#    isgn --Calculates sign of (-1)**input-integer
# 
#    Description:
#    ------------
#    This function calculates the value of -1 raised to the power of the
#    input integer without using exponentiation. It is based on the fact
#    that if the input integer is even, the result will be +1.
#
#
#        Version    Date        Author     Description
#	         27-JAN-1993  R. Williamson Converted to SPP
#           2    17-AUG-1983  PAT MURPHY   PDL and Fortran code added
#           1    17-AUG-1983  PAT MURPHY   Prolog Generation


int procedure isgn (n)

int n,isn                                   #  The input exponent

begin
        #  Set the result negative
        isn = -1
        #  unless the input is even
        if(int(n/2)*2==n)isn = 1

return (isn)
end