/DESIGN.md
+++ b/doc/DESIGN.md
@@ -78,7 +78,7 @@ where:
 
 ```cpp
 template<typename R>
-concept UnitRatio = Ratio<R> && (R::num * R::den > 0);
+concept UnitRatio = Ratio<R> && R::num > 0 && R::den > 0; // double negatives not allowed
 ```
 
 and `Ratio` is satisfied by any instantiation of `units::ratio<Num, Den, Exp>`.
diff --git a/src/include/units/bits/external/text_tools.h b/src/include/units/bits/external/text_tools.h
index aa6f9a03..aabf37a5 100644
--- a/src/include/units/bits/external/text_tools.h
+++ b/src/include/units/bits/external/text_tools.h
@@ -26,7 +26,7 @@
 
 namespace units::detail {
 
-template<int Value>
+template<std::intmax_t Value>
   requires (0 <= Value) && (Value < 10)
 inline constexpr basic_fixed_string superscript_number = "";
 
@@ -43,7 +43,7 @@ template<> inline constexpr basic_fixed_string superscript_number<9> = "\u2079";
 
 inline constexpr basic_fixed_string superscript_minus = "\u207b";
 
-template<int Value>
+template<std::intmax_t Value>
 constexpr auto superscript()
 {
   if constexpr(Value < 0)
@@ -54,12 +54,12 @@ constexpr auto superscript()
     return superscript<Value / 10>() + superscript<Value % 10>();
 }
 
-template<int Value>
+template<std::intmax_t Value>
 constexpr auto regular()
 {
-  if constexpr(Value < 0)
+  if constexpr (Value < 0)
     return basic_fixed_string("-") + superscript<-Value>();
-  else if constexpr(Value < 10)
+  else if constexpr (Value < 10)
     return basic_fixed_string(static_cast<char>('0' + Value));
   else
     return regular<Value / 10>() + regular<Value % 10>();
diff --git a/src/include/units/concepts.h b/src/include/units/concepts.h
index 11714e22..8bb3e666 100644
--- a/src/include/units/concepts.h
+++ b/src/include/units/concepts.h
@@ -79,7 +79,7 @@ concept Ratio = detail::is_ratio<T>;
 
 // UnitRatio
 template<typename R>
-concept UnitRatio = Ratio<R> && (R::num * R::den > 0);
+concept UnitRatio = Ratio<R> && R::num > 0 && R::den > 0; // double negatives not allowed
 
 // Unit
 template<UnitRatio R, typename U>
diff --git a/test/unit_test/runtime/fmt_units_test.cpp b/test/unit_test/runtime/fmt_units_test.cpp
index bf43b9f2..31291cef 100644
--- a/test/unit_test/runtime/fmt_units_test.cpp
+++ b/test/unit_test/runtime/fmt_units_test.cpp
@@ -175,4 +175,10 @@ TEST_CASE("fmt::format on synthesized unit symbols", "[text][fmt]")
   {
     CHECK(fmt::format("{}", 1q_in + 1q_yd) == "37 in");
   }
+
+  SECTION("incoherent units with powers")
+  {
+    CHECK(fmt::format("{}", 1q_mi * 1q_mi * 1q_mi) == "1 [15900351812136/3814697265625 × 10⁹] m³");
+    CHECK(fmt::format("{}", 1q_au * 1q_au) == "1 [2237952291797391849 × 10⁴] m²");
+  }
 }