/* 54-BIT (double) IMPLEMENTATION IN C OF THE "MRG32K3A" GENERATOR
   ===============================================================
 
   Sebastian.Egner@philips.com, Mar-2002, in ANSI-C and Scheme 48 0.57

   This code is a C-implementation of Pierre L'Ecuyer's MRG32k3a generator.
   The code uses (double)-arithmetics, assuming that it covers the range
   {-2^53..2^53-1} exactly (!). The code of the generator is based on the 
   L'Ecuyer's own implementation of the generator. Please refer to the
   file 'mrg32k3a.scm' for more information about the method.

   The method provides the following functions via the C/Scheme
   interface of Scheme 48 0.57 to 'mrg32k3a-b.scm':

      s48_value mrg32k3a_pack_state1(s48_value state);
      s48_value mrg32k3a_unpack_state1(s48_value state);
      s48_value mrg32k3a_random_range();
      s48_value mrg32k3a_random_integer(s48_value state, s48_value range);
      s48_value mrg32k3a_random_real(s48_value state);

   As Scheme48 FIXNUMs cannot cover the range {0..m1-1}, we break up
   all values x in the state into x0+x1*w, where w = 2^16 = 65536.
   The procedures in Scheme correct for that.

   compile this file with:
     gcc -c -I $SCHEME48 mrg32k3a-b.c

   history of this file: 
     SE, 18-Mar-2002: initial version
     SE, 22-Mar-2002: interface changed
     SE, 25-Mar-2002: tested with Scheme 48 0.57 in c/srfi-27
     SE, 27-Mar-2002: cleaned
     SE, 13-May-2002: bug found by Shiro Kawai removed
*/

#include "scheme48.h" /* $SCHEME48/c/scheme48.h */
#include <sys/time.h>

#ifndef NULL
  #define NULL 0
#endif
/* maximum value for random_integer: min(S48_MAX_FIXNUM_VALUE, m1) */
#define m_max (((long)1 << 29) - 1)

/* The Generator
   =============
*/

/* moduli of the components */
#define m1 4294967087.0
#define m2 4294944443.0

/* representation of the state in C */
typedef struct {
  double 
    x10, x11, x12,
    x20, x21, x22; 
} state_t;

/* recursion coefficients of the components */
#define a12  1403580.0
#define a13n  810728.0
#define a21   527612.0
#define a23n 1370589.0

/* normalization factor 1/(m1 + 1) */
#define norm 2.328306549295728e-10


/* the actual generator */

static double mrg32k3a(state_t *s) { /* (double), in {0..m1-1} */
  double x10, x20, y;
  long   k10, k20;

/* #define debug 1 */

#if defined(debug)
  printf(
    "state = {%g %g %g %g %g %g};\n",
    s->x10, s->x11, s->x12, 
    s->x20, s->x21, s->x22
  );
#endif

  /* component 1 */
  x10  = a12*(s->x11) - a13n*(s->x12);
  k10  = x10 / m1;
  x10 -= k10 * m1;
  if (x10 < 0.0)
    x10 += m1;
  s->x12 = s->x11;
  s->x11 = s->x10;
  s->x10 = x10;

  /* component 2 */
  x20  = a21*(s->x20) - a23n*(s->x22);
  k20  = x20 / m2;
  x20 -= k20 * m2;
  if (x20 < 0.0)
    x20 += m2;
  s->x22 = s->x21;
  s->x21 = s->x20;
  s->x20 = x20;

  /* combination of component */
  y = x10 - x20;
  if (y < 0.0)
    y += m1;
  return y;
}

/* Exported Interface
   ==================
*/

s48_value mrg32k3a_pack_state1(s48_value state) {
  s48_value result;
  state_t   s;

#define REF(i) (double)s48_extract_integer(S48_VECTOR_REF(state, (long)(i)))

  /* copy the numbers from state into s */
  s.x10 = REF( 0) + 65536.0 * REF( 1);
  s.x11 = REF( 2) + 65536.0 * REF( 3);
  s.x12 = REF( 4) + 65536.0 * REF( 5);
  s.x20 = REF( 6) + 65536.0 * REF( 7);
  s.x21 = REF( 8) + 65536.0 * REF( 9);
  s.x22 = REF(10) + 65536.0 * REF(11);

#undef REF

  /* box s into a Scheme object */
  result = S48_MAKE_VALUE(state_t);
  S48_SET_VALUE(result, state_t, s);
  return result;
}

s48_value mrg32k3a_unpack_state1(s48_value state) {
  s48_value result;
  state_t   s;

  /* unbox s from the Scheme object */
  s = S48_EXTRACT_VALUE(state, state_t);

  /* make and fill a Scheme vector with the numbers */
  result = s48_make_vector((long)12, S48_FALSE);

#define SET(i, x) { \
  long x1 = (long)((x) / 65536.0); \
  long x0 = (long)((x) - 65536.0 * (double)x1); \
  S48_VECTOR_SET(result, (long)(i+0), s48_enter_integer(x0)); \
  S48_VECTOR_SET(result, (long)(i+1), s48_enter_integer(x1)); }

  SET( 0, s.x10);
  SET( 2, s.x11);
  SET( 4, s.x12);
  SET( 6, s.x20);
  SET( 8, s.x21);
  SET(10, s.x22);

#undef SET

  return result;
}

s48_value mrg32k3a_random_range(void) {
  return s48_enter_fixnum(m_max);  
}

s48_value mrg32k3a_random_integer(s48_value state, s48_value range) {
  long    result;
  state_t s;
  long    n;
  double  x, q, qn, xq;

  s = S48_EXTRACT_VALUE(state, state_t);
  n = s48_extract_integer(range);
  if (!( ((long)1 <= n) && (n <= m_max) ))
    s48_raise_range_error(n, (long)1, m_max);

  /* generate result in {0..n-1} using the rejection method */
  q  = (double)( (unsigned long)(m1 / (double)n) );
  qn = q * n;
  do {
    x = mrg32k3a(&s);
  } while (x >= qn);
  xq = x / q;

  /* check the range */
  if (!( (0.0 <= xq) && (xq < (double)m_max) ))
    s48_raise_range_error((long)xq, (long)0, m_max);

  /* return result */
  result = (long)xq;
  S48_SET_VALUE(state, state_t, s);
  return s48_enter_fixnum(result);
}

s48_value mrg32k3a_random_real(s48_value state) {
  state_t s;
  double  x;

  s = S48_EXTRACT_VALUE(state, state_t);
  x = (mrg32k3a(&s) + 1.0) * norm;
  S48_SET_VALUE(state, state_t, s);
  return s48_enter_double(x);
}

/* Kludge for scsh */
static s48_value current_time(void){
  struct timeval tv;
  gettimeofday(&tv, NULL);
  return s48_enter_integer(tv.tv_sec);
}


/* Exporting the C values to Scheme
   ================================
*/

void s48_init_srfi_27(void) {
  S48_EXPORT_FUNCTION(mrg32k3a_pack_state1);
  S48_EXPORT_FUNCTION(mrg32k3a_unpack_state1);
  S48_EXPORT_FUNCTION(mrg32k3a_random_range);
  S48_EXPORT_FUNCTION(mrg32k3a_random_integer);
  S48_EXPORT_FUNCTION(mrg32k3a_random_real);
  S48_EXPORT_FUNCTION(current_time);
}