1 // ============================================================================
2 // Artsoft Retro-Game Library
3 // ----------------------------------------------------------------------------
4 // (c) 1995-2014 by Artsoft Entertainment
7 // http://www.artsoft.org/
8 // ----------------------------------------------------------------------------
10 // ============================================================================
13 * Copyright (c) 1983 Regents of the University of California.
14 * All rights reserved.
16 * Redistribution and use in source and binary forms are permitted
17 * provided that the above copyright notice and this paragraph are
18 * duplicated in all such forms and that any documentation,
19 * advertising materials, and other materials related to such
20 * distribution and use acknowledge that the software was developed
21 * by the University of California, Berkeley. The name of the
22 * University may not be used to endorse or promote products derived
23 * from this software without specific prior written permission.
24 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
25 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
26 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
30 * This is derived from the Berkeley source:
31 * @(#)random.c 5.5 (Berkeley) 7/6/88
32 * It was reworked for the GNU C Library by Roland McGrath.
42 /* An improved random number generation package. In addition to the standard
43 rand()/srand() like interface, this package also has a special state info
44 interface. The initstate() routine is called with a seed, an array of
45 bytes, and a count of how many bytes are being passed in; this array is
46 then initialized to contain information for random number generation with
47 that much state information. Good sizes for the amount of state
48 information are 32, 64, 128, and 256 bytes. The state can be switched by
49 calling the setstate() function with the same array as was initiallized
50 with initstate(). By default, the package runs with 128 bytes of state
51 information and generates far better random numbers than a linear
52 congruential generator. If the amount of state information is less than
53 32 bytes, a simple linear congruential R.N.G. is used. Internally, the
54 state information is treated as an array of longs; the zeroeth element of
55 the array is the type of R.N.G. being used (small integer); the remainder
56 of the array is the state information for the R.N.G. Thus, 32 bytes of
57 state information will give 7 longs worth of state information, which will
58 allow a degree seven polynomial. (Note: The zeroeth word of state
59 information also has some other information stored in it; see setstate
60 for details). The random number generation technique is a linear feedback
61 shift register approach, employing trinomials (since there are fewer terms
62 to sum up that way). In this approach, the least significant bit of all
63 the numbers in the state table will act as a linear feedback shift register,
64 and will have period 2^deg - 1 (where deg is the degree of the polynomial
65 being used, assuming that the polynomial is irreducible and primitive).
66 The higher order bits will have longer periods, since their values are
67 also influenced by pseudo-random carries out of the lower bits. The
68 total period of the generator is approximately deg*(2**deg - 1); thus
69 doubling the amount of state information has a vast influence on the
70 period of the generator. Note: The deg*(2**deg - 1) is an approximation
71 only good for large deg, when the period of the shift register is the
72 dominant factor. With deg equal to seven, the period is actually much
73 longer than the 7*(2**7 - 1) predicted by this formula. */
77 /* For each of the currently supported random number generators, we have a
78 break value on the amount of state information (you need at least thi
79 bytes of state info to support this random number generator), a degree for
80 the polynomial (actually a trinomial) that the R.N.G. is based on, and
81 separation between the two lower order coefficients of the trinomial. */
83 /* Linear congruential. */
89 /* x**7 + x**3 + 1. */
101 /* x**31 + x**3 + 1. */
114 /* Array versions of the above information to make code run faster.
