sys/kern/subr_prng.c

   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 }