[libdispatch-dev] libdispatch compiles under Linux but arc4random(3) is missing

[Mark Heily]

Good news: libdispatch now compiles successfully under Linux using libkqueue 
r96 or higher.

The test programs in the testing/ directory fail to link because 
arc4random(3) is not available on Linux. I found a compatibility function 
written for BIND that might work; the URI is:

http://mirror.its.uidaho.edu/pub/netbsd/NetBSD-current/src/external/bsd/bind/dist/lib/isc/random.c

See below for the actual code. Any objections to adding something like this 
to libdispatch?

Regards,

  - Mark


/*	$NetBSD: random.c,v 1.1.1.1 2009/03/22 15:02:07 christos Exp $	*/

/*
  * Copyright (C) 2004, 2005, 2007  Internet Systems Consortium, Inc. ("ISC")
  * Copyright (C) 1999-2003  Internet Software Consortium.
  *
  * Permission to use, copy, modify, and/or distribute this software for any
  * purpose with or without fee is hereby granted, provided that the above
  * copyright notice and this permission notice appear in all copies.
  *
  * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
  * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
  * AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
  * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
  * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
  * OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
  * PERFORMANCE OF THIS SOFTWARE.
  */

/* Id: random.c,v 1.25 2007/06/19 23:47:17 tbox Exp */

/*! \file */

#include <config.h>

#include <stdlib.h>
#include <time.h>		/* Required for time(). */
#ifdef HAVE_SYS_TYPES_H
#include <sys/types.h>
#endif
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif

#include <isc/mutex.h>
#include <isc/once.h>
#include <isc/random.h>
#include <isc/string.h>
#include <isc/util.h>

static isc_once_t once = ISC_ONCE_INIT;

static void
initialize_rand(void)
{
#ifndef HAVE_ARC4RANDOM
	unsigned int pid = getpid();
	
	/*
	 * The low bits of pid generally change faster.
	 * Xor them with the high bits of time which change slowly.
	 */
	pid = ((pid << 16) & 0xffff0000) | ((pid >> 16) & 0xffff);

	srand(time(NULL) ^ pid);
#endif
}

static void
initialize(void)
{
	RUNTIME_CHECK(isc_once_do(&once, initialize_rand) == ISC_R_SUCCESS);
}

void
isc_random_seed(isc_uint32_t seed)
{
	initialize();

#ifndef HAVE_ARC4RANDOM
	srand(seed);
#else
	arc4random_addrandom((u_char *) &seed, sizeof(isc_uint32_t));
#endif
}

void
isc_random_get(isc_uint32_t *val)
{
	REQUIRE(val != NULL);

	initialize();

#ifndef HAVE_ARC4RANDOM
	/*
	 * rand()'s lower bits are not random.
	 * rand()'s upper bit is zero.
	 */
	*val = ((rand() >> 4) & 0xffff) | ((rand() << 12) & 0xffff0000);
#else
	*val = arc4random();
#endif
}

isc_uint32_t
isc_random_jitter(isc_uint32_t max, isc_uint32_t jitter) {
	REQUIRE(jitter < max);
	if (jitter == 0)
		return (max);
	else
#ifndef HAVE_ARC4RANDOM
		return (max - rand() % jitter);
#else
		return (max - arc4random() % jitter);
#endif
}