/* $NetBSD: readhappy.c,v 1.1 2015/05/13 07:07:36 pgoyette Exp $ */
/*-
* Copyright (c) 2015 The NetBSD Foundation, Inc.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: readhappy.c,v 1.1 2015/05/13 07:07:36 pgoyette Exp $");
#include <sys/param.h>
#include <sys/conf.h>
#include <sys/device.h>
#include <sys/kernel.h>
#include <sys/module.h>
/*
* Create a device /dev/happy from which you can read sequential
* happy numbers.
*
* To use this device you need to do:
* mknod /dev/happy c 210 0
*
* Commentary:
* A happy number is a number defined by the following process: Starting with
* any positive integer, replace the number by the sum of the squares of its
* digits, and repeat the process until the number equals 1 (where it will
* stay), or it loops endlessly in a cycle which does not include 1. Those
* numbers for which this process ends in 1 are happy numbers, while those that
* do not end in 1 are unhappy numbers (or sad numbers).
*
* For more information on happy numbers, and the algorithms, see
* http://en.wikipedia.org/wiki/Happy_number
*
* The happy number generator is here only to have something that the user
* can read from our device. Any other arbitrary data generator could
* have been used. The algorithm is not critical to the implementation
* of the module.
*/
#define HAPPY_NUMBER 1
/* If n is not happy then its sequence ends in the cycle:
* 4, 16, 37, 58, 89, 145, 42, 20, 4, ... */
#define SAD_NUMBER 4
/* Calculate the sum of the squares of the digits of n */
static unsigned
dsum(unsigned n)
{
unsigned sum, x;
for (sum = 0; n; n /= 10) {
x = n % 10;
sum += x * x;
}
return sum;
}
static int
check_happy(unsigned n)
{
for (;;) {
unsigned total = dsum(n);
if (total == HAPPY_NUMBER)
return 1;
if (total == SAD_NUMBER)
return 0;
n = total;
}
}
dev_type_open(happy_open);
dev_type_close(happy_close);
dev_type_read(happy_read);
static struct cdevsw happy_cdevsw = {
.d_open = happy_open,
.d_close = happy_close,
.d_read = happy_read,
.d_write = nowrite,
.d_ioctl = noioctl,
.d_stop = nostop,
.d_tty = notty,
.d_poll = nopoll,
.d_mmap = nommap,
.d_kqfilter = nokqfilter,
.d_discard = nodiscard,
.d_flag = D_OTHER
};
struct happy_softc {
int refcnt;
unsigned last;
};
static struct happy_softc sc;
int
happy_open(dev_t self __unused, int flag __unused, int mode __unused,
struct lwp *l __unused)
{
if (sc.refcnt > 0)
return EBUSY;
sc.last = 0;
++sc.refcnt;
return 0;
}
int
happy_close(dev_t self __unused, int flag __unused, int mode __unused,
struct lwp *l __unused)
{
--sc.refcnt;
return 0;
}
int
happy_read(dev_t self __unused, struct uio *uio, int flags __unused)
{
char line[80];
/* Get next happy number */
while (check_happy(++sc.last) == 0)
continue;
/* Print it into line[] with trailing \n */
int len = snprintf(line, sizeof(line), "%u\n", sc.last);
/* Is there room? */
if (uio->uio_resid < len) {
--sc.last; /* Step back */
return EINVAL;
}
/* Send it to User-Space */
int e;
if ((e = uiomove(line, len, uio)))
return e;
return 0;
}
MODULE(MODULE_CLASS_MISC, happy, NULL);
static int
happy_modcmd(modcmd_t cmd, void *arg __unused)
{
/* The major should be verified and changed if needed to avoid
* conflicts with other devices. */
int cmajor = 210, bmajor = -1;
switch (cmd) {
case MODULE_CMD_INIT:
if (devsw_attach("happy", NULL, &bmajor, &happy_cdevsw,
&cmajor))
return ENXIO;
return 0;
case MODULE_CMD_FINI:
if (sc.refcnt > 0)
return EBUSY;
devsw_detach(NULL, &happy_cdevsw);
return 0;
default:
return ENOTTY;
}
}