[20] | 1 | // file: ranlux.xpp
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| 2 | #include "ranlux.h"
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| 3 | #include <stdlib.h>
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| 4 | #include <stdio.h>
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| 5 |
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| 6 | /* This is a lagged fibonacci generator with skipping developed by Luescher.
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| 7 | The sequence is a series of 24-bit integers, x_n,
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| 8 |
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| 9 | x_n = d_n + b_n
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| 10 |
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| 11 | where d_n = x_{n-10} - x_{n-24} - c_{n-1}, b_n = 0 if d_n >= 0 and
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| 12 | b_n = 2^24 if d_n < 0, c_n = 0 if d_n >= 0 and c_n = 1 if d_n < 0,
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| 13 | where after 24 samples a group of p integers are "skipped", to
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| 14 | reduce correlations. By default p = 199, but can be increased to
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| 15 | 365.
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| 16 |
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| 17 | The period of the generator is around 10^171.
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| 18 |
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| 19 | From: M. Luescher, "A portable high-quality random number generator
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| 20 | for lattice field theory calculations", Computer Physics
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| 21 | Communications, 79 (1994) 100-110.
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| 22 |
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| 23 | Available on the net as hep-lat/9309020 at http://xxx.lanl.gov/
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| 24 |
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| 25 | See also,
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| 26 |
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| 27 | F. James, "RANLUX: A Fortran implementation of the high-quality
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| 28 | pseudo-random number generator of Luscher", Computer Physics
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| 29 | Communications, 79 (1994) 111-114
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| 30 |
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| 31 | Kenneth G. Hamilton, F. James, "Acceleration of RANLUX", Computer
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| 32 | Physics Communications, 101 (1997) 241-248
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| 33 |
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| 34 | Kenneth G. Hamilton, "Assembler RANLUX for PCs", Computer Physics
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| 35 | Communications, 101 (1997) 249-253 */
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| 36 |
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| 37 | namespace siscone{
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| 38 |
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| 39 | static const unsigned long int mask_lo = 0x00ffffffUL; // 2^24 - 1
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| 40 | static const unsigned long int mask_hi = ~0x00ffffffUL;
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| 41 | static const unsigned long int two24 = 16777216; // 2^24
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| 42 |
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| 43 |
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| 44 | // internal generator structure
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| 45 | //------------------------------
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| 46 | typedef struct {
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| 47 | unsigned int i;
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| 48 | unsigned int j;
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| 49 | unsigned int n;
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| 50 | unsigned int skip;
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| 51 | unsigned int carry;
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| 52 | unsigned long int u[24];
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| 53 | } ranlux_state_t;
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| 54 |
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| 55 |
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| 56 | // internal generator state
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| 57 | //--------------------------
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| 58 | ranlux_state_t local_ranlux_state;
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| 59 |
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| 60 |
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| 61 | // incrementation of the generator state
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| 62 | //---------------------------------------
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| 63 | static inline unsigned long int increment_state(){
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| 64 | unsigned int i = local_ranlux_state.i;
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| 65 | unsigned int j = local_ranlux_state.j;
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| 66 | long int delta = local_ranlux_state.u[j] - local_ranlux_state.u[i]
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| 67 | - local_ranlux_state.carry;
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| 68 |
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| 69 | if (delta & mask_hi){
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| 70 | local_ranlux_state.carry = 1;
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| 71 | delta &= mask_lo;
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| 72 | } else {
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| 73 | local_ranlux_state.carry = 0;
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| 74 | }
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| 75 |
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| 76 | local_ranlux_state.u[i] = delta;
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| 77 |
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| 78 | if (i==0)
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| 79 | i = 23;
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| 80 | else
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| 81 | i--;
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| 82 |
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| 83 | local_ranlux_state.i = i;
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| 84 |
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| 85 | if (j == 0)
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| 86 | j = 23;
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| 87 | else
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| 88 | j--;
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| 89 |
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| 90 | local_ranlux_state.j = j;
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| 91 |
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| 92 | return delta;
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| 93 | }
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| 94 |
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| 95 |
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| 96 | // set generator state
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| 97 | //---------------------
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| 98 | static void ranlux_set(unsigned long int s){
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| 99 | int i;
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| 100 | long int seed;
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| 101 |
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| 102 | if (s==0)
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| 103 | s = 314159265; /* default seed is 314159265 */
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| 104 |
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| 105 | seed = s;
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| 106 |
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| 107 | /* This is the initialization algorithm of F. James, widely in use
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| 108 | for RANLUX. */
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| 109 |
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| 110 | for (i=0;i<24;i++){
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| 111 | unsigned long int k = seed/53668;
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| 112 | seed = 40014*(seed-k*53668)-k*12211;
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| 113 | if (seed<0){
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| 114 | seed += 2147483563;
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| 115 | }
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| 116 | local_ranlux_state.u[i] = seed%two24;
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| 117 | }
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| 118 |
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| 119 | local_ranlux_state.i = 23;
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| 120 | local_ranlux_state.j = 9;
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| 121 | local_ranlux_state.n = 0;
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| 122 | local_ranlux_state.skip = 389-24; // 389 => best decorrelation
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| 123 |
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| 124 | if (local_ranlux_state.u[23]&mask_hi){
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| 125 | local_ranlux_state.carry = 1;
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| 126 | } else {
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| 127 | local_ranlux_state.carry = 0;
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| 128 | }
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| 129 | }
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| 130 |
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| 131 |
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| 132 | // generator initialization
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| 133 | //--------------------------
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| 134 | void ranlux_init(){
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| 135 | // seed the generator
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| 136 | ranlux_set(0);
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| 137 | }
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| 138 |
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| 139 |
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| 140 | // get random number
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| 141 | //-------------------
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| 142 | unsigned long int ranlux_get(){
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| 143 | const unsigned int skip = local_ranlux_state.skip;
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| 144 | unsigned long int r = increment_state();
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| 145 |
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| 146 | local_ranlux_state.n++;
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| 147 |
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| 148 | if (local_ranlux_state.n == 24){
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| 149 | unsigned int i;
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| 150 | local_ranlux_state.n = 0;
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| 151 | for (i = 0; i < skip; i++)
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| 152 | increment_state();
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| 153 | }
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| 154 |
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| 155 | return r;
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| 156 | }
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| 157 |
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| 158 | // print generator state
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| 159 | //-----------------------
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| 160 | void ranlux_print_state(){
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| 161 | size_t i;
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| 162 | unsigned char *p = (unsigned char *) (&local_ranlux_state);
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| 163 | const size_t n = sizeof (ranlux_state_t);
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| 164 |
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| 165 | for (i=0;i<n;i++){
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| 166 | /* FIXME: we're assuming that a char is 8 bits */
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| 167 | printf("%.2x", *(p+i));
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| 168 | }
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| 169 | }
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| 170 |
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| 171 | }
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