.\"	$NetBSD: factor.6,v 1.18 2020/10/12 13:53:43 christos Exp $
.\"
.\" Copyright (c) 1989, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" Landon Curt Noll.
.\"
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.\" modification, are permitted provided that the following conditions
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.\"	@(#)factor.6	8.1 (Berkeley) 5/31/93
.\"
.\"
.\" By Landon Curt Noll, http://www.isthe.com/chongo/index.html /\oo/\
.\"
.Dd October 12, 2020
.Dt FACTOR 6
.Os
.Sh NAME
.Nm factor
.Nd factor a number
.Sh SYNOPSIS
.Nm
.Op Fl hx
.Op Ar number ...
.Sh DESCRIPTION
The
.Nm
utility factors integers larger than 
.Dv 0 .
When a number is factored, it is printed, followed by a
.Dq \&: ,
and the list of
.Pq prime
factors on a single line.
Factors are listed in ascending order, and are preceded by a space.
By default, if a factor divides a value more than once, it will be
printed more than once.
.Pp
When
.Nm
is invoked with one or more
.Ar number
arguments, each argument will be factored.
.Pp
When
.Nm
is invoked with no
.Ar number
arguments,
.Nm
reads numbers, one per line, from standard input, until end of file or error.
Leading white-space and empty lines are ignored.
Numbers may be preceded by a single +.
Numbers that start with
.Dv 0x
are interpreted as hexadecimal.
A 
.Dv 0
input exits the program.
Negative numbers are not allowed.
Numbers are terminated by a non-digit character (such as a newline).
After a number is read, it is factored.
Input lines must not be longer than
.Dv LINE_MAX \- 1
(currently 2047) characters.
.Pp
By default,
.Nm
is compiled against the OpenSSL bignum implementation
.Xr openssl_bn 3 ,
which lets it handle arbitrarily large values.
.Pq Note however that very large values can take a very long time to factor.
If
.Nm
is compiled without OpenSSL it is limited to the maximum value of
.Vt unsigned long .
.Pp
The following option is available:
.Bl -tag -width flag
.It Fl h
If the
.Fl h
flag is specified, factors will be printed in "human-readable" format.
If a factor x divides a value n (>1) times, it will appear as x^n.
.It Fl x
If the
.Fl x
flag is specified, factors will be printed in hexadecimal format.
.El
.Sh DIAGNOSTICS
Out of range or invalid input results in
an appropriate error message to standard error.
.Sh AUTHORS
Originally by
.An Landon Curt Noll .