--- /dev/null
+/* sre_random.c
+ *
+ * Portable random number generator, and sampling routines.
+ *
+ * SRE, Tue Oct 1 15:24:11 2002 [St. Louis]
+ * CVS $Id: sre_random.c,v 1.1 2002/10/09 14:26:09 eddy Exp)
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <math.h>
+#include "sre_random.h"
+
+static int sre_randseed = 42; /* default seed for sre_random() */
+
+/* Function: sre_random()
+ *
+ * Purpose: Return a uniform deviate x, 0.0 <= x < 1.0.
+ *
+ * sre_randseed is a static variable, set
+ * by sre_srandom(). When it is non-zero,
+ * we re-seed.
+ *
+ * Implements L'Ecuyer's algorithm for combining output
+ * of two linear congruential generators, plus a Bays-Durham
+ * shuffle. This is essentially ran2() from Numerical Recipes,
+ * sans their nonhelpful Rand/McNally-esque code obfuscation.
+ *
+ * Overflow errors are avoided by Schrage's algorithm:
+ * az % m = a(z%q) - r(z/q) (+m if <0)
+ * where q=m/a, r=m%a
+ *
+ * Requires that long int's have at least 32 bits.
+ * This function uses statics and is NOT THREADSAFE.
+ *
+ * Reference: Press et al. Numerical Recipes in C, 1992.
+ *
+ * Reliable and portable, but slow. Benchmarks on wrasse,
+ * using Linux gcc and Linux glibc rand() (see randspeed, in Testsuite):
+ * sre_random(): 0.5 usec/call
+ * rand(): 0.2 usec/call
+ */
+double
+sre_random(void)
+{
+ static long rnd1; /* random number from LCG1 */
+ static long rnd2; /* random number from LCG2 */
+ static long rnd; /* random number we return */
+ static long tbl[64]; /* table for Bays/Durham shuffle */
+ long x,y;
+ int i;
+
+ /* Magic numbers a1,m1, a2,m2 from L'Ecuyer, for 2 LCGs.
+ * q,r derive from them (q=m/a, r=m%a) and are needed for Schrage's algorithm.
+ */
+ long a1 = 40014;
+ long m1 = 2147483563;
+ long q1 = 53668;
+ long r1 = 12211;
+
+ long a2 = 40692;
+ long m2 = 2147483399;
+ long q2 = 52774;
+ long r2 = 3791;
+
+ if (sre_randseed > 0)
+ {
+ rnd1 = sre_randseed;
+ rnd2 = sre_randseed;
+ /* Fill the table for Bays/Durham */
+ for (i = 0; i < 64; i++) {
+ x = a1*(rnd1%q1); /* LCG1 in action... */
+ y = r1*(rnd1/q1);
+ rnd1 = x-y;
+ if (rnd1 < 0) rnd1 += m1;
+
+ x = a2*(rnd2%q2); /* LCG2 in action... */
+ y = r2*(rnd2/q2);
+ rnd2 = x-y;
+ if (rnd2 < 0) rnd2 += m2;
+
+ tbl[i] = rnd1-rnd2;
+ if (tbl[i] < 0) tbl[i] += m1;
+ }
+ sre_randseed = 0; /* drop the flag. */
+ }/* end of initialization*/
+
+
+ x = a1*(rnd1%q1); /* LCG1 in action... */
+ y = r1*(rnd1/q1);
+ rnd1 = x-y;
+ if (rnd1 < 0) rnd1 += m1;
+
+ x = a2*(rnd2%q2); /* LCG2 in action... */
+ y = r2*(rnd2/q2);
+ rnd2 = x-y;
+ if (rnd2 < 0) rnd2 += m2;
+
+ /* Choose our random number from the table... */
+ i = (int) (((double) rnd / (double) m1) * 64.);
+ rnd = tbl[i];
+ /* and replace with a new number by L'Ecuyer. */
+ tbl[i] = rnd1-rnd2;
+ if (tbl[i] < 0) tbl[i] += m1;
+
+ return ((double) rnd / (double) m1);
+}
+
+/* Function: sre_srandom()
+ *
+ * Purpose: Initialize with a random seed. Seed must be
+ * >= 0 to work; we silently enforce this.
+ */
+void
+sre_srandom(int seed)
+{
+ if (seed < 0) seed = -1 * seed;
+ if (seed == 0) seed = 42;
+ sre_randseed = seed;
+}
+
+/* Function: sre_random_positive()
+ * Date: SRE, Wed Apr 17 13:34:32 2002 [St. Louis]
+ *
+ * Purpose: Assure 0 < x < 1 (positive uniform deviate)
+ */
+double
+sre_random_positive(void)
+{
+ double x;
+ do { x = sre_random(); } while (x == 0.0);
+ return x;
+}
+
+/* Function: ExponentialRandom()
+ * Date: SRE, Mon Sep 6 21:24:29 1999 [St. Louis]
+ *
+ * Purpose: Pick an exponentially distributed random variable
+ * 0 > x >= infinity
+ *
+ * Args: (void)
+ *
+ * Returns: x
+ */
+double
+ExponentialRandom(void)
+{
+ double x;
+
+ do x = sre_random(); while (x == 0.0);
+ return -log(x);
+}
+
+/* Function: Gaussrandom()
+ *
+ * Pick a Gaussian-distributed random variable
+ * with some mean and standard deviation, and
+ * return it.
+ *
+ * Based on RANLIB.c public domain implementation.
+ * Thanks to the authors, Barry W. Brown and James Lovato,
+ * University of Texas, M.D. Anderson Cancer Center, Houston TX.
