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 *    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

 *        https://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];

}