/*
 * Copyright 1990, 1998  The Open Group
 *
 * Permission to use, copy, modify, distribute, and sell this software and its
 * documentation for any purpose is hereby granted without fee, provided that
 * the above copyright notice appear in all copies and that both that
 * copyright notice and this permission notice appear in supporting
 * documentation.
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE OPEN GROUP BE LIABLE FOR ANY CLAIM, DAMAGES OR
 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 *
 * Except as contained in this notice, the name of The Open Group shall
 * not be used in advertising or otherwise to promote the sale, use or
 * other dealings in this Software without prior written authorization
 * from The Open Group.
 *
 */

/*
 * Copyright (c) 2005, Oracle and/or its affiliates. All rights reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 */

/*
 * Author:  Keith Packard, MIT X Consortium
 * Lastlog support and dynamic utmp entry allocation
 *   by Andreas Stolcke <stolcke@icsi.berkeley.edu>
 */

/*
 * sessreg
 *
 * simple wtmp/utmp frobber
 *
 * usage: sessreg [ -w <wtmp-file> ] [ -u <utmp-file> ]
 *		  [ -l <line> ]
 *		  [ -L <lastlog-file> ]		      / #ifdef USE_LASTLOG
 *		  [ -h <host-name> ]				/ BSD only
 *		  [ -s <slot-number> ] [ -x Xservers-file ]	/ BSD only
 *		  [ -t <ttys-file> ]				/ BSD only
 *		  [ -a ] [ -d ] user-name
 *
 * one of -a or -d must be specified
 */

#include "sessreg.h"

#include <X11/Xos.h>
#include <X11/Xfuncs.h>
#include <X11/Xfuncproto.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#ifdef USE_UTMP
static void set_utmp (struct utmp *u, char *line, char *user, char *host,
		      time_t date, int addp);
#endif

#ifdef USE_UTMPX
static void set_utmpx (struct utmpx *u, const char *line, const char *user,
		       const char *host, time_t date, int addp);
#endif

#ifdef HAVE_STRUCT_UTMP_UT_ID
/* used for hashing ut_id */
typedef  unsigned long  int  ub4;   /* unsigned 4-byte quantities */
typedef  unsigned       char ub1;   /* unsigned 1-byte quantities */

#define hashsize(n) ((ub4)1<<(n))
#define hashmask(n) (hashsize(n)-1)

ub4 hash(register ub1 *k, register ub4 length, register ub4 initval);

#endif

static int wflag, uflag, lflag;
static const char *wtmp_file, *utmp_file;
#ifdef USE_UTMPX
#ifdef HAVE_UPDWTMPX
static const char *wtmpx_file = NULL;
#endif
#ifdef HAVE_UTMPXNAME
static const char *utmpx_file = NULL;
#endif
#endif

static int utmp_none, wtmp_none;
/*
 * BSD specific variables.  To make life much easier for Xstartup/Xreset
 * maintainers, these arguments are accepted but ignored for sysV
 */
static int hflag, xflag, tflag;
static char *host_name = NULL;
#if defined(USE_UTMP) && !defined(HAVE_PUTUTLINE)
static int sflag;
static int slot_number;
#endif
static char *xservers_file, *ttys_file;
static char *user_name;
static int aflag, dflag;
#ifdef USE_LASTLOG
static const char *llog_file;
static int llog_none, Lflag;
#endif

static char *program_name;

