/*    This program by D E Knuth is in the public domain and freely copyable
 *    AS LONG AS YOU MAKE ABSOLUTELY NO CHANGES!
 *    It is explained in Seminumerical Algorithms, 3rd edition, Section 3.6
 *    (or in the errata to the 2nd edition, see
 *        http://www-cs-faculty.stanford.edu/~knuth/taocp.html
 *    in the changes to pages 171 and following).
 *
 *    If you find any bugs, please report them immediately to
 *                 taocp@cs.stanford.edu
 *    (and you will be rewarded if the bug is genuine). Thanks! */

#define KK 100                     /* the long lag */
#define LL  37                     /* the short lag */
#define MM (1<<30)                 /* the modulus */ 
#define mod_diff(x,y) (((x)-(y))&(MM-1)) /* subtraction mod MM */

long ran_x[KK];                    /* the generator state */

void ran_array(aa,n)    /* put n new random numbers in aa */
  long *aa;   /* destination */
  int n;      /* array length (must be at least KK) */
{
  register int i,j;
  for (j=0;j<KK;j++) aa[j]=ran_x[j];
  for (;j<n;j++) aa[j]=mod_diff(aa[j-KK],aa[j-LL]);
  for (i=0;i<LL;i++,j++) ran_x[i]=mod_diff(aa[j-KK],aa[j-LL]);
  for (;i<KK;i++,j++) ran_x[i]=mod_diff(aa[j-KK],ran_x[i-LL]);
}

#define TT  70   /* guaranteed separation between streams */
#define is_odd(x)  ((x)&1)          /* units bit of x */
#define evenize(x) ((x)&(MM-2))   /* make x even */

void ran_start(seed)    /* do this before using ran_array */
  long seed;            /* selector for different streams */
{
  register int t,j;
  long x[KK+KK-1];              /* the preparation buffer */
  register long ss=evenize(seed+2);
  for (j=0;j<KK;j++) {
    x[j]=ss;                      /* bootstrap the buffer */
    ss<<=1; if (ss>=MM) ss-=MM-2; /* cyclic shift 29 bits */
  }
  for (;j<KK+KK-1;j++) x[j]=0;
  x[1]++;              /* make x[1] (and only x[1]) odd */
  ss=seed;
  t=TT-1; while (t) {
    for (j=KK-1;j>0;j--) x[j+j]=x[j];  /* "square" */
    for (j=KK+KK-2;j>KK-LL;j-=2) x[KK+KK-1-j]=evenize(x[j]);
    for (j=KK+KK-2;j>=KK;j--) if(is_odd(x[j])) {
      x[j-(KK-LL)]=mod_diff(x[j-(KK-LL)],x[j]);
      x[j-KK]=mod_diff(x[j-KK],x[j]);
    }
    if (is_odd(ss)) {              /* "multiply by z" */
      for (j=KK;j>0;j--)  x[j]=x[j-1];
      x[0]=x[KK];            /* shift the buffer cyclically */
      if (is_odd(x[KK])) x[LL]=mod_diff(x[LL],x[KK]);
    }
    if (ss) ss>>=1; else t--;
  }
  for (j=0;j<LL;j++) ran_x[j+KK-LL]=x[j];
  for (;j<KK;j++) ran_x[j-LL]=x[j];
}