xref: /freebsd/sys/kern/subr_prng.c (revision 5e3190f700637fcfc1a52daeaa4a031fdd2557c7)
1 /*-
2  * SPDX-License-Identifier: BSD-2-Clause
3  *
4  * Copyright 2020 Conrad Meyer <cem@FreeBSD.org>.  All rights reserved.
5  *
6  * Redistribution and use in source and binary forms, with or without
7  * modification, are permitted provided that the following conditions
8  * are met:
9  * 1. Redistributions of source code must retain the above copyright
10  *    notice, this list of conditions and the following disclaimer.
11  * 2. Redistributions in binary form must reproduce the above copyright
12  *    notice, this list of conditions and the following disclaimer in the
13  *    documentation and/or other materials provided with the distribution.
14  *
15  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
16  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
17  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
18  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
19  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
20  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
21  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
22  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
23  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
24  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
25  * SUCH DAMAGE.
26  */
27 
28 #include <sys/cdefs.h>
29 #include <sys/param.h>
30 #include <sys/kernel.h>
31 #include <sys/pcpu.h>
32 #include <sys/prng.h>
33 #include <sys/smp.h>
34 #include <sys/systm.h>
35 
36 #if !PCG_HAS_128BIT_OPS
37 /* On 32-bit platforms, gang together two 32-bit generators. */
38 typedef struct {
39 	pcg32u_random_t states[2];
40 } pcg64u_random_t;
41 
42 static inline void
43 pcg64u_srandom_r(pcg64u_random_t *state64, uint64_t seed)
44 {
45 	pcg32u_srandom_r(&state64->states[0], seed);
46 	pcg32u_srandom_r(&state64->states[1], seed);
47 }
48 
49 static inline uint64_t
50 pcg64u_random_r(pcg64u_random_t *state64)
51 {
52 	return ((((uint64_t)pcg32u_random_r(&state64->states[0])) << 32) |
53 	    pcg32u_random_r(&state64->states[1]));
54 }
55 
56 static inline uint64_t
57 pcg64u_boundedrand_r(pcg64u_random_t *state64, uint64_t bound)
58 {
59 	uint64_t threshold = -bound % bound;
60 	for (;;) {
61 		uint64_t r = pcg64u_random_r(state64);
62 		if (r >= threshold)
63 			return (r % bound);
64 	}
65 }
66 #endif
67 
68 DPCPU_DEFINE_STATIC(pcg32u_random_t, pcpu_prng32_state);
69 DPCPU_DEFINE_STATIC(pcg64u_random_t, pcpu_prng64_state);
70 
71 static void
72 prng_init(void *dummy __unused)
73 {
74 	pcg32u_random_t *state;
75 	pcg64u_random_t *state64;
76 	int i;
77 
78 	CPU_FOREACH(i) {
79 		state = DPCPU_ID_PTR(i, pcpu_prng32_state);
80 		pcg32u_srandom_r(state, 1);
81 		state64 = DPCPU_ID_PTR(i, pcpu_prng64_state);
82 		pcg64u_srandom_r(state64, 1);
83 	}
84 }
85 SYSINIT(prng_init, SI_SUB_CPU, SI_ORDER_ANY, prng_init, NULL);
86 
87 uint32_t
88 prng32(void)
89 {
90 	uint32_t r;
91 
92 	critical_enter();
93 	r = pcg32u_random_r(DPCPU_PTR(pcpu_prng32_state));
94 	critical_exit();
95 	return (r);
96 }
97 
98 uint32_t
99 prng32_bounded(uint32_t bound)
100 {
101 	uint32_t r;
102 
103 	critical_enter();
104 	r = pcg32u_boundedrand_r(DPCPU_PTR(pcpu_prng32_state), bound);
105 	critical_exit();
106 	return (r);
107 }
108 
109 uint64_t
110 prng64(void)
111 {
112 	uint64_t r;
113 
114 	critical_enter();
115 	r = pcg64u_random_r(DPCPU_PTR(pcpu_prng64_state));
116 	critical_exit();
117 	return (r);
118 }
119 
120 uint64_t
121 prng64_bounded(uint64_t bound)
122 {
123 	uint64_t r;
124 
125 	critical_enter();
126 	r = pcg64u_boundedrand_r(DPCPU_PTR(pcpu_prng64_state), bound);
127 	critical_exit();
128 	return (r);
129 }
130