#if defined(USE_UTMP) && !defined(HAVE_PUTUTLINE)
static int findslot (char *line_name, char *host_name, int addp, int slot);
static int Xslot (char *ttys_file, char *servers_file, char *tty_line,
		  char *host_name, int addp);
#endif

static void _X_NORETURN _X_COLD
usage (int x)
{
	fprintf (stderr,
		 "%s: usage %s {-a -d} [-w wtmp-file] [-u utmp-file]"
#ifdef USE_LASTLOG
		 " [-L lastlog-file]"
#endif
		 "\n"
		 "             [-t ttys-file] [-l line-name] [-h host-name] [-V]\n"
		 "             [-s slot-number] [-x servers-file] user-name\n",
		 program_name, program_name);
	exit (x);
}

static char *
getstring (char ***avp, int *flagp)
{
	char	**a = *avp;
	char	*flag = *a;

	if (*flagp != 0) {
		fprintf (stderr, "%s: cannot give more than one -%s option\n",
			 program_name, flag);
		usage (1);
	}
	*flagp = 1;
	/* if the argument is given immediately following the flag,
	   i.e. "sessreg -hfoo ...", not "sessreg -h foo ...",
	   then return the rest of the string as the argument value */
	if (*++*a)
		return *a;
	/* else use the next pointer in the argv list as the argument value */
	++a;
	if (!*a) {
		fprintf (stderr, "%s: -%s requires an argument\n",
			 program_name, flag);
		usage (1);
	}
	*avp = a;
	return *a;
}

#if defined(USE_UTMP) && !defined(HAVE_PUTUTLINE)
static int
syserr (int x, const char *s)
{
	if (x == -1) {
		perror (s);
		exit (1);
	}
	return x;
}
#endif

static int
sysnerr (int x, const char *s)
{
	if (x == 0) {
		perror (s);
		exit (1);
	}
	return x;
}

/*
 * While this looks like it could be replaced with strlcpy() on platforms
 * that have it, we're sticking with strncpy() so that we zero out the
 * whole buffer to avoid writing garbage to the fixed length fields in the
 * utmp/wtmp files, since strlcpy() does not write past the \0 terminator.
 */
static void
safe_strncpy(char *dest, const char *src, size_t n)
{
    (void)strncpy(dest, src, n);
    if (n > 0)
        dest[n - 1] = '\0';
}

int
main (int argc, char **argv)
{
#if defined(USE_UTMP) && !defined(HAVE_PUTUTLINE)
	int		utmp;
#endif
#ifndef USE_UTMPX
	int		wtmp;
#endif
	time_t		current_time;
#ifdef USE_UTMP
	struct utmp	utmp_entry;
#endif
#ifdef USE_UTMPX
	struct utmpx	utmpx_entry;
#endif
	char *		line = NULL;

