Imported healpix tree

external/healpix/cxxsupport/planck_rng.h

@@ -0,0 +1,154 @@
+/*
+ *  This file is part of libcxxsupport.
+ *
+ *  libcxxsupport is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  libcxxsupport is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with libcxxsupport; if not, write to the Free Software
+ *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+
+/*
+ *  libcxxsupport is being developed at the Max-Planck-Institut fuer Astrophysik
+ *  and financially supported by the Deutsches Zentrum fuer Luft- und Raumfahrt
+ *  (DLR).
+ */
+
+/*! \file planck_rng.h
+ *  This file contains the random number generator
+ *  used by the Planck LevelS package.
+ *  The generator is a C++ port of the xorshift generator xor128() described
+ *  in Marsaglia, Journal of Statistical Software 2003, vol 8.
+ *  It has a period of 2^128 - 1.
+ *
+ *  Copyright (C) 2003, 2004, 2005 Max-Planck-Society
+ *  \author Martin Reinecke
+ */
+
+#ifndef PLANCK_RNG_H
+#define PLANCK_RNG_H
+
+#include <cmath>
+#include "error_handling.h"
+
+/*! C++ port of the xorshift generator xor128() described in Marsaglia,
+    Journal of Statistical Software 2003, vol 8.
+    It has a period of 2^128 - 1. */
+class planck_rng
+  {
+  private:
+    unsigned int x,y,z,w;
+    double small, gset;
+    bool empty;
+
+    void twiddle (unsigned int &v)
+      {
+      for (int i=0; i<9; ++i)
+        {
+        v ^= v<<13;
+        v ^= v>>17;
+        v ^= v<<5;
+        }
+      }
+
+    void init_rng ()
+      {
+      // avoid zero seeds
+      if (x==0) x = 123456789;
+      if (y==0) y = 362436069;
+      if (z==0) z = 521288629;
+      if (w==0) w = 88675123;
+
+      // shuffle the bits of the seeds
+      twiddle(x); twiddle(y); twiddle(z); twiddle(w);
+
+      // burn in the RNG
+      for (int i=0; i<16; ++i)
+        int_rand_uni();
+      }
+
+  public:
+    /*! Initializes the generator with 0 to 4 seed values. */
+    planck_rng (unsigned int x1=123456789, unsigned int y1=362436069,
+                unsigned int z1=521288629, unsigned int w1=88675123)
+      : x(x1), y(y1), z(z1), w(w1),
+        small(1./(1.+double(0xFFFFFFFF))), gset(0.), empty(true)
+      {
+      planck_assert (sizeof(unsigned int)==4, "wrong integer size for RNG");
+      init_rng();
+      }
+
+    /*! Re-initializes the generator with 0 to 4 seed values. */
+    void seed (unsigned int x1=123456789, unsigned int y1=362436069,
+      unsigned int z1=521288629, unsigned int w1=88675123)
+      {
+      x = x1; y = y1; z = z1; w = w1;
+      empty = true;
+      init_rng();
+      }
+
+    /*! Returns uniformly distributed random integer numbers from the
+        interval [0;0xFFFFFFFF]. */
+    unsigned int int_rand_uni()
+      {
+      unsigned int t = x^(x<<11);
+      x = y;
+      y = z;
+      z = w;
+
+      return w=(w^(w>>19))^(t^(t>>8));
+      }
+
+    //! Returns uniformly distributed random numbers from the interval [0;1[.
+    double rand_uni()
+      {
+      return small*int_rand_uni();
+      }
+
+    //! Returns random numbers with Gaussian distribution (mean=0, sigma=1).
+    /*! Uses rand_uni() internally. */
+    double rand_gauss()
+      {
+      using namespace std;
+      if (empty)
+        {
+        double v1,v2,rsq;
+        do
+          {
+          v1=2*rand_uni()-1.;
+          v2=2*rand_uni()-1.;
+          rsq=v1*v1+v2*v2;
+          }
+        while ((rsq>=1) || (rsq==0));
+        double fac=sqrt(-2*log(rsq)/rsq);
+        gset=v1*fac;
+        empty=false;
+        return v2*fac;
+        }
+      else
+        {
+        empty=true;
+        return gset;
+        }
+      }
+
+    //! Returns exponentially distributed random numbers (mean=1, nonnegative)
+    /*! Uses rand_uni() internally. */
+    double rand_exp()
+      {
+      using namespace std;
+      double val=rand_uni();
+      if (val==0.) val=1.;
+      return -log(val);
+      }
+  };
+
+#endif