log
Returns the natural logarithm (base e) of its argument.
Returns the natural logarithm of EXPR, or $_ if omitted. The argument
is coerced to Nv (f64). Returns -Inf for 0 and NaN for negative
values. For other bases use log($x) / log($base). Always returns an Nv.
Synopsis
my $l = log(exp(1)); # 1
my $l = log($x);
my $l = log; # log($_)