	program_name = argv[0];
	while (*++argv && **argv == '-') {
		switch (*++*argv) {
		case 'w':
			wtmp_file = getstring (&argv, &wflag);
			if (!strcmp (wtmp_file, "none"))
				wtmp_none = 1;
#if defined(USE_UTMPX) && defined(HAVE_UPDWTMPX)
			else
				wtmpx_file = wtmp_file;
#endif
			break;
		case 'u':
			utmp_file = getstring (&argv, &uflag);
			if (!strcmp (utmp_file, "none"))
				utmp_none = 1;
#if defined(USE_UTMPX) && defined(HAVE_UTMPXNAME)
			else
				utmpx_file = utmp_file;
#endif
			break;
#ifdef USE_LASTLOG
		case 'L':
			llog_file = getstring (&argv, &Lflag);
			if (!strcmp (llog_file, "none"))
				llog_none = 1;
			break;
#endif
		case 't':
			ttys_file = getstring (&argv, &tflag);
			break;
		case 'l':
			line = getstring (&argv, &lflag);
			break;
		case 'h':
			host_name = getstring (&argv, &hflag);
			break;
		case 's':
#if defined(USE_UTMP) && !defined(HAVE_PUTUTLINE)
			slot_number = atoi (getstring (&argv, &sflag));
#endif
			break;
		case 'x':
			xservers_file = getstring (&argv, &xflag);
			break;
		case 'a':
			aflag++;
			break;
		case 'd':
			dflag++;
			break;
		case 'V':
			printf("%s\n", PACKAGE_STRING);
			exit (0);
		default:
			fprintf (stderr, "%s: unrecognized option '%s'\n",
				 program_name, argv[0]);
			usage (1);
		}
	}
	user_name = *argv++;
	if (user_name == NULL) {
		fprintf (stderr, "%s: missing required user-name argument\n",
			 program_name);
		usage (1);
	}
	if (*argv != NULL) {
		fprintf (stderr, "%s: unrecognized argument '%s'\n",
			 program_name, argv[0]);
		usage (1);
	}
	/*
	 * complain if neither aflag nor dflag are set,
	 * or if both are set.
	 */
	if (!(aflag ^ dflag)) {
		fprintf (stderr, "%s: must specify exactly one of -a or -d\n",
			 program_name);
		usage (1);
	}
	if (xflag && !lflag) {
		fprintf (stderr, "%s: must specify -l when -x is used\n",
			 program_name);
		usage (1);
	}
	/* set up default file names */
	if (!wflag) {
		wtmp_file = WTMP_FILE;
#if defined(USE_UTMPX) && defined(HAVE_UPDWTMPX)
		wtmpx_file = WTMPX_FILE;
#endif
	}
	if (!uflag) {
		utmp_file = UTMP_FILE;
#if defined(USE_UTMPX) && defined(HAVE_UTMPXNAME)
		utmpx_file = UTMPX_FILE;
#endif
	}
#ifdef USE_LASTLOG
	if (!Lflag)
		llog_file = LLOG_FILE;
#endif
#if defined(USE_UTMP) && !defined(HAVE_PUTUTLINE)
	if (!tflag)
		ttys_file = TTYS_FILE;
	if (!sflag && !utmp_none) {
		if (xflag)
			sysnerr (slot_number = Xslot (ttys_file, xservers_file, line, host_name, aflag), "Xslot");
		else
			sysnerr (slot_number = ttyslot (), "ttyslot");
	}
#endif
	if (!lflag) {
		sysnerr ((line = ttyname (0)) != NULL, "ttyname");
		if (strncmp(line, "/dev/", 5) == 0)
			line += 5;
	}
	time (&current_time);
#ifdef USE_UTMP
	set_utmp (&utmp_entry, line, user_name, host_name, current_time, aflag);
#endif

#ifdef USE_UTMPX
	/* need to set utmpxname() before calling set_utmpx() for
	   UtmpxIdOpen to work */
# ifdef HAVE_UTMPXNAME
	if (utmpx_file != NULL) {
		utmpxname (utmpx_file);
	}
# endif
	set_utmpx (&utmpx_entry, line, user_name,
		   host_name, current_time, aflag);
#endif

	if (!utmp_none) {
#ifdef USE_UTMPX
# ifdef HAVE_UTMPXNAME
		if (utmpx_file != NULL)
# endif
		{
			setutxent ();
			(void) getutxid (&utmpx_entry);
			pututxline (&utmpx_entry);
			endutxent ();
		}
#endif
#ifdef USE_UTMP
# ifdef HAVE_PUTUTLINE
		utmpname (utmp_file);
		setutent ();
		(void) getutid (&utmp_entry);
		pututline (&utmp_entry);
		endutent ();
# else
		utmp = open (utmp_file, O_RDWR);
		if (utmp != -1) {
			syserr ((int) lseek (utmp, (off_t) slot_number * sizeof (struct utmp), 0), "lseek");
			sysnerr (write (utmp, (char *) &utmp_entry, sizeof (utmp_entry))
					== sizeof (utmp_entry), "write utmp entry");
			close (utmp);
		}
# endif
#endif /* USE_UTMP */
	}
	if (!wtmp_none) {
#ifdef USE_UTMPX
# ifdef HAVE_UPDWTMPX
		if (wtmpx_file != NULL) {
			updwtmpx(wtmpx_file, &utmpx_entry);
		}
# endif
#else
		wtmp = open (wtmp_file, O_WRONLY|O_APPEND);
		if (wtmp != -1) {
			sysnerr (write (wtmp, (char *) &utmp_entry, sizeof (utmp_entry))
					== sizeof (utmp_entry), "write wtmp entry");
			close (wtmp);
		}
#endif
	}
#ifdef USE_LASTLOG
	if (aflag && !llog_none) {
		int llog;
		struct passwd *pwd = getpwnam(user_name);

