v3.1.0

Added

• Precise integer time (opt-in utl/time_point.hpp): TimeDuration and
  TimeStamp, nanosecond-native int64 wrappers over Time<int64_t> with
  affine semantics — TimeStamp - TimeStamp yields a TimeDuration,
  TimeStamp +/- TimeDuration yields a TimeStamp, and TimeStamp + TimeStamp
  is deleted. to_time() bridges to the dimensional Time<double> (seconds).
  The floating-point unit machinery is untouched.
• std::chrono interop (opt-in utl/chrono.hpp): to_duration / to_timestamp
  convert from std::chrono::duration / time_point, and overloads of
  to_chrono convert TimeDuration / TimeStamp back. Kept separate so
  <chrono> is only included on demand.
• Readable dimension-mismatch diagnostics: adding, subtracting or comparing
  quantities of different dimensions now fails with a clear static_assert
  message (e.g. "utl: cannot add quantities of different dimensions") instead of
  an overload-resolution wall of "no matching operator" notes.
• Single-header amalgamation: single_include/utl/utl.hpp, generated from the
  multi-header tree by tools/amalgamate.py and kept in sync by CI, for
  zero-setup drop-in use. (The opt-in utl/io.hpp is not amalgamated.)
• Five more coherent derived units, each with a from-constituents constructor
  and an automatic result-type mapping: Vergence (1/m, diopter),
  Density (kg/m³), CurrentDensity (A/m²), Concentration (mol/m³) and
  Luminance (cd/m²). Luminance (cd/m²) is distinct from Illuminance
  (lm/m²) thanks to the angle dimension.

v3.0.0

Added

• Property-based tests (t_property) checking algebraic identities such as
  (a * b) / b == a and inv(inv(x)) == x across randomized values, as
  regression insurance for the mapper and operators.
• README status badges (CI, docs, latest release, license, C++17).
• Release automation: pushing a v* tag publishes a GitHub Release with notes
  drawn from the matching CHANGELOG.md section
  (tools/extract_changelog.sh, .github/workflows/release.yml).
• Zero-overhead proof (tools/check_zero_overhead.py, run in CI for gcc and
  clang): compiles unit arithmetic and the equivalent raw arithmetic to
  assembly at -O2 and asserts the two are byte-for-byte identical, making
  the zero-overhead claim a regression test.
• .clang-format codifying the house style, with a CI format job that fails
  on any unformatted file. clang-format is pinned so local and CI agree.
• Mixed-precision arithmetic: same-dimension +, -, the comparison operators
  and the cross-unit * / / now accept operands with different storage types
  (e.g. Length<float> + Length<double>) and promote the result to the wider
  type via std::common_type_t.
• TemperatureDelta type for affine-correct temperature arithmetic: a
  difference of temperatures is a displacement, not an absolute point, so its
  degC() / degF() apply only the scale factor and never the +273.15 /
  +32 offset. Supports Delta ± Delta, scalar * / /, unary -, and
  Temperature ± Delta.
• Packaging: a Conan recipe (conanfile.py with a test_package) and a vcpkg
  overlay port (packaging/vcpkg/ports), plus README install instructions for
  Conan, vcpkg and CMake FetchContent. The imported target is utl::utl
  everywhere.
• Angle as an eighth pseudo-dimension: Angle (rad) and SolidAngle (sr) are
  now distinct dimensions (rad = angle¹, sr = angle²), so Angle * Angle == SolidAngle, sqrt(SolidAngle) == Angle, and LuminousIntensity * SolidAngle == LuminousFlux. A new Torque (N·m = energy/angle) is type-distinct from
  Energy (Energy / Angle == Torque, Torque * Angle == Energy). Added
  sin / cos / tan overloads that take an Angle and return a scalar.

Changed (breaking)

• BaseUnit gained an eighth template exponent ANGLE (defaulted to 0, so
  named-unit code is unaffected) and dim() now returns std::array<int8_t, 8>.
  Angle and SolidAngle are no longer dimensionless — they carry the angle
  dimension — and LuminousFlux (cd·sr) is now type-distinct from
  LuminousIntensity (cd). Code reading dim() as a 7-element array, or
  relying on angles comparing equal to raw scalars, must adjust.

• ThermodynamicTemperature - ThermodynamicTemperature now returns a
  TemperatureDelta (was ThermodynamicTemperature), and
  ThermodynamicTemperature + ThermodynamicTemperature is deleted: adding two
  absolute temperatures is physically meaningless. Add a TemperatureDelta
  instead (temp + TemperatureDelta(5)). Reading a temperature difference
  via .degC() / .degF() previously misapplied the scale offset.

• BaseUnit default constructor is deleted: a physical quantity is never
  undefined. Every unit must be constructed with an explicit value. Callers
  that relied on default construction (e.g. std::map::operator[],
  value-initialized std::array) must initialize explicitly.

v2.0.0

Fixed

• Header-defined physical constants violated the ODR — any project
  including utl/utl.hpp from two translation units failed to link.
• virtual on BaseUnit::inv() added a vtable pointer to every unit
  (sizeof(Length<float>) was 16 instead of 4).
• Mass / Acceleration returned Force; the physically correct
  Mass * Acceleration is now derived from the dimension system.
• FAMTO prefix typo (now FEMTO), DAYS_IN_YEAR was 356,
  truncated km-to-mile factor replaced by the exact mile definition.
• M_PI (POSIX) replaced with portable utl::PI; the library now
  builds warning-free under MSVC /W4.

Changed (breaking)

• Cross-unit arithmetic is derived from dimension exponents via
  UnitMapper and requires #include <utl/utl.hpp>; single-unit
  headers no longer provide it. Hand-written per-class operators were
  removed (~800 lines).
• TimeTemperatureUnit renamed to TimeUnit, ElectricChangeUnit
  renamed to ElectricChargeUnit.
• type() on dimensionless results no longer yields Angle.
• Physical constants are constexpr (immutable) instead of mutable
  globals.

Added

• Whole library is constexpr; unit math evaluates at compile time.
• Unit literals: auto d = 120.0_km + 500.0_m;
• Comparison operators, compound assignment, unary minus.
• Stream output via utl/io.hpp: 30 [s^-1 m].
• Dimension-aware sqrt, pow<N>, abs, min, max.
• Imperial/engineering conversions: yd/ft/in, lb/oz, day,
  Wh/cal, hp, bar/atm/psi, mph.
• CMake utl::utl INTERFACE target with install/find_package
  support.
• CI on gcc, clang, MSVC and ASan/UBSan, with warnings as errors.
• mdBook user guide deployed to GitHub Pages.