PHP Manual . Prev . Next . PHP 4 >= 4.1.0) log1p -- Returns log(1 + number), computed in a way that accurate even when the val ue of number is close to zero . float log1p ( float number) . Warning . This function is EXPERIMENTAL . The behaviour of this function, the name of this function, and anything else documented about this function may change in a future release of PHP without notice. ... This function is currently not documented, only the argument list is available. ...