		sysnerr( pwd != NULL, "get user id");
		llog = open (llog_file, O_RDWR);

		if (llog != -1) {
			struct lastlog ll;

			sysnerr (lseek(llog, (off_t) (pwd->pw_uid*sizeof(ll)), 0)
					!= -1, "seeking lastlog entry");
			memset(&ll, 0, sizeof(ll));
			ll.ll_time = current_time;
			if (line)
			 safe_strncpy (ll.ll_line, line, sizeof (ll.ll_line));
			if (host_name)
			 safe_strncpy (ll.ll_host, host_name, sizeof (ll.ll_host));

			sysnerr (write (llog, (char *) &ll, sizeof (ll))
					== sizeof (ll), "write lastlog entry");
			close (llog);
		}
	}
#endif
	return 0;
}

/*
 * fill in the appropriate records of the utmp entry
 */

#ifdef USE_UTMP
static void
set_utmp (struct utmp *u, char *line, char *user, char *host, time_t date, int addp)
{
	memset (u, 0, sizeof (*u));
	if (line)
		safe_strncpy (u->ut_line, line, sizeof (u->ut_line));
	else
		memset (u->ut_line, 0, sizeof (u->ut_line));
	if (addp && user)
		safe_strncpy (u->ut_name, user, sizeof (u->ut_name));
	else
		memset (u->ut_name, 0, sizeof (u->ut_name));
#ifdef HAVE_STRUCT_UTMP_UT_ID
	if (line) {
		/*
		 * The ut_id is 4 bytes long.  We make a hash of the line
		 * received, preceding it by ":" to prevent clashing with
		 * other ut_ids.
		 */
		ub4 h;
		u->ut_id[0]=':';
		h = hash(line, strlen(line),0x9e3779b9);
		h = (h & hashmask((sizeof(u->ut_id)-sizeof(char))*8));
		(void) strncpy (u->ut_id + 1,(char *) &h,  sizeof (u->ut_id)-sizeof(char));
	} else
		/*
		 * From utmp(5):
		 * Clearing ut_id may result in race conditions leading to corrupted
		 * utmp entries and and potential security holes.
		 */
	        /* TODO: CHECK this  */
		memset (u->ut_id, 0, sizeof (u->ut_id));
#endif
#ifdef HAVE_STRUCT_UTMP_UT_PID
	if (addp)
		u->ut_pid = getppid ();
	else
		u->ut_pid = 0;
#endif
#ifdef HAVE_STRUCT_UTMP_UT_TYPE
	if (addp)
		u->ut_type = USER_PROCESS;
	else
		u->ut_type = DEAD_PROCESS;
#endif
#ifdef HAVE_STRUCT_UTMP_UT_HOST
	if (addp && host)
		safe_strncpy (u->ut_host, host, sizeof (u->ut_host));
	else
		memset (u->ut_host, 0, sizeof (u->ut_host));
#endif
	u->ut_time = date;
}
#endif /* USE_UTMP */

