From a62f061028d08a026a673ee8a42d1e80f5bda1ad Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Neboj=C5=A1a=20Cvetkovi=C4=87?= <nebkat@gmail.com>
Date: Sat, 20 Jan 2024 00:05:54 +0000
Subject: [PATCH] feat: `ppm` parts per million

Co-authored-by: Mateusz Pusz <mateusz.pusz@gmail.com>
---
 docs/users_guide/framework_basics/dimensionless_quantities.md | 2 ++
 src/core/include/mp-units/unit.h                              | 2 ++
 test/static/unit_symbol_test.cpp                              | 1 +
 3 files changed, 5 insertions(+)

diff --git a/docs/users_guide/framework_basics/dimensionless_quantities.md b/docs/users_guide/framework_basics/dimensionless_quantities.md
index 58949800..7215eb4e 100644
--- a/docs/users_guide/framework_basics/dimensionless_quantities.md
+++ b/docs/users_guide/framework_basics/dimensionless_quantities.md
@@ -160,6 +160,8 @@ with dimensionless quantities:
 ```cpp
 inline constexpr struct percent : named_unit<"%", mag<ratio{1, 100}> * one> {} percent;
 inline constexpr struct per_mille : named_unit<basic_symbol_text{"‰", "%o"}, mag<ratio(1, 1000)> * one> {} per_mille;
+inline constexpr struct parts_per_million : named_unit<"ppm", mag<ratio(1, 1'000'000)> * one> {} parts_per_million;
+inline constexpr auto ppm = parts_per_million;
 ```
 
 
diff --git a/src/core/include/mp-units/unit.h b/src/core/include/mp-units/unit.h
index cbcdde91..7c210cd2 100644
--- a/src/core/include/mp-units/unit.h
+++ b/src/core/include/mp-units/unit.h
@@ -605,6 +605,8 @@ template<std::intmax_t Num, std::intmax_t Den = 1, Unit U>
 // clang-format off
 inline constexpr struct percent : named_unit<"%", mag<ratio{1, 100}> * one> {} percent;
 inline constexpr struct per_mille : named_unit<basic_symbol_text{"‰", "%o"}, mag<ratio(1, 1000)> * one> {} per_mille;
+inline constexpr struct parts_per_million : named_unit<"ppm", mag<ratio(1, 1'000'000)> * one> {} parts_per_million;
+inline constexpr auto ppm = parts_per_million;
 // clang-format on
 
 
diff --git a/test/static/unit_symbol_test.cpp b/test/static/unit_symbol_test.cpp
index 24fe56fa..d52a2f8f 100644
--- a/test/static/unit_symbol_test.cpp
+++ b/test/static/unit_symbol_test.cpp
@@ -120,6 +120,7 @@ static_assert(unit_symbol(one) == "");
 static_assert(unit_symbol(percent) == "%");
 static_assert(unit_symbol(per_mille) == "‰");
 static_assert(unit_symbol<unit_symbol_formatting{.encoding = ascii}>(per_mille) == "%o");
+static_assert(unit_symbol(parts_per_million) == "ppm");
 static_assert(unit_symbol(square(metre)) == "m²");
 static_assert(unit_symbol<unit_symbol_formatting{.encoding = ascii}>(square(metre)) == "m^2");
 static_assert(unit_symbol(cubic(metre)) == "m³");