subr_prng.c

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    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 }

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FreeBSD/Linux Kernel Cross Reference sys/kern/subr_prng.c

FreeBSD/Linux Kernel Cross Reference
sys/kern/subr_prng.c