#ifdef USE_UTMPX
static int
UtmpxIdOpen( char *utmpId )
{
	struct utmpx *u;	/* pointer to entry in utmp file           */
	int    status = 1;	/* return code                             */

	setutxent();

	while ( (u = getutxent()) != NULL ) {

		if ( (strncmp(u->ut_id, utmpId, 4) == 0 ) &&
		     u->ut_type != DEAD_PROCESS ) {

			status = 0;
			break;
		}
	}

	endutxent();
	return (status);
}

static void
set_utmpx (struct utmpx *u, const char *line, const char *user,
	   const char *host, time_t date, int addp)
{
	static const char letters[] =
	       "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";

	memset (u, 0, sizeof (*u));
	if (line)
	{
		if(strcmp(line, ":0") == 0)
			(void) strcpy(u->ut_line, "console");
		else
			safe_strncpy (u->ut_line, line, sizeof (u->ut_line));

		safe_strncpy(u->ut_host, line, sizeof(u->ut_host));
#ifdef HAVE_STRUCT_UTMPX_UT_SYSLEN
		u->ut_syslen = strlen(line);
#endif
	}
	else
		memset (u->ut_line, 0, sizeof (u->ut_line));
	if (addp && user)
		safe_strncpy (u->ut_user, user, sizeof (u->ut_user));
	else
		memset (u->ut_user, 0, sizeof (u->ut_user));

	if (line) {
		size_t	i;
		/*
		 * this is a bit crufty, but
		 * follows the apparent conventions in
		 * the ttys file.  ut_id is only 4 bytes
		 * long, and the last 4 bytes of the line
		 * name are written into it, left justified.
		 */
		i = strlen (line);
		if (i >= sizeof (u->ut_id))
			i -= sizeof (u->ut_id);
		else
			i = 0;
		safe_strncpy (u->ut_id, line + i, sizeof (u->ut_id));

		/* make sure there is no entry using identical ut_id */
		if (!UtmpxIdOpen(u->ut_id) && addp) {
			int limit = sizeof(letters) - 1;
			int t = 0;

			u->ut_id[1] = line[i];
			u->ut_id[2] = line[i+1];
			u->ut_id[3] = line[i+2];
			do {
				u->ut_id[0] = letters[t];
				t++;
			} while (!UtmpxIdOpen(u->ut_id) && (t < limit));
		}
		if (!addp && strstr(line, ":") != NULL) {
			struct utmpx *tmpu;

			while ( (tmpu = getutxent()) != NULL ) {
				if ( (strcmp(tmpu->ut_host, line) == 0 ) &&
					tmpu->ut_type != DEAD_PROCESS ) {
					strncpy(u->ut_id, tmpu->ut_id,
						sizeof(u->ut_id));
					break;
				}
			}
			endutxent();
		}
	} else
		memset (u->ut_id, 0, sizeof (u->ut_id));

	if (addp) {
		u->ut_pid = getppid ();
		u->ut_type = USER_PROCESS;
	} else {
		u->ut_pid = 0;
		u->ut_type = DEAD_PROCESS;
	}
	u->ut_tv.tv_sec = date;
	u->ut_tv.tv_usec = 0;
}
#endif /* USE_UTMPX */

#if defined(USE_UTMP) && !defined(HAVE_PUTUTLINE)
/*
 * compute the slot-number for an X display.  This is computed
 * by counting the lines in /etc/ttys and adding the line-number
 * that the display appears on in Xservers.  This is a poor
 * design, but is limited by the non-existant interface to utmp.
 * If host_name is non-NULL, assume it contains the display name,
 * otherwise use the tty_line argument (i.e., the tty name).
 */

static int
Xslot (char *ttys_file, char *servers_file, char *tty_line, char *host_name,
       int addp)
{
	FILE	*ttys, *servers;
	int	c;
	int	slot = 1;
	int	column0 = 1;
	char	servers_line[1024];
	char	disp_name[512];
	int	len;
	char	*pos;

