GCE-Math (Generalized Constant Expression Math) is a templated C++ library enabling compile-time computation of mathematical functions.
Features:
- The library is written in C++11
constexpr
format, and is C++11/14/17 compatible. - Continued fraction and series expansions are implemented using recursive templates.
- The
gcem::
syntax is identical to the C++ standard library (std::
). - Tested and accurate to floating-point precision against the C++ standard library.
- Released under a permissive, non-GPL license.
Author: Keith O'Hara
The library is actively maintained, and is still being extended. A list of features includes:
- basic library functions:
abs
,exp
,log
,max
,min
,pow
,sqrt
,gcd
,lcm
, and more
- trigonometric functions:
- basic:
cos
,sin
,tan
- inverse:
acos
,asin
,atan
,atan2
- basic:
- hyperbolic (area) functions:
cosh
,sinh
,tanh
,acosh
,asinh
,atanh
- special functions:
- factorials and the binomial coefficient:
factorial
,binomial_coef
- beta, gamma, and multivariate gamma functions:
beta
,lbeta
,lgamma
,tgamma
,lmgamma
- the Gaussian error function and inverse error function:
erf
,erf_inv
- (regularized) incomplete beta and incomplete gamma functions:
incomplete_beta
,incomplete_gamma
- inverse incomplete beta and incomplete gamma functions:
incomplete_beta_inv
,incomplete_gamma_inv
- factorials and the binomial coefficient:
Full documentation is available online:
GCE-Math is a header-only library and does not require any additional libraries (beyond a C++11 compatible compiler). Simply add the header files to your project using:
#include "gcem.hpp"
You can install GCE-Math using the conda package manager.
conda install gcem -c kthohr
You can also install the library from source using CMake.
# clone gcem from GitHub
git clone https://github.com/kthohr/gcem ./gcem
# make a build directory
cd ./gcem
mkdir build
cd build
# generate Makefiles and install
cmake .. -DCMAKE_INSTALL_PREFIX=/gcem/install/location
make install
For example, /gcem/install/location
could be /usr/local/
.
There are two ways to build the test suite. On Unix-alike systems, a Makefile is available under tests/
.
cd ./gcem/tests
make
./run_tests
With CMake, the option BUILD_TESTS=1
generates the necessary Makefiles to build the test suite.
cd ./gcem
mkdir build
cd build
cmake ../ -DBUILD_TESTS=1 -DCMAKE_INSTALL_PREFIX=/gcem/install/location
make gcem_tests
cd tests
./exp.test
You can test the library online using an interactive Jupyter notebook:
GCE-Math functions are written as C++ templates with constexpr
specifiers, the format of which might be confusing to users unfamiliar with template-based programming. As an example, the Gaussian error function (erf
) is defined as:
template<typename T>
constexpr
return_t<T>
erf(const T x) noexcept;
where a set of internal templated constexpr
functions will implement a continued fraction expansion to return a value of type return_t<T>
. This output type ('return_t<T>
') is generally determined by the input type, e.g., int
, float
, double
, long double
, etc. When T
is an intergral type, the output will be upgraded to return_t<T> = double
, otherwise return_t<T> = T
. For types not covered by std::is_integral
, recasts should be used.
To calculate 10!:
#include "gcem.hpp"
int main()
{
constexpr int x = 10;
constexpr int res = gcem::factorial(x);
return 0;
}
Inspecting the assembly code generated by Clang:
_main: ## @main
.cfi_startproc
## BB#0:
push rbp
Lcfi0:
.cfi_def_cfa_offset 16
Lcfi1:
.cfi_offset rbp, -16
mov rbp, rsp
Lcfi2:
.cfi_def_cfa_register rbp
xor eax, eax
mov dword ptr [rbp - 4], 0
mov dword ptr [rbp - 8], 10
mov dword ptr [rbp - 12], 3628800
pop rbp
ret
.cfi_endproc
We see that a function call has been replaced by a numeric value (10! = 3628800).
Similarly, to compute the log Gamma function at a point:
#include "gcem.hpp"
int main()
{
constexpr long double x = 1.5;
constexpr long double res = gcem::lgamma(x);
return 0;
}
Assembly code:
LCPI0_0:
.long 1069547520 ## float 1.5
.section __TEXT,__literal16,16byte_literals
.p2align 4
LCPI0_1:
.quad -622431863250851168 ## x86_fp80 -0.120782237635245167208
.short 49147
.space 6
.section __TEXT,__text,regular,pure_instructions
.globl _main
.p2align 4, 0x90
_main: ## @main
.cfi_startproc
## BB#0:
push rbp
Lcfi0:
.cfi_def_cfa_offset 16
Lcfi1:
.cfi_offset rbp, -16
mov rbp, rsp
Lcfi2:
.cfi_def_cfa_register rbp
xor eax, eax
mov dword ptr [rbp - 4], 0
fld dword ptr [rip + LCPI0_0]
fstp xword ptr [rbp - 32]
fld xword ptr [rip + LCPI0_1]
fstp xword ptr [rbp - 48]
pop rbp
ret
.cfi_endproc
For a library built on the GCEM compile-time functionality, see StatsLib.