+ * Their implementation is from Ahrens and Dieter, "Extensions
+ * of Forsythe's method for random sampling from the normal
+ * distribution", Math. Comput. 27:927-937 (1973).
+ *
+ * Impenetrability of the code is to be blamed on its FORTRAN/f2c lineage.
+ *
+ */
+double
+Gaussrandom(double mean, double stddev)
+{
+ static double a[32] = {
+ 0.0,3.917609E-2,7.841241E-2,0.11777,0.1573107,0.1970991,0.2372021,0.2776904, 0.3186394,0.36013,0.4022501,0.4450965,0.4887764,0.5334097,0.5791322,
+ 0.626099,0.6744898,0.7245144,0.7764218,0.8305109,0.8871466,0.9467818,
+ 1.00999,1.077516,1.150349,1.229859,1.318011,1.417797,1.534121,1.67594,
+ 1.862732,2.153875
+ };
+ static double d[31] = {
+ 0.0,0.0,0.0,0.0,0.0,0.2636843,0.2425085,0.2255674,0.2116342,0.1999243,
+ 0.1899108,0.1812252,0.1736014,0.1668419,0.1607967,0.1553497,0.1504094,
+ 0.1459026,0.14177,0.1379632,0.1344418,0.1311722,0.128126,0.1252791,
+ 0.1226109,0.1201036,0.1177417,0.1155119,0.1134023,0.1114027,0.1095039
+ };
+ static double t[31] = {
+ 7.673828E-4,2.30687E-3,3.860618E-3,5.438454E-3,7.0507E-3,8.708396E-3,
+ 1.042357E-2,1.220953E-2,1.408125E-2,1.605579E-2,1.81529E-2,2.039573E-2,
+ 2.281177E-2,2.543407E-2,2.830296E-2,3.146822E-2,3.499233E-2,3.895483E-2,
+ 4.345878E-2,4.864035E-2,5.468334E-2,6.184222E-2,7.047983E-2,8.113195E-2,
+ 9.462444E-2,0.1123001,0.136498,0.1716886,0.2276241,0.330498,0.5847031
+ };
+ static double h[31] = {
+ 3.920617E-2,3.932705E-2,3.951E-2,3.975703E-2,4.007093E-2,4.045533E-2,
+ 4.091481E-2,4.145507E-2,4.208311E-2,4.280748E-2,4.363863E-2,4.458932E-2,
+ 4.567523E-2,4.691571E-2,4.833487E-2,4.996298E-2,5.183859E-2,5.401138E-2,
+ 5.654656E-2,5.95313E-2,6.308489E-2,6.737503E-2,7.264544E-2,7.926471E-2,
+ 8.781922E-2,9.930398E-2,0.11556,0.1404344,0.1836142,0.2790016,0.7010474
+ };
+ static long i;
+ static double snorm,u,s,ustar,aa,w,y,tt;
+
+ u = sre_random();
+ s = 0.0;
+ if(u > 0.5) s = 1.0;
+ u += (u-s);
+ u = 32.0*u;
+ i = (long) (u);
+ if(i == 32) i = 31;
+ if(i == 0) goto S100;
+ /*
+ * START CENTER
+ */
+ ustar = u-(double)i;
+ aa = *(a+i-1);
+S40:
+ if(ustar <= *(t+i-1)) goto S60;
+ w = (ustar-*(t+i-1))**(h+i-1);
+S50:
+ /*
+ * EXIT (BOTH CASES)
+ */
+ y = aa+w;
+ snorm = y;
+ if(s == 1.0) snorm = -y;
+ return (stddev*snorm + mean);
+S60:
+ /*
+ * CENTER CONTINUED
+ */
+ u = sre_random();
+ w = u*(*(a+i)-aa);
+ tt = (0.5*w+aa)*w;
+ goto S80;
+S70:
+ tt = u;
+ ustar = sre_random();
+S80:
+ if(ustar > tt) goto S50;
+ u = sre_random();
+ if(ustar >= u) goto S70;
+ ustar = sre_random();
+ goto S40;
+S100:
+ /*
+ * START TAIL
+ */
+ i = 6;
+ aa = *(a+31);
+ goto S120;
+S110:
+ aa += *(d+i-1);
+ i += 1;
+S120:
+ u += u;
+ if(u < 1.0) goto S110;
+ u -= 1.0;
+S140:
+ w = u**(d+i-1);
+ tt = (0.5*w+aa)*w;
+ goto S160;
+S150:
+ tt = u;
+S160:
+ ustar = sre_random();
+ if(ustar > tt) goto S50;
+ u = sre_random();
+ if(ustar >= u) goto S150;
+ u = sre_random();
+ goto S140;
+}
+
+
+/* Functions: DChoose(), FChoose()
+ *
+ * Purpose: Make a random choice from a normalized distribution.
+ * DChoose() is for double-precision vectors;
+ * FChoose() is for single-precision float vectors.
+ * Returns the number of the choice.
+ */
+int
+DChoose(double *p, int N)
+{
+ double roll; /* random fraction */
+ double sum; /* integrated prob */
+ int i; /* counter over the probs */
+
+ roll = sre_random();
+ sum = 0.0;
+ for (i = 0; i < N; i++)
+ {
+ sum += p[i];
+ if (roll < sum) return i;
+ }
+ return (int) (sre_random() * N); /* bulletproof */
+}
+int
+FChoose(float *p, int N)
+{
+ float roll; /* random fraction */
+ float sum; /* integrated prob */
+ int i; /* counter over the probs */
+
+ roll = sre_random();
+ sum = 0.0;
+ for (i = 0; i < N; i++)
+ {
+ sum += p[i];
+ if (roll < sum) return i;
+ }
+ return (int) (sre_random() * N); /* bulletproof */
+}
+
+
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