Procedure

     OPSGNI  ( Opposite Sign Integers )

     LOGICAL FUNCTION OPSGNI  ( X, Y )

Abstract

     Return .TRUE. if two given integer numbers have opposite signs.

Required_Reading

     None.

Keywords

     NUMBERS

Declarations

     IMPLICIT NONE

     INTEGER          X
     INTEGER          Y

Brief_I/O

     VARIABLE  I/O  DESCRIPTION
     --------  ---  --------------------------------------------------
     X          I   An integer.
     Y          I   An integer.

     The function returns .TRUE. when the integer numbers X and Y have
     opposite signs.

Detailed_Input

     X        is any integer number.

     Y        is any integer number.

Detailed_Output

     The function returns .TRUE. if one of the pair X,Y is positive and
     the other is negative. If either of the two values is zero, OPSGNI
     will be .FALSE.

Parameters

     None.

Exceptions

     Error free.

Files

     None.

Particulars

     This routine returns the value:

           (      (( X .GT. 0) .AND. (Y .LT. 0))
             .OR. (( X .LT. 0) .AND. (Y .GT. 0)) )

     This is a more stable value than

           ( X*Y .LT. 0 )

     Note that if either of the two values is zero, OPSGNI will be
     false.

Examples

     This routine can be used whenever a decision depends upon two
     integer values having opposite signs.

     IF ( OPSGNI ( F(X1), F(X2) ) ) THEN
           .
           .
        find the value of F closest to zero.
           .
           .
     ELSE
           .
           .
        do something
           .
           .
     END IF

Restrictions

     None.

Literature_References

     None.

Author_and_Institution

     J. Diaz del Rio    (ODC Space)
     B.V. Semenov       (JPL)
     W.L. Taber         (JPL)

Version

    SPICELIB Version 1.1.0, 26-OCT-2021 (JDR)

        Added IMPLICIT NONE statement.

        Edited the header to comply with NAIF standard. Extended
        $Detailed_Output section to indicate the output value for
        the case of either input being zero.

    SPICELIB Version 1.0.2, 07-NOV-2005 (BVS)

        Fixed cut-and-paste errors in the header.

    SPICELIB Version 1.0.1, 10-MAR-1992 (WLT)

        Comment section for permuted index source lines was added
        following the header.

    SPICELIB Version 1.0.0, 31-JAN-1990 (WLT)