#include <stdio.h>
#include <stddef.h>
#include <string.h>
#include <stdarg.h>
#include <stdlib.h>
#include <math.h>
#include "geostat.h"

/* prebuild_gwn      */
/* Produce a first construction in real space of the Gaussian white noise */
/* grid:  structure defining the grid          */
/*n: vector with the number of cells along the */
/*   X, Y and Z axes for the underlying grid   */
/*   i = [0 1 2]                               */
/*   --> 0 0 0        : n will be computed and */
/*   updated as output                         */
/*   --> nx ny nz: these dimensions are used   */
/*realin: structure defining a realization -   */
/*        must be a Gaussian white noise       */
/*realization: structure defining a realization*/

void prebuild_gwn(struct grid_mod grid,int n[3],struct realization_mod *realin,double *realization,int solver)

  {
    int i,j,k,maille0,maille1;
    int ntot;

    ntot=n[0]*n[1]*n[2];
    realization[0]=0.;
    if (solver==1)
      {
	for (i=0;i<ntot;i++)
	  {
	    realization[i+1]=(*realin).vector[i];
	  }
      }
    else
      {
	for ( k = 1; k <= n[2]; k++) {
	  for (j = 1; j <= n[1]; j++) {
	    for (i = 1; i <= n[0]; i++) {
	      maille1 = i+(j-1+(k-1)*n[1])*n[0];
	      if (i <= grid.NX && j <= grid.NY && k <= grid.NZ) {
		maille0 = i-1+(j-1+(k-1)*grid.NY)*grid.NX;
		realization[maille1] = (*realin).vector[maille0];
	      } else {
		realization[maille1] = 0.;
	      }
	    }
	  }
	}
      }
    return;
  }