fastmath

This is a Modern Fortran library for fast, approximate math functions: exp, log, 1/sqrt.

These functions provide fast, approximate evaluations of the exponential, logarithm and normalization functions in 64-bit precision.

A detailed explanation of the underlying math with the IEEE-754 representation is reported in ref [1].

For each function, a module is provided; the interface has both simple functions and a programmable object-oriented wrapper.

References

This code is released under MIT license; please cite the following reference whenever using it.

[1] F. Perini, R.D. Reitz, "Fast approximations of exponential and logarithm functions combined with efficient storage/retrieval for combustion kinetics calculations" Combustion and Flame 194(2018), 37-51.

Building, using

An automated build is not available yet.

• src/fast_exp.f90 contains the exponential routines
• src/fast_log.f90 contains the logarithm routines
• src/fast_rsqrt.f90 contains the 1/sqrt(x) routines.
• test/test.f90 is the test driver program

Each module has no external dependencies, they can also be used individually.

A simple command line build script is:

gfortran src/fast_exp.f90 src/fast_log.f90 src/fast_rsqrt.f90 test/test.f90  -o fastmath_test.exe

A simple makefile for the GNU compiler suite is provided in folder project; to run it:

cd project/
make -f makefile.gcc

The testing executable compares performance and accuracy wrt the compiler's intrinsics functions.