/* rng/ranlxs.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 M. Luescher's second generation

   version of the RANLUX generator.

   Thanks to Martin Luescher for providing information on this

   generator.

 */

static unsigned long int ranlxs_get (void *vstate);

static inline double ranlxs_get_double (void *vstate);

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

static void ranlxs0_set (void *state, unsigned long int s);

static void ranlxs1_set (void *state, unsigned long int s);

static void ranlxs2_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 int snext[24] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13,

                              14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 0};

static const double sbase = 16777216.0;         /* 2^24 */

static const double sone_bit = 1.0 / 16777216.0;        /* 1/2^24 */

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

static const double shift = 268435456.0;        /* 2^28 */

#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], ydbl[12];  /* doubles first so they are 8-byte aligned */

    double carry;

    float xflt[24];

    unsigned int ir;

    unsigned int jr;

    unsigned int is;

    unsigned int is_old;

    unsigned int pr;

  }

ranlxs_state_t;

static void increment_state (ranlxs_state_t * state);

static void

increment_state (ranlxs_state_t * state)

{

  int k, kmax, m;

  double x, y1, y2, y3;

  float *xflt = state->xflt;

  double *xdbl = state->xdbl;

  double *ydbl = state->ydbl;

  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;

      ydbl[ir] = y2 + shift;

      ir = next[ir];

      jr = next[jr];

    }

  ydbl[ir] = xdbl[ir] + shift;

  for (k = next[ir]; k > 0;)

    {

      ydbl[k] = xdbl[k] + shift;

      k = next[k];

    }

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

    {

      x = xdbl[k];

      y2 = ydbl[k] - shift;

      if (y2 > x)

        y2 -= sone_bit;

      y1 = (x - y2) * sbase;

      xflt[m++] = (float) y1;

      xflt[m++] = (float) y2;

    }

  state->ir = ir;

  state->is = 2 * ir;

  state->is_old = 2 * ir;

  state->jr = jr;

  state->carry = carry;

}

static inline double

ranlxs_get_double (void *vstate)

{

  ranlxs_state_t *state = (ranlxs_state_t *) vstate;

  const unsigned int is = snext[state->is];

  state->is = is;

  if (is == state->is_old)

    increment_state (state);

  return state->xflt[state->is];

}

static unsigned long int

ranlxs_get (void *vstate)

{

  return ranlxs_get_double (vstate) * 16777216.0;       /* 2^24 */

}

static void

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

{

  ranlxs_state_t *state = (ranlxs_state_t *) vstate;

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

  double x, y;

  long int seed;

  if (s == 0)

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

  seed = s;

  i = seed & 0x7FFFFFFFUL;  /* Allowed seeds for ranlxs are 0 .. 2^31-1 */

  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 (m = 1; m <= 48; ++m)

        {

          y = (double) xbit[ibit];

          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 = 0;

  state->jr = 7;

  state->is = 23;

  state->is_old = 0;

  state->pr = luxury;

}

static void

ranlxs0_set (void *vstate, unsigned long int s)

{

  ranlxs_set_lux (vstate, s, 109);

}

void

ranlxs1_set (void *vstate, unsigned long int s)

{

  ranlxs_set_lux (vstate, s, 202);

}

static void

ranlxs2_set (void *vstate, unsigned long int s)

{

  ranlxs_set_lux (vstate, s, 397);

}

static const gsl_rng_type ranlxs0_type =

{"ranlxs0",                     /* name */

 0x00ffffffUL,                  /* RAND_MAX */

 0,                             /* RAND_MIN */

 sizeof (ranlxs_state_t),

 &ranlxs0_set,

 &ranlxs_get,

 &ranlxs_get_double};

static const gsl_rng_type ranlxs1_type =

{"ranlxs1",                     /* name */

 0x00ffffffUL,                  /* RAND_MAX */

 0,                             /* RAND_MIN */

 sizeof (ranlxs_state_t),

 &ranlxs1_set,

 &ranlxs_get,

 &ranlxs_get_double};

static const gsl_rng_type ranlxs2_type =

{"ranlxs2",                     /* name */

 0x00ffffffUL,                  /* RAND_MAX */

 0,                             /* RAND_MIN */

 sizeof (ranlxs_state_t),

 &ranlxs2_set,

 &ranlxs_get,

 &ranlxs_get_double};

const gsl_rng_type *gsl_rng_ranlxs0 = &ranlxs0_type;

const gsl_rng_type *gsl_rng_ranlxs1 = &ranlxs1_type;

const gsl_rng_type *gsl_rng_ranlxs2 = &ranlxs2_type;