CLHS: Function SIGNUM

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Function SIGNUM

Syntax:

signum number => signed-prototype

Arguments and Values:

number---a number.

signed-prototype---a number.

Description:

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.

Examples:

     (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

Side Effects: None.

Affected By: None.

Exceptional Situations: None.

See Also:

Section 12.1.3.3 (Rule of Float Substitutability)

Notes:

     (signum x) ==  (if (zerop x) x (/ x (abs x)))

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