Reorder the string generation (#303)

* Reorder the string generation to prioritize base units when generating strings

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

config/cppcheck_suppressions.txt

@@ -1,6 +1,6 @@
 unusedFunction:units/x12_conv.cpp:1024
 unusedFunction:units/r20_conv.cpp:2738
 unusedFunction:units/x12_conv.cpp:1009
-passedByValue:units/units.cpp:215
-passedByValue:units/units.cpp:1147
-passedByValue:units/units.cpp:1164
+passedByValue:units/units.cpp:222
+passedByValue:units/units.cpp:1154
+passedByValue:units/units.cpp:1171

test/test_unit_strings.cpp

@@ -60,7 +60,7 @@ TEST(unitStrings, squared)
 
 TEST(unitStrings, Combos)
 {
- EXPECT_EQ(to_string(V / km), "V/km");
+ EXPECT_EQ(to_string(V / km), "mV/m");
  EXPECT_EQ(to_string(currency / MWh), "$/MWh");
  EXPECT_EQ(to_string(currency / mile), "$/mi");
  EXPECT_EQ(to_string(kW / gal), "kW/gal");
@@ -416,6 +416,14 @@ TEST(unitStrings, Hertz)
  EXPECT_EQ(to_string(precise::tera * precise::Hz), "THz");
 }
 
+TEST(unitStrings, singleBase)
+{
+ EXPECT_EQ(to_string(precise::kilo * precise::J / precise::mol), "kJ/mol");
+ EXPECT_EQ(
+ to_string(precise::kilo * precise::J / precise::rad.pow(2)),
+ "kJ/rad^2");
+}
+
 TEST(unitStrings, watthours)
 {
  EXPECT_EQ(to_string(precise::A * precise::s), "C");
@@ -1143,7 +1151,9 @@ TEST(userDefinedUnits, definitions)
 
  EXPECT_EQ(to_string(clucks * V), "clucks*V");
 
- EXPECT_EQ(to_string(clucks * mol), "mol*clucks");
+ EXPECT_EQ(to_string(clucks * mol), "clucks*mol");
+
+ EXPECT_EQ(to_string(clucks * hp), "hp*clucks");
 
  EXPECT_EQ(to_string(clucks.pow(2) * kg), "kg*clucks^2");
 

units/units.cpp

@@ -164,9 +164,17 @@ static const umap base_unit_names = getDefinedBaseUnitNames();
 
 using ustr = std::pair<precise_unit, const char*>;
 // units to divide into tests to explore common multiplier units
-static UNITS_CPP14_CONSTEXPR_OBJECT std::array<ustr, 23> testUnits{
+static UNITS_CPP14_CONSTEXPR_OBJECT std::array<ustr, 29> testUnits{
  {ustr{precise::m, "m"},
  ustr{precise::s, "s"},
+ ustr{precise::kg, "kg"},
+ ustr{precise::mol, "mol"},
+ ustr{precise::currency, "$"},
+ ustr{precise::rad, "rad"},
+ ustr{precise::count, "item"},
+ ustr{precise::candela, "cd"},
+ ustr{precise::Ampere, "A"},
+ ustr{precise::Kelvin, "K"},
  ustr{precise::ms, "ms"},
  ustr{precise::min, "min"},
  ustr{precise::hr, "hr"},
@@ -177,9 +185,7 @@ static UNITS_CPP14_CONSTEXPR_OBJECT std::array<ustr, 23> testUnits{
  ustr{constants::c.as_unit(), "[c]"},
  ustr{constants::h.as_unit(), "[h]"},
  ustr{precise::L, "L"},
- ustr{precise::kg, "kg"},
  ustr{precise::km, "km"},
- ustr{precise::currency, "$"},
  ustr{precise::volt, "V"},
  ustr{precise::watt, "W"},
  ustr{precise::electrical::kW, "kW"},
@@ -191,10 +197,11 @@ static UNITS_CPP14_CONSTEXPR_OBJECT std::array<ustr, 23> testUnits{
 
 // units to divide into tests to explore common multiplier units which can be
 // multiplied by power
-static UNITS_CPP14_CONSTEXPR_OBJECT std::array<ustr, 5> testPowerUnits{
+static UNITS_CPP14_CONSTEXPR_OBJECT std::array<ustr, 6> testPowerUnits{
  {ustr{precise::m, "m"},
- ustr{precise::km, "km"},
  ustr{precise::s, "s"},
+ ustr{precise::radian, "rad"},
+ ustr{precise::km, "km"},
  ustr{precise::ft, "ft"},
  ustr{precise::mile, "mi"}}};
 
@@ -1567,11 +1574,22 @@ static std::string
  return std::string("1/") + prefix;
  }
 
- // let's try common units
+ // let's try common unit combinations
+ std::string beststr;
+
  for (const auto& tu : testUnits) {
- auto res = probeUnit(un, tu);
- if (!res.empty()) {
- return res;
+ auto str = probeUnit(un, tu);
+ if (!str.empty()) {
+ return str;
+ }
+ str = probeUnitBase(un, tu);
+ if (!str.empty()) {
+ if (!isNumericalStartCharacter(str.front())) {
+ return str;
+ }
+ if (beststr.empty() || str.size() < beststr.size()) {
+ beststr = str;
+ }
  }
  }
 
@@ -1617,19 +1635,7 @@ static std::string
  return res;
  }
  }
- std::string beststr;
 
- for (const auto& tu : testUnits) {
- auto str = probeUnitBase(un, tu);
- if (!str.empty()) {
- if (!isNumericalStartCharacter(str.front())) {
- return str;
- }
- if (beststr.empty() || str.size() < beststr.size()) {
- beststr = str;
- }
- }
- }
  if (allowUserDefinedUnits.load(std::memory_order_acquire)) {
  for (const auto& udu : user_defined_unit_names) {
  auto str = probeUnitBase(