# source:trunk/sys/libupc/upc_c_randdp.c@346

Last change on this file since 346 was 1, checked in by alain, 6 years ago

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1#if defined(USE_POW)
2#define r23 pow(0.5, 23.0)
3#define r46 (r23*r23)
4#define t23 pow(2.0, 23.0)
5#define t46 (t23*t23)
6#else
7#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)
8#define r46 (r23*r23)
9#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)
10#define t46 (t23*t23)
11#endif
12
13double randlc (double *x, double a) {
14
15/*  This routine returns a uniform pseudorandom double precision number in the
16   range (0, 1) by using the linear congruential generator
17
18   x_{k+1} = a x_k  (mod 2^46)
19
20   where 0 < x_k < 2^46 and 0 < a < 2^46.  This scheme generates 2^44 numbers
21   before repeating.  The argument A is the same as 'a' in the above formula,
22   and X is the same as x_0.  A and X must be odd double precision integers
23   in the range (1, 2^46).  The returned value RANDLC is normalized to be
24   between 0 and 1, i.e. RANDLC = 2^(-46) * x_1.  X is updated to contain
25   the new seed x_1, so that subsequent calls to RANDLC using the same
26   arguments will generate a continuous sequence.
27
28   This routine should produce the same results on any computer with at least
29   48 mantissa bits in double precision floating point data.  On 64 bit
30   systems, double precision should be disabled.
31
32   David H. Bailey     October 26, 1990
33*/
34    double t1,t2,t3,t4,a1,a2,x1,x2,z;
35
36/*  Break A into two parts such that A = 2^23 * A1 + A2. */
37    t1 = r23 * a;
38    a1 = (int)t1;
39    a2 = a - t23 * a1;
40
41/*  Break X into two parts such that X = 2^23 * X1 + X2, compute
42    Z = A1 * X2 + A2 * X1  (mod 2^23), and then
43    X = 2^23 * Z + A2 * X2  (mod 2^46).  */
44    t1 = r23 * (*x);
45    x1 = (int)t1;
46    x2 = (*x) - t23 * x1;
47    t1 = a1 * x2 + a2 * x1;
48    t2 = (int)(r23 * t1);
49    z = t1 - t23 * t2;
50    t3 = t23 * z + a2 * x2;
51    t4 = (int)(r46 * t3);
52    (*x) = t3 - t46 * t4;
53
54    return (r46 * (*x));
55}
56
57void vranlc (int n, double *x_seed, double a, double y[]) {
58/* This routine generates N uniform pseudorandom double precision numbers in
59   the range (0, 1) by using the linear congruential generator
60
61   x_{k+1} = a x_k  (mod 2^46)
62
63   where 0 < x_k < 2^46 and 0 < a < 2^46.  This scheme generates 2^44 numbers
64   before repeating.  The argument A is the same as 'a' in the above formula,
65   and X is the same as x_0.  A and X must be odd double precision integers
66   in the range (1, 2^46).  The N results are placed in Y and are normalized
67   to be between 0 and 1.  X is updated to contain the new seed, so that
68   subsequent calls to VRANLC using the same arguments will generate a
69   continuous sequence.  If N is zero, only initialization is performed, and
70   the variables X, A and Y are ignored.
71
72   This routine is the standard version designed for scalar or RISC systems.
73   However, it should produce the same results on any single processor
74   computer with at least 48 mantissa bits in double precision floating point
75   data.  On 64 bit systems, double precision should be disabled.  */
76
77    int i;
78    double x,t1,t2,t3,t4,a1,a2,x1,x2,z;
79
80/* Break A into two parts such that A = 2^23 * A1 + A2.  */
81    t1 = r23 * a;
82    a1 = (int)t1;
83    a2 = a - t23 * a1;
84    x = *x_seed;
85
86/* Generate N results.   This loop is not vectorizable. */
87    for (i = 1; i <= n; i++) {
88
89/* Break X into two parts such that X = 2^23 * X1 + X2, compute
90   Z = A1 * X2 + A2 * X1  (mod 2^23), and then
91   X = 2^23 * Z + A2 * X2  (mod 2^46).  */
92        t1 = r23 * x;
93        x1 = (int)t1;
94        x2 = x - t23 * x1;
95        t1 = a1 * x2 + a2 * x1;
96        t2 = (int)(r23 * t1);
97        z = t1 - t23 * t2;
98        t3 = t23 * z + a2 * x2;
99        t4 = (int)(r46 * t3);
100        x = t3 - t46 * t4;
101        y[i] = r46 * x;
102    }
103    *x_seed = x;
104}
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