number—a number.
signed-prototype—a number.
signum
determines a numerical value that indicates whether
number is negative, zero, or positive.
For a rational,
signum
returns one of -1
, 0
, or 1
according to whether number is negative, zero, or positive.
For a float,
the result is a float of the same format
whose value is minus one, zero, or one.
For a complex number z
,
(signum
z)
is a complex number of the same phase but with unit magnitude,
unless z
is a complex zero, in which case the result is z
.
For rational arguments, signum
is a rational function,
but it may be irrational for complex arguments.
If number is a float, the result is a float. If number is a rational, the result is a rational. If number is a complex float, the result is a complex float. If number is a complex rational, the result is a complex, but it is implementation-dependent whether that result is a complex rational or a complex float.
(signum 0) → 0 (signum 99) → 1 (signum 4/5) → 1 (signum -99/100) → -1 (signum 0.0) → 0.0 (signum #c(0 33)) → #C(0.0 1.0) (signum #c(7.5 10.0)) → #C(0.6 0.8) (signum #c(0.0 -14.7)) → #C(0.0 -1.0) (eql (signum -0.0) -0.0) → true
Section 12.1.3.3 (Rule of Float Substitutability)
(signum x) ≡ (if (zerop x) x (/ x (abs x)))