Diffstat (limited to 'noncore/games/sfcave/random.cpp') (more/less context) (show whitespace changes)
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diff --git a/noncore/games/sfcave/random.cpp b/noncore/games/sfcave/random.cpp new file mode 100644 index 0000000..c4c10bb --- a/dev/null +++ b/noncore/games/sfcave/random.cpp | |||
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1 | /* ------------------------------------------------------------------------- | ||
2 | * This is an ANSI C library for multi-stream random number generation. | ||
3 | * The use of this library is recommended as a replacement for the ANSI C | ||
4 | * rand() and srand() functions, particularly in simulation applications | ||
5 | * where the statistical 'goodness' of the random number generator is | ||
6 | * important. The library supplies 256 streams of random numbers; use | ||
7 | * SelectStream(s) to switch between streams indexed s = 0,1,...,255. | ||
8 | * | ||
9 | * The streams must be initialized. The recommended way to do this is by | ||
10 | * using the function PlantSeeds(x) with the value of x used to initialize | ||
11 | * the default stream and all other streams initialized automatically with | ||
12 | * values dependent on the value of x. The following convention is used | ||
13 | * to initialize the default stream: | ||
14 | * if x > 0 then x is the state | ||
15 | * if x < 0 then the state is obtained from the system clock | ||
16 | * if x = 0 then the state is to be supplied interactively. | ||
17 | * | ||
18 | * The generator used in this library is a so-called 'Lehmer random number | ||
19 | * generator' which returns a pseudo-random number uniformly distributed | ||
20 | * 0.0 and 1.0. The period is (m - 1) where m = 2,147,483,647 and the | ||
21 | * smallest and largest possible values are (1 / m) and 1 - (1 / m) | ||
22 | * respectively. For more details see: | ||
23 | * | ||
24 | * "Random Number Generators: Good Ones Are Hard To Find" | ||
25 | * Steve Park and Keith Miller | ||
26 | * Communications of the ACM, October 1988 | ||
27 | * | ||
28 | * Name : rngs.c (Random Number Generation - Multiple Streams) | ||
29 | * Authors : Steve Park & Dave Geyer | ||
30 | * Language : ANSI C | ||
31 | * Latest Revision : 09-22-98 | ||
32 | * ------------------------------------------------------------------------- | ||
33 | */ | ||
34 | |||
35 | #include <stdio.h> | ||
36 | #include <time.h> | ||
37 | #include "random.h" | ||
38 | |||
39 | #define MODULUS 2147483647 /* DON'T CHANGE THIS VALUE */ | ||
40 | #define MULTIPLIER 48271 /* DON'T CHANGE THIS VALUE */ | ||
41 | #define CHECK 399268537 /* DON'T CHANGE THIS VALUE */ | ||
42 | #define STREAMS 256 /* # of streams, DON'T CHANGE THIS VALUE */ | ||
43 | #define A256 22925 /* jump multiplier, DON'T CHANGE THIS VALUE */ | ||
44 | #define DEFAULT 123456789 /* initial seed, use 0 < DEFAULT < MODULUS */ | ||
45 | |||
46 | static long seed[STREAMS] = {DEFAULT}; /* current state of each stream */ | ||
47 | static int stream = 0; /* stream index, 0 is the default */ | ||
48 | static int initialized = 0; /* test for stream initialization */ | ||
49 | |||
50 | |||
51 | double Random(void) | ||
52 | /* ---------------------------------------------------------------- | ||
53 | * Random returns a pseudo-random real number uniformly distributed | ||
54 | * between 0.0 and 1.0. | ||
55 | * ---------------------------------------------------------------- | ||
56 | */ | ||
57 | { | ||
58 | const long Q = MODULUS / MULTIPLIER; | ||
59 | const long R = MODULUS % MULTIPLIER; | ||
60 | long t; | ||
61 | |||
62 | t = MULTIPLIER * (seed[stream] % Q) - R * (seed[stream] / Q); | ||
63 | if (t > 0) | ||
64 | seed[stream] = t; | ||
65 | else | ||
66 | seed[stream] = t + MODULUS; | ||
67 | return ((double) seed[stream] / MODULUS); | ||
68 | } | ||
69 | |||
70 | |||
71 | void PlantSeeds(long x) | ||
72 | /* --------------------------------------------------------------------- | ||
73 | * Use this function to set the state of all the random number generator | ||
74 | * streams by "planting" a sequence of states (seeds), one per stream, | ||
