Numbers in Emacs Lisp

Emacs Lisp uses IEEE standard. There’s nothing too much to say here. Let’s talk about some useful functions through examples.

isnan x

This predicate return t if the argument is NaN, nil otherwise.

frexp x

Return a cons cell (s . e) such that \(x = s \cdot 2^{e}\) and \(s \in [0.5, 1)\) if \(x\) is finite. If \(x\) is infinity or zero, then \(s=x\). Otherwise, \(x\) is NaN, \(s\) is also NaN.

logb x

Returns \(\log_{2} x\). If \(x=0\) or \(\infin\), then returns infinity; is \(x\) is NaN, then return NaN.

floatp obj

Test whether obj is a floating point number.

integerp obj

Test whether obj is an integer.

numberp obj

Test whether obj is an integer or a floating point.

natnump obj

Test whether obj is a natrual number.