/* rng/ranlxd.c

 * 

 * Copyright (C) 1996, 1997, 1998, 1999, 2000, 2007 James Theiler, Brian Gough

 * 

 * This program 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 3 of the License, or (at

 * your option) any later version.

 * 

 * This program 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 this program; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.

 */

#include <config.h>

#include <stdlib.h>

#include <gsl/gsl_rng.h>

/* This is an implementation of Martin Luescher's second generation

   double-precision (48-bit) version of the RANLUX generator. 

   Thanks to Martin Luescher for providing information on this

   generator.

*/

static inline unsigned long int ranlxd_get (void *vstate);

static double ranlxd_get_double (void *vstate);

static void ranlxd_set_lux (void *state, unsigned long int s, unsigned int luxury);

static void ranlxd1_set (void *state, unsigned long int s);

static void ranlxd2_set (void *state, unsigned long int s);

static const int next[12] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 0};

static const double one_bit = 1.0 / 281474976710656.0;  /* 1/2^48 */

#define RANLUX_STEP(x1,x2,i1,i2,i3)      \

          x1=xdbl[i1] - xdbl[i2];        \

          if (x2 < 0)                    \

          {                              \

            x1-=one_bit;                 \

            x2+=1;                       \

          }                              \

         xdbl[i3]=x2

typedef struct

  {

    double xdbl[12]; 

    double carry;

    unsigned int ir;

    unsigned int jr;

    unsigned int ir_old;

    unsigned int pr;

  }

ranlxd_state_t;

static inline void increment_state (ranlxd_state_t * state);

static inline void

increment_state (ranlxd_state_t * state)

{

  int k, kmax;

  double y1, y2, y3;

  double *xdbl = state->xdbl;

  double carry = state->carry;

  unsigned int ir = state->ir;

  unsigned int jr = state->jr;

  for (k = 0; ir > 0; ++k)

    {

      y1 = xdbl[jr] - xdbl[ir];

      y2 = y1 - carry;

      if (y2 < 0)

        {

          carry = one_bit;

          y2 += 1;

        }

      else

        {

          carry = 0;

        }

      xdbl[ir] = y2;

      ir = next[ir];

      jr = next[jr];

    }

  kmax = state->pr - 12;

  for (; k <= kmax; k += 12)

    {

      y1 = xdbl[7] - xdbl[0];

      y1 -= carry;

      RANLUX_STEP (y2, y1, 8, 1, 0);

      RANLUX_STEP (y3, y2, 9, 2, 1);

      RANLUX_STEP (y1, y3, 10, 3, 2);

      RANLUX_STEP (y2, y1, 11, 4, 3);

      RANLUX_STEP (y3, y2, 0, 5, 4);

      RANLUX_STEP (y1, y3, 1, 6, 5);

      RANLUX_STEP (y2, y1, 2, 7, 6);

      RANLUX_STEP (y3, y2, 3, 8, 7);

      RANLUX_STEP (y1, y3, 4, 9, 8);

      RANLUX_STEP (y2, y1, 5, 10, 9);

      RANLUX_STEP (y3, y2, 6, 11, 10);

      if (y3 < 0)

        {

          carry = one_bit;

          y3 += 1;

        }

      else

        {

          carry = 0;

        }

      xdbl[11] = y3;

    }

  kmax = state->pr;

  for (; k < kmax; ++k)

    {

      y1 = xdbl[jr] - xdbl[ir];

      y2 = y1 - carry;

      if (y2 < 0)

        {

          carry = one_bit;

          y2 += 1;

        }

      else

        {

          carry = 0;

        }

      xdbl[ir] = y2;

      ir = next[ir];

      jr = next[jr];

    }

  state->ir = ir;

  state->ir_old = ir;

  state->jr = jr;

  state->carry = carry;

}

static inline unsigned long int

ranlxd_get (void *vstate)

{

  return ranlxd_get_double (vstate) * 4294967296.0;     /* 2^32 */

}

static double

ranlxd_get_double (void *vstate)

{

  ranlxd_state_t *state = (ranlxd_state_t *) vstate;

  int ir = state->ir;

  state->ir = next[ir];

  if (state->ir == state->ir_old)

    increment_state (state);

  return state->xdbl[state->ir];

}

static void

ranlxd_set_lux (void *vstate, unsigned long int s, unsigned int luxury)

{

  ranlxd_state_t *state = (ranlxd_state_t *) vstate;

  int ibit, jbit, i, k, l, xbit[31];

  double x, y;

  long int seed;

  if (s == 0)

    s = 1;                      /* default seed is 1 */

  seed = s;

  i = seed & 0xFFFFFFFFUL;

  for (k = 0; k < 31; ++k)

    {

      xbit[k] = i % 2;

      i /= 2;

    }

  ibit = 0;

  jbit = 18;

  for (k = 0; k < 12; ++k)

    {

      x = 0;

      for (l = 1; l <= 48; ++l)

        {

          y = (double) ((xbit[ibit] + 1) % 2);

          x += x + y;

          xbit[ibit] = (xbit[ibit] + xbit[jbit]) % 2;

          ibit = (ibit + 1) % 31;

          jbit = (jbit + 1) % 31;

        }

      state->xdbl[k] = one_bit * x;

    }

  state->carry = 0;

  state->ir = 11;

  state->jr = 7;

  state->ir_old = 0;

  state->pr = luxury;

}

static void

ranlxd1_set (void *vstate, unsigned long int s)

{

  ranlxd_set_lux (vstate, s, 202);

}

static void

ranlxd2_set (void *vstate, unsigned long int s)

{

  ranlxd_set_lux (vstate, s, 397);

}

static const gsl_rng_type ranlxd1_type =

{"ranlxd1",                     /* name */

 0xffffffffUL,                  /* RAND_MAX */

 0,                             /* RAND_MIN */

 sizeof (ranlxd_state_t),

 &ranlxd1_set,

 &ranlxd_get,

 &ranlxd_get_double};

static const gsl_rng_type ranlxd2_type =

{"ranlxd2",                     /* name */

 0xffffffffUL,                  /* RAND_MAX */

 0,                             /* RAND_MIN */

 sizeof (ranlxd_state_t),

 &ranlxd2_set,

 &ranlxd_get,

 &ranlxd_get_double};

const gsl_rng_type *gsl_rng_ranlxd1 = &ranlxd1_type;

const gsl_rng_type *gsl_rng_ranlxd2 = &ranlxd2_type;