fixmath

Fixmath is an experimental, header-only C++20 fixed-point arithmetic library. It provides configurable Q-format precision, arithmetic behavior, and rounding, with basic arithmetic for all supported types and math-function support currently focused on Q32.32 and Q16.16 values.

Project status: The API and test coverage are still evolving. Review behavior carefully before using the library in production or safety-critical code.

Features

• Selectable signed storage type and number of fractional bits.
• Ignore, strict, and saturating arithmetic modes.
• Round-to-zero and round-to-even policies.
• Integer, floating-point, and raw-representation conversions.
• Fixed-point arithmetic, comparisons, numeric limits, and square root support.
• Portable helpers for platforms without native 128-bit arithmetic.

Requirements

• A conforming C++20 compiler and standard library. Fixmath specifically depends on std::bit_cast, C++20 signed left-shift semantics, operator<=>, and concepts; see Required C++20 Features.
• CMake 3.10 or newer to build the tests.
• Network access during the first test configuration, because CMake fetches GoogleTest.

CI currently exercises Debug builds on Ubuntu and Windows.

Usage

Add include/ to your compiler's include path, then include the main header:

#include <fixmath/fixed.hpp>

using Q32_32 = fixmath::fixed<fixmath::fixed_policy<
    fixmath::int64_t,
    32,
    fixmath::arithmetic_mode::SaturationMode,
    fixmath::rounding_mode::RoundToEven>>;

int main() {
    const Q32_32 price{19.95};
    const Q32_32 quantity{3};
    const Q32_32 total = price * quantity;
    return total > Q32_32{0} ? 0 : 1;
}

Because the library is header-only, no separate library target needs to be linked.

Build and Test

From the repository root:

cmake -S tests -B build -DCMAKE_BUILD_TYPE=Debug
cmake --build build --config Debug
ctest --test-dir build -C Debug --output-on-failure

See AGENTS.md for repository layout, coding conventions, and contribution guidance.

Architecture and arithmetic details are collected in the documentation index.

AI-Assisted Development

This repository uses AI-assisted development. AI tools may help draft documentation, tests, and code changes. See the AI-Assisted Contributions guidelines for the review and validation requirements applied to generated work.

License

Fixmath is available under the Mozilla Public License 2.0.