75 | * with all states dictated by the state of the default stream. | ||
76 | * The sequence of planted states is separated one from the next by | ||
77 | * 8,367,782 calls to Random(). | ||
78 | * --------------------------------------------------------------------- | ||
79 | */ | ||
80 | { | ||
81 | const long Q = MODULUS / A256; | ||
82 | const long R = MODULUS % A256; | ||
83 | int j; | ||
84 | int s; | ||
85 | |||
86 | initialized = 1; | ||
87 | s = stream; /* remember the current stream */ | ||
88 | SelectStream(0); /* change to stream 0 */ | ||
89 | PutSeed(x); /* set seed[0] */ | ||
90 | stream = s; /* reset the current stream */ | ||
91 | for (j = 1; j < STREAMS; j++) { | ||
92 | x = A256 * (seed[j - 1] % Q) - R * (seed[j - 1] / Q); | ||
93 | if (x > 0) | ||
94 | seed[j] = x; | ||
95 | else | ||
96 | seed[j] = x + MODULUS; | ||
97 | } | ||
98 | } | ||
99 | |||
100 | |||
101 | void PutSeed(long x) | ||
102 | /* --------------------------------------------------------------- | ||
103 | * Use this function to set the state of the current random number | ||
104 | * generator stream according to the following conventions: | ||
105 | * if x > 0 then x is the state (unless too large) | ||
106 | * if x < 0 then the state is obtained from the system clock | ||
107 | * if x = 0 then the state is to be supplied interactively | ||
108 | * --------------------------------------------------------------- | ||
109 | */ | ||
110 | { | ||
111 | char ok = 0; | ||
112 | |||
113 | if (x > 0) | ||
114 | x = x % MODULUS; /* correct if x is too large */ | ||
115 | if (x < 0) | ||
116 | x = ((unsigned long) time((time_t *) NULL)) % MODULUS; | ||
117 | if (x == 0) | ||
118 | while (!ok) { | ||
119 | printf("\nEnter a positive integer seed (9 digits or less) >> "); | ||
120 | scanf("%ld", &x); | ||
121 | ok = (0 < x) && (x < MODULUS); | ||
122 | if (!ok) | ||
123 | printf("\nInput out of range ... try again\n"); | ||
124 | } | ||
125 | seed[stream] = x; | ||
126 | } | ||
127 | |||
128 | |||
129 | void GetSeed(long *x) | ||
130 | /* --------------------------------------------------------------- | ||
131 | * Use this function to get the state of the current random number | ||
132 | * generator stream. | ||
133 | * --------------------------------------------------------------- | ||
134 | */ | ||
135 | { | ||
136 | *x = seed[stream]; | ||
137 | } | ||
138 | |||
139 | |||
140 | void SelectStream(int index) | ||
141 | /* ------------------------------------------------------------------ | ||
142 | * Use this function to set the current random number generator | ||
143 | * stream -- that stream from which the next random number will come. | ||
144 | * ------------------------------------------------------------------ | ||
145 | */ | ||
146 | { | ||
147 | stream = ((unsigned int) index) % STREAMS; | ||
148 | if ((initialized == 0) && (stream != 0)) /* protect against */ | ||
149 | PlantSeeds(DEFAULT); /* un-initialized streams */ | ||
150 | } | ||
151 | |||
152 | |||
153 | void TestRandom(void) | ||
154 | /* ------------------------------------------------------------------ | ||
155 | * Use this (optional) function to test for a correct implementation. | ||
156 | * ------------------------------------------------------------------ | ||
157 | */ | ||
158 | { | ||
159 | long i; | ||
160 | long x; | ||
161 | double u; | ||
162 | char ok = 0; | ||
163 | |||
164 | SelectStream(0); /* select the default stream */ | ||
165 | PutSeed(1); /* and set the state to 1 */ | ||
166 | for(i = 0; i < 10000; i++) | ||
167 | u = Random(); | ||
168 | GetSeed(&x); /* get the new state value */ | ||
169 | ok = (x == CHECK); /* and check for correctness */ | ||
170 | |||
171 | SelectStream(1); /* select stream 1 */ | ||
172 | PlantSeeds(1); /* set the state of all streams */ | ||
173 | GetSeed(&x); /* get the state of stream 1 */ | ||
174 | ok = ok && (x == A256); /* x should be the jump multiplier */ | ||
175 | if (ok) | ||
176 | printf("\n The implementation of rngs.c is correct.\n\n"); | ||
177 | else | ||
178 | printf("\n\a ERROR -- the implementation of rngs.c is not correct.\n\n"); | ||
179 | } | ||