computer science

Libfixmath

Libfixmath is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Libfixmath rather than just read about it. In short: libfixmath is a platform-independent fixed-point math library aimed at developers wanting to perform fast non-integer math on platforms lacking a (or with a low performance) FPU. It offers developers a similar interface to the standard math.h functions for use on Q16.16 fixed-point numbers. libfixmath has no external dependencies other than stdint.h and a compiler which supports 64-bit integer arithmetic (such as GC…

Key takeaways

Libfixmath belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Libfixmath to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Libfixmath from memory before moving on to harder problems.

Reference excerpt

libfixmath is a platform-independent fixed-point math library aimed at developers wanting to perform fast non-integer math on platforms lacking a (or with a low performance) FPU. It offers developers a similar interface to the standard math.h functions for use on Q16.16 fixed-point numbers. libfixmath has no external dependencies other than stdint.h and a compiler which supports 64-bit integer arithmetic (such as GCC). Conditional compilation options exist to remove the requirement for a 64-bit capable compiler as many compilers for microcontrollers and DSPs do not support 64-bit arithmetic.

History libfixmath was developed by Ben Brewer and first released publicly as part of the Dingoo SDK. It has since been used to implement a software 3D graphics library called FGL.

Q16.16 functions

Other functions

Performance For the most intensive function (atan2) benchmark results show the following results:

Note: These results were calculated using fixtest with caching optimizations turned off.

Licensing libfixmath is released under the MIT License, a permissive free software licence, and is free software.

Worked examples

Example 1 — a first encounter with Libfixmath

Start with the simplest possible case. Write down what Libfixmath claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Libfixmath before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Libfixmath ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Libfixmath

In research: Libfixmath appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Libfixmath in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Libfixmath is common in secondary-school and first-year university syllabi. It links to neighbouring topics C (programming language) libraries, Free computer libraries, Free software programmed in C, so understanding it makes those chapters shorter.
In everyday life: Look for Libfixmath outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Libfixmath in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Libfixmath means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Libfixmath out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Libfixmath in simple terms?

Why does Libfixmath matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Libfixmath?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Libfixmath.