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)

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

SEE ALSO
    factor, lfactor, nextcand, nextprime, prevcand, prevprime,
    pfact, pix, ptest

## Copyright (C) 1999-2006  Landon Curt Noll
##
## Calc is open software; you can redistribute it and/or modify it under
## the terms of the version 2.1 of the GNU Lesser General Public License
## as published by the Free Software Foundation.
##
## Calc is distributed in the hope that it will be useful, but WITHOUT
## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
## or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General
## Public License for more details.
##
## A copy of version 2.1 of the GNU Lesser General Public License is
## distributed with calc under the filename COPYING-LGPL.  You should have
## received a copy with calc; if not, write to Free Software Foundation, Inc.
## 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
##
## Under source code control:   1994/10/21 02:21:29
## File existed as early as:    1994
##
## chongo <was here> /\oo/\     http://www.isthe.com/chongo/
## Share and enjoy!  :-)        http://www.isthe.com/chongo/tech/comp/calc/
