xref: /illumos-gate/usr/src/lib/libc/port/gen/rand.c (revision 1da57d55)
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5*7257d1b4Sraf  * Common Development and Distribution License (the "License").
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77c478bd9Sstevel@tonic-gate  *
87c478bd9Sstevel@tonic-gate  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
97c478bd9Sstevel@tonic-gate  * or http://www.opensolaris.org/os/licensing.
107c478bd9Sstevel@tonic-gate  * See the License for the specific language governing permissions
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137c478bd9Sstevel@tonic-gate  * When distributing Covered Code, include this CDDL HEADER in each
147c478bd9Sstevel@tonic-gate  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
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207c478bd9Sstevel@tonic-gate  */
21*7257d1b4Sraf 
227c478bd9Sstevel@tonic-gate /*
23*7257d1b4Sraf  * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
247c478bd9Sstevel@tonic-gate  * Use is subject to license terms.
257c478bd9Sstevel@tonic-gate  */
267c478bd9Sstevel@tonic-gate 
277c478bd9Sstevel@tonic-gate /*	Copyright (c) 1988 AT&T	*/
287c478bd9Sstevel@tonic-gate /*	  All Rights Reserved  	*/
297c478bd9Sstevel@tonic-gate 
307c478bd9Sstevel@tonic-gate /*
317c478bd9Sstevel@tonic-gate  * University Copyright- Copyright (c) 1982, 1986, 1988
327c478bd9Sstevel@tonic-gate  * The Regents of the University of California
337c478bd9Sstevel@tonic-gate  * All Rights Reserved
347c478bd9Sstevel@tonic-gate  *
357c478bd9Sstevel@tonic-gate  * University Acknowledgment- Portions of this document are derived from
367c478bd9Sstevel@tonic-gate  * software developed by the University of California, Berkeley, and its
377c478bd9Sstevel@tonic-gate  * contributors.
387c478bd9Sstevel@tonic-gate  */
397c478bd9Sstevel@tonic-gate 
40*7257d1b4Sraf #include "lint.h"
417c478bd9Sstevel@tonic-gate #include "thr_uberdata.h"
427c478bd9Sstevel@tonic-gate #include <stdlib.h>
437c478bd9Sstevel@tonic-gate #include <atomic.h>
447c478bd9Sstevel@tonic-gate 
457c478bd9Sstevel@tonic-gate /*
467c478bd9Sstevel@tonic-gate  * We need atomic_cas_uint() protection because a multithreaded process
477c478bd9Sstevel@tonic-gate  * may be calling rand() from different threads and because multiple
487c478bd9Sstevel@tonic-gate  * threads may be calling rand_r() using a pointer to the same seed.
497c478bd9Sstevel@tonic-gate  */
507c478bd9Sstevel@tonic-gate 
517c478bd9Sstevel@tonic-gate static uint_t rand_seed = 1;
527c478bd9Sstevel@tonic-gate 
537c478bd9Sstevel@tonic-gate #define	NEXT_SEED(s)	((s) * 1103515245 + 12345)
547c478bd9Sstevel@tonic-gate #define	NEXT_VALUE(s)	(((s) >> 16) & 0x7fff)
557c478bd9Sstevel@tonic-gate 
567c478bd9Sstevel@tonic-gate static int
rand_mt(uint_t * seed)577c478bd9Sstevel@tonic-gate rand_mt(uint_t *seed)
587c478bd9Sstevel@tonic-gate {
597c478bd9Sstevel@tonic-gate 	uint_t old_seed;
607c478bd9Sstevel@tonic-gate 	uint_t new_seed;
617c478bd9Sstevel@tonic-gate 
627c478bd9Sstevel@tonic-gate 	for (;;) {
637c478bd9Sstevel@tonic-gate 		/* force reload on every iteration */
647c478bd9Sstevel@tonic-gate 		old_seed = *(volatile uint_t *)seed;
657c478bd9Sstevel@tonic-gate 		new_seed = NEXT_SEED(old_seed);
667c478bd9Sstevel@tonic-gate 		if (atomic_cas_uint(seed, old_seed, new_seed) == old_seed)
677c478bd9Sstevel@tonic-gate 			return (NEXT_VALUE(new_seed));
687c478bd9Sstevel@tonic-gate 		SMT_PAUSE();
697c478bd9Sstevel@tonic-gate 	}
707c478bd9Sstevel@tonic-gate }
717c478bd9Sstevel@tonic-gate 
727c478bd9Sstevel@tonic-gate int
rand_r(uint_t * seed)737c478bd9Sstevel@tonic-gate rand_r(uint_t *seed)
747c478bd9Sstevel@tonic-gate {
757c478bd9Sstevel@tonic-gate 	if (curthread->ul_uberdata->uberflags.uf_mt)
767c478bd9Sstevel@tonic-gate 		return (rand_mt(seed));
777c478bd9Sstevel@tonic-gate 	return (NEXT_VALUE(*seed = NEXT_SEED(*seed)));
787c478bd9Sstevel@tonic-gate }
797c478bd9Sstevel@tonic-gate 
807c478bd9Sstevel@tonic-gate void
srand(uint_t seed)817c478bd9Sstevel@tonic-gate srand(uint_t seed)
827c478bd9Sstevel@tonic-gate {
837c478bd9Sstevel@tonic-gate 	rand_seed = seed;
847c478bd9Sstevel@tonic-gate }
857c478bd9Sstevel@tonic-gate 
867c478bd9Sstevel@tonic-gate int
rand(void)877c478bd9Sstevel@tonic-gate rand(void)
887c478bd9Sstevel@tonic-gate {
897c478bd9Sstevel@tonic-gate 	return (rand_r(&rand_seed));
907c478bd9Sstevel@tonic-gate }
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