TOMS577, a C library which evaluates Carlson's elliptic integral functions RC, RD, RF and RJ.
TOMS577 is available in a C version and a FORTRAN77 version and a FORTRAN90 version and a MATLAB version and a Python version.
ELLIPTIC_INTEGRAL, a C library which evaluates complete elliptic integrals of first, second and third kind, using Carlson's elliptic integral functions.
SPECIAL_FUNCTIONS, a C library which evaluates special functions, including Airy, Associated Legendre Bessel, Beta, Complete Elliptic Integral, Confluent Hypergeometric, Cosine Integral, Elliptic Integral, Error, Exponential Integral, Fresnel Integral, Gamma, Hankel, Hypergeometric, Incomplete Beta, Incomplete Gamma, Jacobian Elliptic, Kelvin, Lambda, Legendre, Mathieu, Modified Spherical Bessel, Parabolic Cylinder, Psi, Riccati-Bessel, Sine Integral, Spheroidal Wave, Struve, Whittaker, as well as Bernoulli Numbers, Euler Numbers, Hermite Polynomials, Laguerre Polynomials, Legendre Polynomials, by Shanjie Zhang, Jianming Jin;
TEST_VALUES, a C library which supplies test values of various mathematical functions.
You can go up one level to the C source codes.