/* ---------------------------------------------------------------------- */
 /* gem.c - original version of {gem_residues_enum} */ 

void gem_residues_enum(gem_ref_t root, int d, int rcol[], int r, int scol[], int s, int na, gem_ref_t nodes[], int *nnP)
  { demand((d >= 0) && (d <= gem_MAX_DIM), "invalid dimension");
    int i;
    for(i = 0; i < r; i++) { demand((rcol[i] >= 0) && (rcol[i] <= d), "invalid R-color"); }
    for(i = 0; i < s; i++) { demand((scol[i] >= 0) && (scol[i] <= d), "invalid S-color"); }
    
    int nn = 0;  /* Number of nodes seen so far. */
    
    /* List of marked nodes: */
    gem_ref_t *mark = notnull(malloc(na*sizeof(gem_ref_t)), "no mem");
    int nnMark = 0;
    
    auto void mark_node(gem_ref_t p);
    auto int is_marked(gem_ref_t p);
    
    void mark_node(gem_ref_t p)
      { if ((p->label < 0) || (p->label >= (nnMark))||(mark[p->label]!=p))
          { mark[nnMark] = p;
            mark[nnMark]->label = nnMark;
            (nnMark)++;
          }
      }

    int is_marked(gem_ref_t p)
      { return ((p->label >= 0) && (p->label < nnMark) && (mark[p->label] == p));
      }

    /* The {r}-stack: */
    gem_ref_t *rstack = notnull(malloc(na*sizeof(gem_ref_t)), "no mem");
    int nnr = 0;
    /* The {s}-stack: */
    gem_ref_t *sstack = notnull(malloc(na*sizeof(gem_ref_t)), "no mem");
    sstack[0] = root;
    int nns = 1;
    while((nnr>0) || (nns>0))
      { gem_ref_t p;
        if (nnr == 0) 
          { p = sstack[--nns];
            if (! is_marked(p)) 
              { demand(nn < na, "too many nodes");
                nodes[nn++] = p;
              }
          }
        else
          { p = rstack[--nnr]; }
        if (!is_marked(p))
          { mark_node(p);
            for(i = 0; i < r; i++) { demand(nnr < na, "too many nodes"); rstack[nnr++] = p->adj[rcol[i]]; }
            for(i = 0; i < s; i++) { demand(nns < na, "too many nodes"); sstack[nns++] = p->adj[scol[i]]; }
          }
      }
    for(i = 0; i < nn;  i++) { nodes[i]->label = i; }
    free(mark);
    free(rstack);
    free(sstack);
    (*nnP) = nn;
  }

/* ---------------------------------------------------------------------- */
    
 // used to collect data on a traversal
typedef struct {
  gem_ref_t head;
  gem_ref_t tail;
  int color;
} Edge;



                         // a GEM node will have gem_MAX_DIM pointers
//#define gem_MAX_NODES  10000000  // size of the stack used for traversing a gem.
#define MAX_GEM_EDGES ((gem_MAX_NODES*gem_MAX_DIM+1)/2)
// used to collect data on a traversal
typedef struct {
  gem_ref_thead;
  gem_ref_ttail;
  int color;
} Edge;