MODULE irbit1

    LIBRARY "funlib"
    DECLARE FUNCTION and, or, nott

    SHARE ib1, ib3, ib5, ib14, two14, iseed, iff

    LET iff = 0
    LET ib1 = 2^0
    LET ib3 = 2^2
    LET ib5 = 2^4
    LET ib14 = 2^13
    LET two14 = 2^14

    FUNCTION irbit1 (iiseed)

        ! The argument iiseed is the seed only on the first use.
        ! On subsequent use, the shared iseed is used.

        IF iff=0 then
           LET iseed = iiseed
           LET iff = 1
        END IF

        ! Here, newbit = 1 means true, = -1 means false

        LET newbit = 2*sgn(and(iseed, ib14)) - 1
        IF and(iseed, ib5) <> 0 then LET newbit = -newbit
        IF and(iseed, ib3) <> 0 then LET newbit = -newbit
        IF and(iseed, ib1) <> 0 then LET newbit = -newbit
        IF iseed > two14 then LET iseed = iseed - two14
        LET iseed = 2 * iseed
        IF newbit=1 then
           LET irbit1 = 1
           LET iseed = iseed + ib1     ! Just use +
        ELSE
           LET irbit1 = 0
        END IF

    END FUNCTION

END MODULE