factor/factor.6

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   4 .\"     The Regents of the University of California.  All rights reserved.
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   6 .\" This code is derived from software contributed to Berkeley by
   7 .\" Landon Curt Noll.
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  32 .\"
  33 .\"     @(#)factor.6    8.1 (Berkeley) 5/31/93
  34 .\"
  35 .\"
  36 .\" By Landon Curt Noll, http://www.isthe.com/chongo/index.html /\oo/\
  37 .\"
  38 .Dd October 12, 2020
  39 .Dt FACTOR 6
  40 .Os
  41 .Sh NAME
  42 .Nm factor
  43 .Nd factor a number
  44 .Sh SYNOPSIS
  45 .Nm
  46 .Op Fl hx
  47 .Op Ar number ...
  48 .Sh DESCRIPTION
  49 The
  50 .Nm
  51 utility factors integers larger than
  52 .Dv 0 .
  53 When a number is factored, it is printed, followed by a
  54 .Dq \&: ,
  55 and the list of
  56 .Pq prime
  57 factors on a single line.
  58 Factors are listed in ascending order, and are preceded by a space.
  59 By default, if a factor divides a value more than once, it will be
  60 printed more than once.
  61 .Pp
  62 When
  63 .Nm
  64 is invoked with one or more
  65 .Ar number
  66 arguments, each argument will be factored.
  67 .Pp
  68 When
  69 .Nm
  70 is invoked with no
  71 .Ar number
  72 arguments,
  73 .Nm
  74 reads numbers, one per line, from standard input, until end of file or error.
  75 Leading white-space and empty lines are ignored.
  76 Numbers may be preceded by a single +.
  77 Numbers that start with
  78 .Dv 0x
  79 are interpreted as hexadecimal.
  80 A
  81 .Dv 0
  82 input exits the program.
  83 Negative numbers are not allowed.
  84 Numbers are terminated by a non-digit character (such as a newline).
  85 After a number is read, it is factored.
  86 Input lines must not be longer than
  87 .Dv LINE_MAX \- 1
  88 (currently 2047) characters.
  89 .Pp
  90 By default,
  91 .Nm
  92 is compiled against the OpenSSL bignum implementation
  93 .Xr openssl_bn 3 ,
  94 which lets it handle arbitrarily large values.
  95 .Pq Note however that very large values can take a very long time to factor.
  96 If
  97 .Nm
  98 is compiled without OpenSSL it is limited to the maximum value of
  99 .Vt unsigned long .
 100 .Pp
 101 The following option is available:
 102 .Bl -tag -width flag
 103 .It Fl h
 104 If the
 105 .Fl h
 106 flag is specified, factors will be printed in "human-readable" format.
 107 If a factor x divides a value n (>1) times, it will appear as x^n.
 108 .It Fl x
 109 If the
 110 .Fl x
 111 flag is specified, factors will be printed in hexadecimal format.
 112 .El
 113 .Sh DIAGNOSTICS
 114 Out of range or invalid input results in
 115 an appropriate error message to standard error.
 116 .Sh AUTHORS
 117 Originally by
 118 .An Landon Curt Noll .