
sgn(+Number, -Result)

   Unifies Result with the sign of Number which is either -1, 0 or 1.



Arguments
   Number              A number.
   Result              Output: an integer.

Type
   Arithmetic

Description
   This predicate is used by the ECLiPSe compiler to expand evaluable
   arithmetic expressions.  So the call to sgn(Number, Result) is
   equivalent to

    Result is sgn(Number)

    which should be preferred for portability.

   sgn/2 gives the integer -1 if Number is negative, 0 if it is zero and 1
   if it is greater than zero.  It is always true that

    X =:= sgn(X) * abs(X)

   Caution: this operation does not distinguish between +0.0 and -0.0.
   See copysign/3 for an alternative.

   In coroutining mode, if Number is uninstantiated, the call to sgn/2 is
   delayed until this variable is instantiated.


Modes and Determinism
   sgn(+, -) is det

Exceptions
     4 --- Number is not instantiated (non-coroutining mode only).
    24 --- Number is not of a numeric type.

Examples
   
    Result is sgn(42).		% gives Result = 1
    Result is sgn(-5).		% gives Result = -1
    Result is sgn(-6.2).	% gives Result = -1
    Result is sgn(0.0).		% gives Result = 0
    Result is sgn(-0.0).	% gives Result = 0


See Also
   is / 2, abs / 2, copysign / 3
