SLEEF libm has three kinds of testers, and each kind of testers has its own role.
The first kind of testers consists of a tester and an IUT (which stands for Implementation Under Test.) The role for this tester is to perform a perfunctory set of tests to check if the build is correct. In this test, the functions in the library are tested if the evaluation error is within the designed limit by comparing the returned values against high-precision evaluation using the GNU MPFR Library. The tester and IUT are built as separate executables, and communicate with each other using a pipe. Since these two are separate, the IUT can be implemented with an exotic languages or on an operating system that does not support libraries required for testing. It is also possible to perform a test over the network.
The second kind of testers are designed to run continuously. It repeats randomly generating arguments for each function, and comparing the results of each function to the results calculated with the corresponding function in the MPFR library. This tester is expected to find bugs if it is run for sufficiently long time. In these tests, we especially carefully check the error of the trigonometric functions with arguments close to an integral multiple of π/2.
The third kind of testers are for testing if bit-identical results are returned from the functions that are supposed to return such results. The MD5 hash value of all returned values from each function is calculated and checked if it matches the precomputed value.
SLEEF DFT has three kinds of testers. The first ones, named naivetest, compare the results computed by SLEEF DFT with those by a naive DFT implementation. These testers cannot be built with MSVC since complex data types are not supported. The second testers, named fftwtest, compare the results of computation between SLEEF DFT and FFTW. This test requires FFTW library. The third testers, named roundtriptest, executes a forward transform followed by a backward transform. Then, it compares the results with the original data. While this test does not require external library and it runs on all environment, there could be cases where this test does not find some flaw. The roundtrip testers are used only if FFTW is not available.
Gencoef is a small tool for generating the coefficients for polynomial approximation used in the kernels.
In order to change the configurations, please edit gencoefdp.c. In the beginning of the file, specifications of the parameters for generating coefficients are listed. Please enable one of them by changing #if. Then, run make to compile the source code. Run the gencoef, and it will show the generated coefficients in a few minutes. It may take longer time depending on the settings.
There are two phases of the program. The first phase is the regression for minimizing the maximum relative error. This problem can be reduced to a linear programming problem, and the Simplex method is used in this implementation. This requires multi-precision calculation, and the implementation uses the MPFR library. In this phase, it uses only a small number of values (specified by the macro S, usually less than 100) within the input domain of the kernel function to approximate the function. The function to approximate is given by FRFUNC function. Specifying higher values for S does not always give better results.
The second phase is to optimize the coefficients so that it gives good accuracy with double precision calculation. In this phase, it checks 10000 points (specified by the macro Q) within the specified argument range to see if the polynomial gives good error bounds. In some cases, the last few terms have to be calculated in higher precision in order to achieve 1 ULP or better overall accuracy, and this implementation can take care of that. The L parameter specifies the number of high precision coefficients.
In some cases, it is desirable to fix the last few coefficients to values like 1 or 0.5. This can be specified if you define FIXCOEF0 macro.
Finding a set of good parameters is not a straightforward process.
SLEEF has a tool for measuring and plotting execution time of each function in the library. It consists of an executable for measurements, a makefile for driving measurement and plotting, and a couple of scripts.
In order to start a measurement, you need to first build the executable for measurement. CMake builds the executable along with the library. Please refer to compiling and installing the library for this.
Then, change directory to sleef-3.X/src/libm-benchmarks/. You also need to set the build directory to BUILDDIR environment variable. You also need Java runtime environment.
$ export BUILDDIR=$PATH:`pwd`/../../build
Type "make measure". After compiling the tools, it will prompt a label for measurement. After you input a label, measurement begins. After a measurement finishes, you can repeat measurements under different configurations. If you want to measure on a different computer, please copy the entire directory on to that computer and continue measurements. If you have Intel Compiler installed on your computer, you can type "make measureSVML" to measure the computation time of SVML functions.
$ make measure
./measure.sh benchsleef
...
Enter label of measurement(e.g. My desktop PC) : Skylake
Measurement in progress. This may take several minutes.
Sleef_sind2_u10
Sleef_cosd2_u10
Sleef_tand2_u10
Sleef_sincosd2_u10
...
Sleef_atanf8_u10
Sleef_atan2f8_u10
Sleef_atanf8_u35
Sleef_atan2f8_u35
Now, you can plot the results of measurement by 'make plot'.
You can do another measurement by 'make measure'.
You can start over by 'make restart'.
$ make plot
javac ProcessData.java
java ProcessData *dptrig*.out
gnuplot script.out
mv output.png trigdp.png
java ProcessData *dpnontrig*.out
gnuplot script.out
mv output.png nontrigdp.png
java ProcessData *sptrig*.out
gnuplot script.out
mv output.png trigsp.png
java ProcessData *spnontrig*.out
gnuplot script.out
mv output.png nontrigsp.png
$ █
Then type "make plot" to generate graphs. You need to have JDK and gnuplot installed on your computer. Four graphs are generated : trigdp.png, nontrigdp.png, trigsp.png and nontrigsp.png. Please see our benchmark results for an example of generated graphs by this tool.