log1pf(3) -- Linux man page
NAMElog1p - logarithm of 1 plus argument
#include <math.h> double log1p(double x); float log1pf(float x); long double log1pl(long double x);
DESCRIPTIONlog1p(x) returns a value equivalent to `log (1 + x)'. It is computed in a way that is accurate even if the value of x is near zero.
CONFORMING TOBSD, C99. The float and the long double variants are C99 requirements.
SEE ALSOexp(3), log(3), expm1(3)