NAME
    fact - factorial

SYNOPSIS
    fact(x)

TYPES
    x		int

    return	int

DESCRIPTION
    Return the factorial of a number.  Factorial is defined as:

	   x! = 1 * 2 * 3 * ... * x-1 * x
	   0! = 1

EXAMPLE
    > print fact(10), fact(5), fact(2), fact(1), fact(0)
    3628800 120 2 1 1

    > print fact(40)
    815915283247897734345611269596115894272000000000

LIMITS
    2^24 > x >= 0
    y < 2^24

LIBRARY
    void zfact(NUMBER x, *ret)

SEE ALSO
    comb, perm