CODEWITHSUNDEEP
c++cdata-structuresfloating-pointfixed-point
Shan
Shan

Reputation: 5232

data structures for floating point operation in fixed point processor

I need to program a fixed point processor that was used for a legacy application. New features are requested and these features need large dynamic range , most likely beyond the fixed point range even after scaling. As the processor will not be changed due to several reasons, I am planning to incorporate the floating point operation based on fixed point arithmetic-- basically software based approach. I want to define few data structures to represent a floating point numbers in C for the underlying fixed point processor. Is it possible to do at all? I am planning to use the IEEE floating point representation . What kind of data structures would be good for achieving basic operation like multiplication, division, add and sub . Are there already some open source libraries available in C /C++?

Upvotes: 2

Views: 582

Answers (2)

Lindydancer
Lindydancer

Reputation: 26094

Most C development tools for microcontrollers without native floating-point support provide software libraries for floating-point operations. Even if you do your programming in assembler, you could probably use those libraries. (Just curious, which processor and which development tools are you using?)

However, if you are serious about writing your own floating-point libraries, the most efficient way is to treat the routines as routines operating on integers. You can use unions, or code like to following to convert between floating-point and integer representation.

uint32_t integer_representation = *(uint32_t *)&fvalue;

Note that this is inherently undefined behavior, as the format of a floating-point number is not specified in the C standard.

The problem is much easier if you stick to floating-point and integer types that match (typically 32 or 64 bit types), that way you can see the routines as plain integer routines, as, for example, addition takes two 32 bit integer representations of floating-point values and return a 32 bit integer representation of the result.

Also, if you use the routines yourself, you could probably get away with leaving parts of the standard unimplemented, such as exception flags, subnormal numbers, NaN and Inf etc.

Upvotes: 1

Stephen Canon
Stephen Canon

Reputation: 106117

You don’t really need any data structures to do this. You simply use integers to represent floating-point encodings and integers to represent unpacked sign, exponent, and significand fields.

Upvotes: 0

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