1 /*
2 * Copyright (c) 1993 Martin Birgmeier
3 * All rights reserved.
4 *
5 * You may redistribute unmodified or modified versions of this source
6 * code provided that the above copyright notice and this and the
7 * following conditions are retained.
8 *
9 * This software is provided ``as is'', and comes with no warranties
10 * of any kind. I shall in no event be liable for anything that happens
11 * to anyone/anything when using this software.
12 */
13
14 /*
15 FUNCTION
16 <<rand48>>, <<drand48>>, <<erand48>>, <<lrand48>>, <<nrand48>>, <<mrand48>>, <<jrand48>>, <<srand48>>, <<seed48>>, <<lcong48>>---pseudo-random number generators and initialization routines
17
18 INDEX
19 rand48
20 INDEX
21 drand48
22 INDEX
23 erand48
24 INDEX
25 lrand48
26 INDEX
27 nrand48
28 INDEX
29 mrand48
30 INDEX
31 jrand48
32 INDEX
33 srand48
34 INDEX
35 seed48
36 INDEX
37 lcong48
38
39 SYNOPSIS
40 #include <stdlib.h>
41 double drand48(void);
42 double erand48(unsigned short <[xseed]>[3]);
43 long lrand48(void);
44 long nrand48(unsigned short <[xseed]>[3]);
45 long mrand48(void);
46 long jrand48(unsigned short <[xseed]>[3]);
47 void srand48(long <[seed]>);
48 unsigned short *seed48(unsigned short <[xseed]>[3]);
49 void lcong48(unsigned short <[p]>[7]);
50
51 DESCRIPTION
52 The <<rand48>> family of functions generates pseudo-random numbers
53 using a linear congruential algorithm working on integers 48 bits in size.
54 The particular formula employed is
55 r(n+1) = (a * r(n) + c) mod m
56 where the default values are
57 for the multiplicand a = 0xfdeece66d = 25214903917 and
58 the addend c = 0xb = 11. The modulo is always fixed at m = 2 ** 48.
59 r(n) is called the seed of the random number generator.
60
61 For all the six generator routines described next, the first
62 computational step is to perform a single iteration of the algorithm.
63
64 <<drand48>> and <<erand48>>
65 return values of type double. The full 48 bits of r(n+1) are
66 loaded into the mantissa of the returned value, with the exponent set
67 such that the values produced lie in the interval [0.0, 1.0].
68
69 <<lrand48>> and <<nrand48>>
70 return values of type long in the range
71 [0, 2**31-1]. The high-order (31) bits of
72 r(n+1) are loaded into the lower bits of the returned value, with
73 the topmost (sign) bit set to zero.
74
75 <<mrand48>> and <<jrand48>>
76 return values of type long in the range
77 [-2**31, 2**31-1]. The high-order (32) bits of
78 r(n+1) are loaded into the returned value.
79
80 <<drand48>>, <<lrand48>>, and <<mrand48>>
81 use an internal buffer to store r(n). For these functions
82 the initial value of r(0) = 0x1234abcd330e = 20017429951246.
83
84 On the other hand, <<erand48>>, <<nrand48>>, and <<jrand48>>
85 use a user-supplied buffer to store the seed r(n),
86 which consists of an array of 3 shorts, where the zeroth member
87 holds the least significant bits.
88
89 All functions share the same multiplicand and addend.
90
91 <<srand48>> is used to initialize the internal buffer r(n) of
92 <<drand48>>, <<lrand48>>, and <<mrand48>>
93 such that the 32 bits of the seed value are copied into the upper 32 bits
94 of r(n), with the lower 16 bits of r(n) arbitrarily being set to 0x330e.
95 Additionally, the constant multiplicand and addend of the algorithm are
96 reset to the default values given above.
97
98 <<seed48>> also initializes the internal buffer r(n) of
99 <<drand48>>, <<lrand48>>, and <<mrand48>>,
100 but here all 48 bits of the seed can be specified in an array of 3 shorts,
101 where the zeroth member specifies the lowest bits. Again,
102 the constant multiplicand and addend of the algorithm are
103 reset to the default values given above.
104 <<seed48>> returns a pointer to an array of 3 shorts which contains
105 the old seed.
106 This array is statically allocated, thus its contents are lost after
107 each new call to <<seed48>>.
108
109 Finally, <<lcong48>> allows full control over the multiplicand and
110 addend used in <<drand48>>, <<erand48>>, <<lrand48>>, <<nrand48>>,
111 <<mrand48>>, and <<jrand48>>,
112 and the seed used in <<drand48>>, <<lrand48>>, and <<mrand48>>.
113 An array of 7 shorts is passed as parameter; the first three shorts are
114 used to initialize the seed; the second three are used to initialize the
115 multiplicand; and the last short is used to initialize the addend.
116 It is thus not possible to use values greater than 0xffff as the addend.
117
118 Note that all three methods of seeding the random number generator
119 always also set the multiplicand and addend for any of the six
120 generator calls.
121
122 For a more powerful random number generator, see <<random>>.
123
124 PORTABILITY
125 SUS requires these functions.
126
127 No supporting OS subroutines are required.
128 */
129
130 #include "rand48.h"
131
132 NEWLIB_THREAD_LOCAL struct _rand48 _rand48 =
133 {
134 ._seed = { _RAND48_SEED_0, _RAND48_SEED_1, _RAND48_SEED_2 },
135 ._mult = { _RAND48_MULT_0, _RAND48_MULT_1, _RAND48_MULT_2 },
136 ._add = _RAND48_ADD,
137 };
138
139 void
__dorand48(struct _rand48 * r,unsigned short xseed[3])140 __dorand48 (struct _rand48 *r,
141 unsigned short xseed[3])
142 {
143 unsigned long accu;
144 unsigned short temp[2];
145
146 accu = (unsigned long) r->_mult[0] * (unsigned long) xseed[0] +
147 (unsigned long) r->_add;
148 temp[0] = (unsigned short) accu; /* lower 16 bits */
149 accu >>= sizeof(unsigned short) * 8;
150 accu += (unsigned long) r->_mult[0] * (unsigned long) xseed[1] +
151 (unsigned long) r->_mult[1] * (unsigned long) xseed[0];
152 temp[1] = (unsigned short) accu; /* middle 16 bits */
153 accu >>= sizeof(unsigned short) * 8;
154 accu += r->_mult[0] * xseed[2] + r->_mult[1] * xseed[1] + r->_mult[2] * xseed[0];
155 xseed[0] = temp[0];
156 xseed[1] = temp[1];
157 xseed[2] = (unsigned short) accu;
158 }
159
