v3.3.0

Corrected Semantics for Ratio-Dimensionless Units

This release fixes multiple inconsistencies in the handling of ratio-dimensionless units
(e.g. percent, ppm, ppb) that previously could lead to silent precision loss, unit-scale loss,
or incorrect results in compound expressions.

These changes primarily affect arithmetic involving:

• integral-backed ratio-dimensionless units,
• compound units such as ppb / yr,
• accumulation over time or other dimensions.

---

1) Normalization and truncation behavior (fixed)

Previous behavior

Ratio-dimensionless units normalize to a fraction (e.g. 50% → 0.5), but that normalization could
happen in the unit’s underlying type. With integral underlying types, this could silently truncate.

Example:

percent<int>(50).value() == 0   // truncated from 0.5

This truncation could then propagate into arithmetic and comparisons.

Current behavior

Ratio-dimensionless units normalize in floating-point space when needed, so value() preserves the
fractional meaning regardless of underlying type:

percent<int>(50).value() == 0.5

---

2) Ratio scale could be lost in compound units (fixed)

Previous behavior

Expressions that form compound units from ratio-dimensionless numerators could discard the ratio
scale during type formation. For example, in:

ppb / yr

the result could behave as if it were effectively 1 / yr (dimensionally correct, numerically wrong).
This could surface when multiplying back by time:

(ppb_per_year * yr)  // could fail to round-trip to ppb semantics

Current behavior

Compound units preserve the ratio-dimensionless scale, so:

(ppb / yr) * yr  -> ppb

with the correct magnitude.

---

3) Mixed “points space” vs “fraction space” outcomes (fixed)

Ratio-dimensionless units have two relevant representations:

• raw(): the stored “points” (e.g. 50_pct.raw() == 50)
• value(): the normalized fraction (e.g. 50_pct.value() == 0.5)

Previous behavior

Semantically similar expressions could produce different results depending on which overloads were
selected (and thus whether raw() or value() was used internally).

Example class of issue:

dimensionless(1.0) / 50_pct    // not necessarily consistent with
1.0 / 50_pct

Current behavior

Scalar interactions with ratio-dimensionless units consistently use normalized values where a scalar
interpretation is intended, while unit-unit operations preserve ratio semantics until explicitly converted.

As a result, equivalent expressions remain equivalent in practice.

---

4) Compound assignment on ratio-dimensionless units is now defined

Previous behavior

Compound assignment operators (e.g. +=, *=, /=) could inherit the same inconsistencies described
above, especially for integral-backed ratio-dimensionless units.

Current behavior

Compound assignment behavior is explicitly defined so that:

• arithmetic is performed in the correct semantic domain (normalized when appropriate),
• the stored representation remains consistent and deterministic.

---

Summary of what changed for users

Before this release:

• Integral-backed ratio-dimensionless values could silently change meaning due to truncation.
• Compound unit formation could preserve dimensional correctness but lose numeric scale.
• Equivalent expressions could yield different results based on operand ordering and overload selection.

After this release:

• Ratio-dimensionless values are normalized consistently and without truncation.
• Ratio scale is preserved through compound unit arithmetic (e.g. rates like ppb/yr).
• Equivalent expressions are consistent in both type behavior and numeric results.

v3.2.0

Non-type template parameter (NTTP) support

v3.1.1

• update gtest to 1.17.0 (mostly to make CMake happy)
• update cmake support to 4.99
• better cmake exports
• add cpack for tar/deb/rpm

v2.3.5

• Fixes mil unit definition
• Adds jerk units to cmake/documentation

v3.1.0-beta

What's Changed

New Features:

• Uplift to C++23
• Alias template CTAD (meters length instead of meters<double> length)
• ADL Improvements
• SFINAE replaced by concepts where appropriate
• NAN support
• constexpr cmath functions
• Many new units (jerk, radiometric units, etc)
• unit constants (1.0 * km == kilometers(1.0))

Fixes:

• ternary operator works as expected
• cmake: Allow to use existing googletest package by @krf in #310
• Fix compile error under GCC-12 by @krf in #309
• MSVC-specific Empty Baseclass Optimization activation. by @Guillaume227 in #317
• Fix mil definition by @ts826848 in #321
• -Wshadow compilation warning fix - use -Wshadow for compiling tests by @Guillaume227 in #318
• introduce UNIT_NO_LITERAL_SUPPORT directive by @Guillaume227 in #316

New Contributors

• @krf made their first contribution in #310
• @Guillaume227 made their first contribution in #317

Full Changelog: v3.0.0.beta.2...v3.1.0-beta

v2.3.4

What's Changed

• Updated CMake policy version to resolve deprecation warning. by @joe-barnier in #337
• Added namePlural to UNIT_ADD_NAME by @raulcalvo in #338
• Some numeric_limits and numeric helper functions were missing by @siposcsaba89 in #331
• Add #undef PI by @codereptile in #336
• Avoid pascal macro conflict when working on mingw by @raghunandannm in #325
• Using intmax_t instead of size_t fixes narrowing conversion on 32bit by @pmaciol in #322
• Add jerk and RPS units by @AhmedAredah in #327
• Add inch_of_mercury by @adamdoda in #326

New Contributors

• @joe-barnier made their first contribution in #337
• @raulcalvo made their first contribution in #338
• @siposcsaba89 made their first contribution in #331
• @codereptile made their first contribution in #336
• @raghunandannm made their first contribution in #325
• @pmaciol made their first contribution in #322
• @AhmedAredah made their first contribution in #327
• @adamdoda made their first contribution in #326

Full Changelog: v2.3.3...v2.3.4

v3.0.0 Beta 2

What's Changed

• Fix incorrect math function output for scaled dimensionless types, v3.x edition by @ts826848 in #295
• fix locale unit test
• update gtest cmake
• add vs2019 to appveyor
• make .value() and .to<>() behave the same for scaled dimensionless units
• ensure consistency and testing of scaled dimensionless unit math functions

Full Changelog: v3.0.0.beta...v3.0.0.beta.2

v2.3.3

Fixes mil definition

v3.0.0 Beta

• added support for nlohmann json
• NaN support
• add Gal unit of acceleration
• improved stream operators

v2.3.2

Various fixes and improvements