message-logging-kernels/c_randdp.c at master · KADichev/message-logging-kernels · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
/*
*/
#if defined(USE_POW)
#define r23 pow(0.5, 23.0)
#define r46 (r23*r23)
#define t23 pow(2.0, 23.0)
#define t46 (t23*t23)
#else
#define r23 (0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5*0.5)
#define r46 (r23*r23)
#define t23 (2.0*2.0*2.0*2.0*2.0*2.0*2.0*2.0*2.0*2.0*2.0*2.0*2.0*2.0*2.0*2.0*2.0*2.0*2.0*2.0*2.0*2.0*2.0)
#define t46 (t23*t23)
#endif

/*c---------------------------------------------------------------------
c---------------------------------------------------------------------*/

double randlc (double *x, double a) {

/*c---------------------------------------------------------------------
c---------------------------------------------------------------------*/

/*c---------------------------------------------------------------------
c
c   This routine returns a uniform pseudorandom double precision number in the
c   range (0, 1) by using the linear congruential generator
c
c   x_{k+1} = a x_k  (mod 2^46)
c
c   where 0 < x_k < 2^46 and 0 < a < 2^46.  This scheme generates 2^44 numbers
c   before repeating.  The argument A is the same as 'a' in the above formula,
c   and X is the same as x_0.  A and X must be odd double precision integers
c   in the range (1, 2^46).  The returned value RANDLC is normalized to be
c   between 0 and 1, i.e. RANDLC = 2^(-46) * x_1.  X is updated to contain
c   the new seed x_1, so that subsequent calls to RANDLC using the same
c   arguments will generate a continuous sequence.
c
c   This routine should produce the same results on any computer with at least
c   48 mantissa bits in double precision floating point data.  On 64 bit
c   systems, double precision should be disabled.
c
c   David H. Bailey     October 26, 1990
c
c---------------------------------------------------------------------*/

    double t1,t2,t3,t4,a1,a2,x1,x2,z;

/*c---------------------------------------------------------------------
c   Break A into two parts such that A = 2^23 * A1 + A2.
c---------------------------------------------------------------------*/
    t1 = r23 * a;
    a1 = (int)t1;
    a2 = a - t23 * a1;

/*c---------------------------------------------------------------------
c   Break X into two parts such that X = 2^23 * X1 + X2, compute
c   Z = A1 * X2 + A2 * X1  (mod 2^23), and then
c   X = 2^23 * Z + A2 * X2  (mod 2^46).
c---------------------------------------------------------------------*/
    t1 = r23 * (*x);
    x1 = (int)t1;
    x2 = (*x) - t23 * x1;
    t1 = a1 * x2 + a2 * x1;
    t2 = (int)(r23 * t1);
    z = t1 - t23 * t2;
    t3 = t23 * z + a2 * x2;
    t4 = (int)(r46 * t3);
    (*x) = t3 - t46 * t4;

    return (r46 * (*x));
}

/*c---------------------------------------------------------------------
c---------------------------------------------------------------------*/

void vranlc (int n, double *x_seed, double a, double y[]) {

/*c---------------------------------------------------------------------
c---------------------------------------------------------------------*/

/*c---------------------------------------------------------------------
c
c   This routine generates N uniform pseudorandom double precision numbers in
c   the range (0, 1) by using the linear congruential generator
c
c   x_{k+1} = a x_k  (mod 2^46)
c
c   where 0 < x_k < 2^46 and 0 < a < 2^46.  This scheme generates 2^44 numbers
c   before repeating.  The argument A is the same as 'a' in the above formula,
c   and X is the same as x_0.  A and X must be odd double precision integers
c   in the range (1, 2^46).  The N results are placed in Y and are normalized
c   to be between 0 and 1.  X is updated to contain the new seed, so that
c   subsequent calls to VRANLC using the same arguments will generate a
c   continuous sequence.  If N is zero, only initialization is performed, and
c   the variables X, A and Y are ignored.
c
c   This routine is the standard version designed for scalar or RISC systems.
c   However, it should produce the same results on any single processor
c   computer with at least 48 mantissa bits in double precision floating point
c   data.  On 64 bit systems, double precision should be disabled.
c
c---------------------------------------------------------------------*/

    int i;
    double x,t1,t2,t3,t4,a1,a2,x1,x2,z;

/*c---------------------------------------------------------------------
c   Break A into two parts such that A = 2^23 * A1 + A2.
c---------------------------------------------------------------------*/
    t1 = r23 * a;
    a1 = (int)t1;
    a2 = a - t23 * a1;
    x = *x_seed;

/*c---------------------------------------------------------------------
c   Generate N results.   This loop is not vectorizable.
c---------------------------------------------------------------------*/
    for (i = 1; i <= n; i++) {

/*c---------------------------------------------------------------------
c   Break X into two parts such that X = 2^23 * X1 + X2, compute
c   Z = A1 * X2 + A2 * X1  (mod 2^23), and then
c   X = 2^23 * Z + A2 * X2  (mod 2^46).
c---------------------------------------------------------------------*/
        t1 = r23 * x;
        x1 = (int)t1;
        x2 = x - t23 * x1;
        t1 = a1 * x2 + a2 * x1;
        t2 = (int)(r23 * t1);
        z = t1 - t23 * t2;
        t3 = t23 * z + a2 * x2;
        t4 = (int)(r46 * t3);
        x = t3 - t46 * t4;
        y[i] = r46 * x;
    }
    *x_seed = x;
}