exp2l
(3)base-2 exponential function
#include <math.h> double exp2(double x); float exp2f(float x); long double exp2l(long double x); Feature Test Macro Requirements for glibc (see feature_test_macros(7)): exp2(), exp2f(), exp2l(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L