sys/kern/subr_prng.c

   1 /*-
   2  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
   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 __FBSDID("$FreeBSD$");
  30
  31 #include <sys/param.h>
  32 #include <sys/kernel.h>
  33 #include <sys/pcpu.h>
  34 #include <sys/prng.h>
  35 #include <sys/smp.h>
  36 #include <sys/systm.h>
  37
  38 #if !PCG_HAS_128BIT_OPS
  39 /* On 32-bit platforms, gang together two 32-bit generators. */
  40 typedef struct {
  41         pcg32u_random_t states[2];
  42 } pcg64u_random_t;
  43
  44 static inline void
  45 pcg64u_srandom_r(pcg64u_random_t *state64, uint64_t seed)
  46 {
  47         pcg32u_srandom_r(&state64->states[0], seed);
  48         pcg32u_srandom_r(&state64->states[1], seed);
  49 }
  50
  51 static inline uint64_t
  52 pcg64u_random_r(pcg64u_random_t *state64)
  53 {
  54         return ((((uint64_t)pcg32u_random_r(&state64->states[0])) << 32) |
  55             pcg32u_random_r(&state64->states[1]));
  56 }
  57
  58 static inline uint64_t
  59 pcg64u_boundedrand_r(pcg64u_random_t *state64, uint64_t bound)
  60 {
  61         uint64_t threshold = -bound % bound;
  62         for (;;) {
  63                 uint64_t r = pcg64u_random_r(state64);
  64                 if (r >= threshold)
  65                         return (r % bound);
  66         }
  67 }
  68 #endif
  69
  70 DPCPU_DEFINE_STATIC(pcg32u_random_t, pcpu_prng32_state);
  71 DPCPU_DEFINE_STATIC(pcg64u_random_t, pcpu_prng64_state);
  72
  73 static void
  74 prng_init(void *dummy __unused)
  75 {
  76         pcg32u_random_t *state;
  77         pcg64u_random_t *state64;
  78         int i;
  79
  80         CPU_FOREACH(i) {
  81                 state = DPCPU_ID_PTR(i, pcpu_prng32_state);
  82                 pcg32u_srandom_r(state, 1);
  83                 state64 = DPCPU_ID_PTR(i, pcpu_prng64_state);
  84                 pcg64u_srandom_r(state64, 1);
  85         }
  86 }
  87 SYSINIT(prng_init, SI_SUB_CPU, SI_ORDER_ANY, prng_init, NULL);
  88
  89 uint32_t
  90 prng32(void)
  91 {
  92         uint32_t r;
  93
  94         critical_enter();
  95         r = pcg32u_random_r(DPCPU_PTR(pcpu_prng32_state));
  96         critical_exit();
  97         return (r);
  98 }
  99
 100 uint32_t
 101 prng32_bounded(uint32_t bound)
 102 {
 103         uint32_t r;
 104
 105         critical_enter();
 106         r = pcg32u_boundedrand_r(DPCPU_PTR(pcpu_prng32_state), bound);
 107         critical_exit();
 108         return (r);
 109 }
 110
 111 uint64_t
 112 prng64(void)
 113 {
 114         uint64_t r;
 115
 116         critical_enter();
 117         r = pcg64u_random_r(DPCPU_PTR(pcpu_prng64_state));
 118         critical_exit();
 119         return (r);
 120 }
 121
 122 uint64_t
 123 prng64_bounded(uint64_t bound)
 124 {
 125         uint64_t r;
 126
 127         critical_enter();
 128         r = pcg64u_boundedrand_r(DPCPU_PTR(pcpu_prng64_state), bound);
 129         critical_exit();
 130         return (r);
 131 }