summaryrefslogtreecommitdiff
path: root/sys/lib/libkern/arch/sh5/random.S
blob: 1a2ca5a6d37d7673b14d3877d1de1895a09bf326 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
/*	$NetBSD: random.S,v 1.1 2002/10/17 11:53:33 scw Exp $	*/

/*
 * Copyright 2002 Wasabi Systems, Inc.
 * All rights reserved.
 *
 * Written by Steve C. Woodford for Wasabi Systems, Inc.
 *
 * 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.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed for the NetBSD Project by
 *      Wasabi Systems, Inc.
 * 4. The name of Wasabi Systems, Inc. may not be used to endorse
 *    or promote products derived from this software without specific prior
 *    written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY WASABI SYSTEMS, INC. ``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 WASABI SYSTEMS, INC
 * 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.
 */
/*
 * Copyright (c) 1990,1993 The Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that: (1) source code distributions
 * retain the above copyright notice and this paragraph in its entirety, (2)
 * distributions including binary code include the above copyright notice and
 * this paragraph in its entirety in the documentation or other materials
 * provided with the distribution, and (3) all advertising materials mentioning
 * features or use of this software display the following acknowledgement:
 * ``This product includes software developed by the University of California,
 * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
 * the University nor the names of its contributors may be used to endorse
 * or promote products derived from this software without specific prior
 * written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 *
 * Here is a very good random number generator.  This implementation is
 * based on ``Two Fast Implementations of the "Minimal Standard" Random
 * Number Generator'', David G. Carta, Communications of the ACM, Jan 1990,
 * Vol 33 No 1.  Do NOT modify this code unless you have a very thorough
 * understanding of the algorithm.  It's trickier than you think.  If
 * you do change it, make sure that its 10,000'th invocation returns
 * 1043618065.
 *
 * Here is easier-to-decipher pseudocode:
 *
 * p = (16807*seed)
 * if (p < 2^31)
 * 	seed = p
 * else
 *	seed = (p & (2^31 - 1)) + 1
 * return (seed);
 *
 * The result is in (0,2^31), e.g., it's always positive.
 */

#include <machine/asm.h>

	.data
	.balign	4
ASLOCAL(randseed)
	.long	0

ENTRY(random)
	ptabs/u	r18, tr0
	LEA(_ASM_LABEL(randseed), r0)
	ld.l	r0, 0, r2
	getcon	ctc, r3			/* First time through, seed is CTC */
	cmveq	r2, r3, r2
	movi	16807, r1
	muls.l	r2, r1, r2
	shlri	r2, 31, r1		/* Isolate bits 31-63 */
	shlli	r1, 31, r1
	cmpgtu	r1, r63, r3		/* r3 = 1, if any bits 31-63 are set */
	andc	r2, r1, r2		/* Clear bits 31-63 */
	add	r2, r3, r2		/* +1, if they really were set */
	st.l	r0, 0, r2		/* Update seed */
	blink	tr0, r63