NAME
    isprime - whether a small integer is prime

SYNOPSIS
    isprime(x [,err])

TYPES
    x		int
    err		int

    return	int

DESCRIPTION
    Determine if x is is a small prime.  This function will return
    1 if x is a small prime.  If x is even, this function will
    return 0.  If x is negative or a small composite (non-prime),
    0 will be returned.

    If x is a large positive odd value and the err argument is
    given, this function return err.  If x is a large positive odd
    value and the err argument is not given, an error will be
    generated.

    Note that normally this function returns the integer 0 or 1.
    If err is given and x is a large positive odd value, then err
    will be returned.

EXAMPLE
    > print isprime(-3), isprime(1), isprime(2)
    0 0 1

    > print isprime(21701), isprime(1234577), isprime(1234579)
    1 1 0

    > print isprime(2^31-9), isprime(2^31-1), isprime(2^31+11)
    0 1 1

    > print isprime(2^32+1, -1), isprime(3^99, 2), isprime(4^99, 2)
    -1 2 0

LIMITS
    err not given  and  (y is even  or  y < 2^32)

LIBRARY
    FLAG zisprime(ZVALUE x)	(return 1 if prime, 0 not prime, -1 if >= 2^32)

SEE ALSO
    factor, lfactor, nextprime, prevprime, pfact, pix