	/* remove screen number from the display name */
	memset(disp_name, 0, sizeof(disp_name));
	strncpy(disp_name, host_name ? host_name : tty_line, sizeof(disp_name)-1);
	pos = strrchr(disp_name, ':');
	if (pos) {
		pos = strchr(pos, '.');
		if (pos)
			*pos = '\0';
	}
	sysnerr ((int)(long)(ttys = fopen (ttys_file, "r")), ttys_file);
	while ((c = getc (ttys)) != EOF)
		if (c == '\n') {
			++slot;
			column0 = 1;
		} else
			column0 = 0;
	if (!column0)
		++slot;
	(void) fclose (ttys);
	sysnerr ((int)(long)(servers = fopen (servers_file, "r")), servers_file);

	len = strlen (disp_name);
	column0 = 1;
	while (fgets (servers_line, sizeof (servers_line), servers)) {
		if (column0 && *servers_line != '#') {
			if (!strncmp (disp_name, servers_line, len) &&
			    (servers_line[len] == ' ' ||
			     servers_line[len] == '\t'))
				return slot;
			++slot;
		}
		if (servers_line[strlen(servers_line)-1] != '\n')
			column0 = 0;
		else
			column0 = 1;
	}
	/*
	 * display not found in Xservers file - allocate utmp entry dinamically
	 */
	return findslot (tty_line, host_name, addp, slot);
}

/*
 * find a free utmp slot for the X display.  This allocates a new entry
 * past the regular tty entries if necessary, reusing existing entries
 * (identified by (line,hostname)) if possible.
 */
static int
findslot (char *line_name, char *host_name, int addp, int slot)
{
	int	utmp;
	struct	utmp entry;
	int	found = 0;
	int	freeslot = -1;

	syserr(utmp = open (utmp_file, O_RDONLY), "open utmp");

	/*
	 * first, try to locate a previous entry for this display
	 * also record location of a free slots in case we need a new one
	 */
	syserr ((int) lseek (utmp, (off_t) slot * sizeof (struct utmp), 0), "lseek");

	if (!host_name)
		host_name = "";

	while (read (utmp, (char *) &entry, sizeof (entry)) == sizeof (entry)) {
		if (strncmp(entry.ut_line, line_name,
			sizeof(entry.ut_line)) == 0
#ifdef HAVE_STRUCT_UTMP_UT_HOST
		    &&
		    strncmp(entry.ut_host, host_name,
			sizeof(entry.ut_host)) == 0
#endif
		   ) {
			found = 1;
			break;
		}
		if (freeslot < 0 && *entry.ut_name == '\0')
			freeslot = slot;
		++slot;
	}

	close (utmp);

	if (found)
		return slot;
	else if (!addp)
		return 0;	/* trying to delete a non-existing entry */
	else if (freeslot < 0)
		return slot;	/* first slot past current entries */
	else
		return freeslot;
}
#endif

#ifdef HAVE_STRUCT_UTMP_UT_ID
/*
--------------------------------------------------------------------
mix -- mix 3 32-bit values reversibly.
For every delta with one or two bits set, and the deltas of all three
  high bits or all three low bits, whether the original value of a,b,c
  is almost all zero or is uniformly distributed,
* If mix() is run forward or backward, at least 32 bits in a,b,c
  have at least 1/4 probability of changing.
* If mix() is run forward, every bit of c will change between 1/3 and
  2/3 of the time.  (Well, 22/100 and 78/100 for some 2-bit deltas.)
mix() was built out of 36 single-cycle latency instructions in a
  structure that could supported 2x parallelism, like so:
      a -= b;
      a -= c; x = (c>>13);
      b -= c; a ^= x;
      b -= a; x = (a<<8);
      c -= a; b ^= x;
      c -= b; x = (b>>13);
      ...
  Unfortunately, superscalar Pentiums and Sparcs can't take advantage
  of that parallelism.  They've also turned some of those single-cycle
  latency instructions into multi-cycle latency instructions.  Still,
  this is the fastest good hash I could find.  There were about 2^^68
  to choose from.  I only looked at a billion or so.
--------------------------------------------------------------------
*/
#define mix(a,b,c) \
{ \
  a -= b; a -= c; a ^= (c>>13); \
  b -= c; b -= a; b ^= (a<<8); \
  c -= a; c -= b; c ^= (b>>13); \
  a -= b; a -= c; a ^= (c>>12);  \
  b -= c; b -= a; b ^= (a<<16); \
  c -= a; c -= b; c ^= (b>>5); \
  a -= b; a -= c; a ^= (c>>3);  \
  b -= c; b -= a; b ^= (a<<10); \
  c -= a; c -= b; c ^= (b>>15); \
}

