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