Reciprocal square root

The evolved code is accurate to double precision

C Code derived from:

W. B. Langdon. Genetic Improvement of Data gives double precision invsqrt. In 7th edition of GI @ GECCO Companion 2019, pages 1709-1714, Prague, Czech Republic, 2019. ACM http://www.cs.ucl.ac.uk/staff/W.Langdon/ftp/papers/langdon_2019_GI7.pdf https://doi.org/10.1145/3319619.3326800

GGGP project at http://www.cs.ucl.ac.uk/staff/W.Langdon/gggp

Based on gi_cbrt.tar.gz README.txt 12 March 2020 gi_cbrt.tar.gz contains full results and code for several functions: only invsqrt is included here

Compiling

gcc -c invsqrt.c

to compile example:

gcc -c main.c; gcc invsqrt.o main.o -lm


Testing
~~~~~~~
./a.out 4
0.5 = invsqrt(4)