Fast-Float4HLS is a C++ header only library for floating point arithmetic operations developed to be used for High Level Synthesis implemetations.

Inside the header file <fast-float.h> is described a templated datatype ‘fast_float<M,E>’ together with a set of operations. The datatype supports different floating point representations depending on the definitions of the mantissa M and exponent E widths through the template. For example:

  • fast_float<23,8> is used for the single precision representation.
  • fast_float<52,11> is used for the double precision representation.
  • fast_float<7,8> is used for the representation of Brain Floating Point, bfloat16, developed by Google Brain.

Fast-Float4HLS is based on ac_int and ac_std_float libraries that are available in HLSLibs.

Supported Operators

  • Addition
  • Multiplication
  • Multiply-Add
  • Dot Product

Addition and multiplication are overloaded also to + and * operators. The same holds for comparisons and assignment operators


The operations of addition, multiplication and MAC support denormalized values through a template parameter ”DENORMALS”. By default, the operators do not support denormalized values, while converting them into zero values.

Currently the overloaded operators +, -, *, +=, -=, *= compute the corresponding operation without support for denormalized values.

Pending Features

  • Allow for possible increase the output precision of dot product.
  • support rounding on dot product
  • Implement Division


Currently active: Dionysios Filippas, Giorgos Dimitrakopoulos

Past: Nikolaos Altanis


Fast-Float4HLS is licensed with the MIT License. You are completely free to re-distribute your work derived from Fast-Float4HLS


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