coreutils/src/factor.c

/* factor -- print prime factors of n.
   Copyright (C) 86, 1995-2001 Free Software Foundation, Inc.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2, or (at your option)
   any later version.

   This program 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 General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software Foundation,
   Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */

/* Written by Paul Rubin <phr@ocf.berkeley.edu>.
   Adapted for GNU, fixed to factor UINT_MAX by Jim Meyering.  */

#include <config.h>
#include <stdio.h>
#include <sys/types.h>

#include <assert.h>
#define NDEBUG 1

#include "system.h"
#include "closeout.h"
#include "error.h"
#include "human.h"
#include "long-options.h"
#include "readtokens.h"
#include "xstrtol.h"

/* The official name of this program (e.g., no `g' prefix).  */
#define PROGRAM_NAME "factor"

#define AUTHORS "Paul Rubin"

/* Token delimiters when reading from a file.  */
#define DELIM "\n\t "

/* FIXME: if this program is ever modified to factor integers larger
   than 2^128, this constant (and the algorithm :-) will have to change.  */
#define MAX_N_FACTORS 128

/* The trial divisor increment wheel.  Use it to skip over divisors that
   are composites of 2, 3, 5, 7, or 11.  The part from WHEEL_START up to
   WHEEL_END is reused periodically, while the "lead in" is used to test
   for those primes and to jump onto the wheel.  For more information, see
   http://www.utm.edu/research/primes/glossary/WheelFactorization.html  */

#include "wheel-size.h"  /* For the definition of WHEEL_SIZE.  */
static const unsigned int wheel_tab[] =
  {
#include "wheel.h"
  };

#define WHEEL_START (wheel_tab + WHEEL_SIZE)
#define WHEEL_END (wheel_tab + (sizeof wheel_tab / sizeof wheel_tab[0]))

/* The name this program was run with. */
char *program_name;

void
usage (int status)
{
  if (status != 0)
    fprintf (stderr, _("Try `%s --help' for more information.\n"),
	     program_name);
  else
    {
      printf (_("\
Usage: %s [NUMBER]...\n\
  or:  %s OPTION\n\
"),
	      program_name, program_name);
      printf (_("\
Print the prime factors of each NUMBER.\n\
\n\
  --help      display this help and exit\n\
  --version   output version information and exit\n\
\n\
  Print the prime factors of all specified integer NUMBERs.  If no arguments\n\
  are specified on the command line, they are read from standard input.\n\
"));
      puts (_("\nReport bugs to <bug-sh-utils@gnu.org>."));
    }
  exit (status);
}

/* FIXME: comment */

static int
factor (uintmax_t n0, int max_n_factors, uintmax_t *factors)
{
  register uintmax_t n = n0, d, q;
  int n_factors = 0;
  unsigned int const *w = wheel_tab;

  if (n < 1)
    return n_factors;

  /* The exit condition in the following loop is correct because
     any time it is tested one of these 3 conditions holds:
      (1) d divides n
      (2) n is prime
      (3) n is composite but has no factors less than d.
     If (1) or (2) obviously the right thing happens.
     If (3), then since n is composite it is >= d^2. */

  d = 2;
  do
    {
      q = n / d;
      while (n == q * d)
	{
	  assert (n_factors < max_n_factors);
	  factors[n_factors++] = d;
	  n = q;
	  q = n / d;
	}
      d += *(w++);
      if (w == WHEEL_END)
	w = WHEEL_START;
    }
  while (d <= q);

  if (n != 1 || n0 == 1)
    {
      assert (n_factors < max_n_factors);
      factors[n_factors++] = n;
    }

  return n_factors;
}

/* FIXME: comment */

static int
print_factors (const char *s)
{
  uintmax_t factors[MAX_N_FACTORS];
  uintmax_t n;
  int n_factors;
  int i;
  char buf[LONGEST_HUMAN_READABLE + 1];

  if (xstrtoumax (s, NULL, 10, &n, "") != LONGINT_OK)
    {
      error (0, 0, _("`%s' is not a valid positive integer"), s);
      return 1;
    }
  n_factors = factor (n, MAX_N_FACTORS, factors);
  printf ("%s:", human_readable (n, buf, 1, 1));
  for (i = 0; i < n_factors; i++)
    printf (" %s", human_readable (factors[i], buf, 1, 1));
  putchar ('\n');
  return 0;
}

static int
do_stdin (void)
{
  int fail = 0;
  token_buffer tokenbuffer;

  init_tokenbuffer (&tokenbuffer);

  for (;;)
    {
      long int token_length;

      token_length = readtoken (stdin, DELIM, sizeof (DELIM) - 1,
				&tokenbuffer);
      if (token_length < 0)
	break;
      fail |= print_factors (tokenbuffer.buffer);
    }
  free (tokenbuffer.buffer);

  return fail;
}

int
main (int argc, char **argv)
{
  int fail;

  program_name = argv[0];
  setlocale (LC_ALL, "");
  bindtextdomain (PACKAGE, LOCALEDIR);
  textdomain (PACKAGE);

  atexit (close_stdout);

  parse_long_options (argc, argv, PROGRAM_NAME, GNU_PACKAGE, VERSION,
		      AUTHORS, usage);
  /* The above handles --help and --version.
     Since there is no other invocation of getopt, handle `--' here.  */
  if (argc > 1 && STREQ (argv[1], "--"))
    {
      --argc;
      ++argv;
    }

  fail = 0;
  if (argc == 1)
    fail = do_stdin ();
  else
    {
      int i;
      for (i = 1; i < argc; i++)
	fail |= print_factors (argv[i]);
    }
  if (fail)
    usage (1);

  exit (fail);
}