root / prex-0.9.0 / usr / lib / libc / stdlib / random.c @ 03e9c04a
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1 | 03e9c04a | Brad Neuman | /*-
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2 | * Copyright (c) 1992, 1993
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3 | * The Regents of the University of California. All rights reserved.
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4 | *
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5 | * Redistribution and use in source and binary forms, with or without
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6 | * modification, are permitted provided that the following conditions
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7 | * are met:
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8 | * 1. Redistributions of source code must retain the above copyright
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9 | * notice, this list of conditions and the following disclaimer.
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10 | * 2. Redistributions in binary form must reproduce the above copyright
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11 | * notice, this list of conditions and the following disclaimer in the
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12 | * documentation and/or other materials provided with the distribution.
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13 | * 4. Neither the name of the University nor the names of its contributors
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14 | * may be used to endorse or promote products derived from this software
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15 | * without specific prior written permission.
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16 | *
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17 | * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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18 | * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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19 | * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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20 | * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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21 | * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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22 | * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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23 | * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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24 | * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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25 | * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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26 | * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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27 | * SUCH DAMAGE.
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28 | *
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29 | * @(#)random.c 8.1 (Berkeley) 6/10/93
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30 | */
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31 | |||
32 | #include <sys/cdefs.h> |
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33 | #include <sys/types.h> |
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34 | #include <stdlib.h> |
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35 | |||
36 | #define NSHUFF 50 /* to drop some "seed -> 1st value" linearity */ |
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37 | |||
38 | static u_long randseed = 937186357; /* after srandom(1), NSHUFF counted */ |
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39 | |||
40 | void
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41 | srandom(seed) |
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42 | u_long seed; |
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43 | { |
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44 | int i;
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45 | |||
46 | randseed = seed; |
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47 | for (i = 0; i < NSHUFF; i++) |
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48 | (void)random();
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49 | } |
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50 | |||
51 | /*
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52 | * Pseudo-random number generator for randomizing the profiling clock,
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53 | * and whatever else we might use it for. The result is uniform on
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54 | * [0, 2^31 - 1].
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55 | */
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56 | long
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57 | random() |
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58 | { |
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59 | long x, hi, lo, t;
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60 | |||
61 | /*
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62 | * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
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63 | * From "Random number generators: good ones are hard to find",
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64 | * Park and Miller, Communications of the ACM, vol. 31, no. 10,
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65 | * October 1988, p. 1195.
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66 | */
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67 | /* Can't be initialized with 0, so use another value. */
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68 | if ((x = randseed) == 0) |
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69 | x = 123459876;
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70 | hi = x / 127773;
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71 | lo = x % 127773;
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72 | t = 16807 * lo - 2836 * hi; |
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73 | if (t < 0) |
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74 | t += 0x7fffffff;
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75 | randseed = t; |
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76 | return (t);
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77 | } |