/*
--------------------------------------------------------------------
hash() -- hash a variable-length key into a 32-bit value
  k       : the key (the unaligned variable-length array of bytes)
  len     : the length of the key, counting by bytes
  initval : can be any 4-byte value
Returns a 32-bit value.  Every bit of the key affects every bit of
the return value.  Every 1-bit and 2-bit delta achieves avalanche.
About 6*len+35 instructions.

The best hash table sizes are powers of 2.  There is no need to do
mod a prime (mod is sooo slow!).  If you need less than 32 bits,
use a bitmask.  For example, if you need only 10 bits, do
  h = (h & hashmask(10));
In which case, the hash table should have hashsize(10) elements.

If you are hashing n strings (ub1 **)k, do it like this:
  for (i=0, h=0; i<n; ++i) h = hash( k[i], len[i], h);

By Bob Jenkins, 1996.  bob_jenkins@burtleburtle.net.  You may use this
code any way you wish, private, educational, or commercial.  It's free.

[On 27 May 2004, Bob Jenkins further clarified the above statement.

  From: Bob Jenkins <bob_jenkins@burtleburtle.net>
  Date: Thu, 27 May 2004 22:33:06 -0700
  To: Margarita Manterola <marga@marga.com.ar>
  Subject: Re: Hash function

  The algorithm is public domain.  I ask that I be referenced as the
  source of the algorithm, but I can't enforce that, since being public
  domain means I've reserved no rights at all.

-- Branden Robinson, 2004-06-06]

See http://burtleburtle.net/bob/hash/evahash.html
Use for hash table lookup, or anything where one collision in 2^^32 is
acceptable.  Do NOT use for cryptographic purposes.
--------------------------------------------------------------------
*/

ub4
hash(register ub1 *k, register ub4 length, register ub4 initval)
{
   register ub4 a,b,c,len;

   /* Set up the internal state */
   len = length;
   a = b = 0x9e3779b9;  /* the golden ratio; an arbitrary value */
   c = initval;         /* the previous hash value */

   /*---------------------------------------- handle most of the key */
   while (len >= 12)
   {
      a += (k[0] +((ub4)k[1]<<8) +((ub4)k[2]<<16) +((ub4)k[3]<<24));
      b += (k[4] +((ub4)k[5]<<8) +((ub4)k[6]<<16) +((ub4)k[7]<<24));
      c += (k[8] +((ub4)k[9]<<8) +((ub4)k[10]<<16)+((ub4)k[11]<<24));
      mix(a,b,c);
      k += 12; len -= 12;
   }

   /*------------------------------------- handle the last 11 bytes */
   c += length;
   switch(len)              /* all the case statements fall through */
   {
   case 11: c+=((ub4)k[10]<<24);
   case 10: c+=((ub4)k[9]<<16);
   case 9 : c+=((ub4)k[8]<<8);
      /* the first byte of c is reserved for the length */
   case 8 : b+=((ub4)k[7]<<24);
   case 7 : b+=((ub4)k[6]<<16);
   case 6 : b+=((ub4)k[5]<<8);
   case 5 : b+=k[4];
   case 4 : a+=((ub4)k[3]<<24);
   case 3 : a+=((ub4)k[2]<<16);
   case 2 : a+=((ub4)k[1]<<8);
   case 1 : a+=k[0];
     /* case 0: nothing left to add */
   }
   mix(a,b,c);
   /*-------------------------------------------- report the result */
   return c;
}

#endif