Line data    Source code

       1             : /*      $OpenBSD: random.c,v 1.10 2017/09/08 05:36:53 deraadt Exp $     */
       2             : /*      $NetBSD: random.c,v 1.2 1994/10/26 06:42:42 cgd Exp $   */
       3             : 
       4             : /*-
       5             :  * Copyright (c) 1992, 1993
       6             :  *      The Regents of the University of California.  All rights reserved.
       7             :  *
       8             :  * Redistribution and use in source and binary forms, with or without
       9             :  * modification, are permitted provided that the following conditions
      10             :  * are met:
      11             :  * 1. Redistributions of source code must retain the above copyright
      12             :  *    notice, this list of conditions and the following disclaimer.
      13             :  * 2. Redistributions in binary form must reproduce the above copyright
      14             :  *    notice, this list of conditions and the following disclaimer in the
      15             :  *    documentation and/or other materials provided with the distribution.
      16             :  * 3. Neither the name of the University nor the names of its contributors
      17             :  *    may be used to endorse or promote products derived from this software
      18             :  *    without specific prior written permission.
      19             :  *
      20             :  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
      21             :  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
      22             :  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
      23             :  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
      24             :  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
      25             :  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
      26             :  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
      27             :  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
      28             :  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
      29             :  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
      30             :  * SUCH DAMAGE.
      31             :  *
      32             :  *      @(#)random.c    8.1 (Berkeley) 6/10/93
      33             :  */
      34             : 
      35             : #include <sys/param.h>
      36             : 
      37             : #include <lib/libkern/libkern.h>
      38             : 
      39             : /*
      40             :  * Pseudo-random number generator for randomizing the profiling clock.
      41             :  * The result is uniform on [0, 2^31 - 1].
      42             :  */
      43             : 
      44             : u_int32_t
      45           0 : random(void)
      46             : {
      47           0 :         struct cpu_info *ci = curcpu();
      48             :         int32_t x, hi, lo, t;
      49             : 
      50             :         /*
      51             :          * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
      52             :          * From "Random number generators: good ones are hard to find",
      53             :          * Park and Miller, Communications of the ACM, vol. 31, no. 10,
      54             :          * October 1988, p. 1195.
      55             :          */
      56           0 :         x = ci->ci_randseed;
      57           0 :         hi = x / 127773;
      58           0 :         lo = x % 127773;
      59           0 :         t = 16807 * lo - 2836 * hi;
      60           0 :         if (t <= 0)
      61           0 :                 t += 0x7fffffff;
      62           0 :         ci->ci_randseed = t;
      63           0 :         return (t);
      64             : }