115 Relies on fact that TYPE_i == i. */
117 #define MAX_TYPES 5 /* Max number of types above. */
121 /* Initially, everything is set up as if from:
122 initstate(1, randtbl, 128);
123 Note that this initialization takes advantage of the fact that srandom
124 advances the front and rear pointers 10*rand_deg times, and hence the
125 rear pointer which starts at 0 will also end up at zero; thus the zeroeth
126 element of the state information, which contains info about the current
127 position of the rear pointer is just
128 (MAX_TYPES * (rptr - state)) + TYPE_3 == TYPE_3. */
130 static int randtbl_0[DEG_3 + 1] =
133 -851904987, -43806228, -2029755270, 1390239686, -1912102820,
134 -485608943, 1969813258, -1590463333, -1944053249, 455935928, 508023712,
135 -1714531963, 1800685987, -2015299881, 654595283, -1149023258,
136 -1470005550, -1143256056, -1325577603, -1568001885, 1275120390,
137 -607508183, -205999574, -1696891592, 1492211999, -1528267240,
138 -952028296, -189082757, 362343714, 1424981831, 2039449641,
140 static int randtbl_1[DEG_3 + 1] =
143 -851904987, -43806228, -2029755270, 1390239686, -1912102820,
144 -485608943, 1969813258, -1590463333, -1944053249, 455935928, 508023712,
145 -1714531963, 1800685987, -2015299881, 654595283, -1149023258,
146 -1470005550, -1143256056, -1325577603, -1568001885, 1275120390,
147 -607508183, -205999574, -1696891592, 1492211999, -1528267240,
148 -952028296, -189082757, 362343714, 1424981831, 2039449641,
152 /* FPTR and RPTR are two pointers into the state info, a front and a rear
153 pointer. These two pointers are always rand_sep places aparts, as they
154 cycle through the state information. (Yes, this does mean we could get
155 away with just one pointer, but the code for random is more efficient
156 this way). The pointers are left positioned as they would be from the call:
157 initstate(1, randtbl, 128);
158 (The position of the rear pointer, rptr, is really 0 (as explained above
159 in the initialization of randtbl) because the state table pointer is set
160 to point to randtbl[1] (as explained below).) */
162 static int *fptr[2] = { &randtbl_0[SEP_3 + 1], &randtbl_1[SEP_3 + 1] };
163 static int *rptr[2] = { &randtbl_0[1], &randtbl_1[1] };
167 /* The following things are the pointer to the state information table,
168 the type of the current generator, the degree of the current polynomial
169 being used, and the separation between the two pointers.
170 Note that for efficiency of random, we remember the first location of
171 the state information, not the zeroeth. Hence it is valid to access
172 state[-1], which is used to store the type of the R.N.G.
173 Also, we remember the last location, since this is more efficient than
174 indexing every time to find the address of the last element to see if
175 the front and rear pointers have wrapped. */
177 static int *state[2] = { &randtbl_0[1], &randtbl_1[1] };
179 static int rand_type[2] = { TYPE_3, TYPE_3 };
180 static int rand_deg[2] = { DEG_3, DEG_3 };
181 static int rand_sep[2] = { SEP_3, SEP_3 };
183 static int *end_ptr[2] =
185 &randtbl_0[sizeof(randtbl_0) / sizeof(randtbl_0[0])],
186 &randtbl_1[sizeof(randtbl_1) / sizeof(randtbl_1[0])]
189 /* Initialize the random number generator based on the given seed. If the
190 type is the trivial no-state-information type, just remember the seed.
191 Otherwise, initializes state[] based on the given "seed" via a linear
192 congruential generator. Then, the pointers are set to known locations
193 that are exactly rand_sep places apart. Lastly, it cycles the state
194 information a given number of times to get rid of any initial dependencies
195 introduced by the L.C.R.N.G. Note that the initialization of randtbl[]
196 for default usage relies on values produced by this routine. */
198 void srandom_linux_libc(int nr, unsigned int x)
202 if (rand_type[nr] != TYPE_0)
206 for (i = 1; i < rand_deg[nr]; ++i)
207 state[nr][i] = (1103515145 * state[nr][i - 1]) + 12345;
209 fptr[nr] = &state[nr][rand_sep[nr]];
210 rptr[nr] = &state[nr][0];
212 for (i = 0; i < 10 * rand_deg[nr]; ++i)
213 random_linux_libc(nr);
217 /* If we are using the trivial TYPE_0 R.N.G., just do the old linear
218 congruential bit. Otherwise, we do our fancy trinomial stuff, which is the
219 same in all ther other cases due to all the global variables that have been
220 set up. The basic operation is to add the number at the rear pointer into
221 the one at the front pointer. Then both pointers are advanced to the next
222 location cyclically in the table. The value returned is the sum generated,
223 reduced to 31 bits by throwing away the "least random" low bit.
224 Note: The code takes advantage of the fact that both the front and
225 rear pointers can't wrap on the same call by not testing the rear
226 pointer if the front one has wrapped. Returns a 31-bit random number. */
228 int random_linux_libc(int nr)
230 if (rand_type[nr] == TYPE_0)
232 state[nr][0] = ((state[nr][0] * 1103515245) + 12345) & INT_MAX;
239 *fptr[nr] += *rptr[nr];
241 /* Chucking least random bit. */
242 i = (*fptr[nr] >> 1) & INT_MAX;
245 if (fptr[nr] >= end_ptr[nr])
247 fptr[nr] = state[nr];
253 if (rptr[nr] >= end_ptr[nr])
254 rptr[nr] = state[nr];