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| /* Linear quadtree implementation based on
*
* K. Aizawa, K. Motomura, S. Kimura, R. Kadowaki and J. Fan
* "Constant time neighbor finding in quadtrees"
* ISCCSP 2008, Malta, 12-14 March 2008.
* http://www.lcad.icmc.usp.br/~jbatista/procimg/quadtree_neighbours.pdf
*
* This uses a Z-grid ordering
*/
#define GRIDNAME "Linear quadtree"
#include <stdio.h>
#include <assert.h>
#define _I (quad_x(point.i))
#define _J (quad_y(point.i))
typedef struct {
Data * d;
int i, level, depth;
} Point;
#define data(k,l) point.d[quad_neighbor(point.i, k, l)]
/* the maximum level */
static int quad_r;
static int size (int l)
{
return ((1 << (2*(l + 1))) - 1)/3;
}
int level (int p)
{
p = 3*p + 1;
int l = 0;
while (p > 0) { p /= 4; l++; }
return l - 1;
}
int code (int p, int l)
{
return (p - size (l - 1)) << 2*(quad_r - l);
}
int index (int code, int l)
{
return size(l - 1) + (code >> 2*(quad_r - l));
}
int quad_x (int p)
{
int n = code (p, level(p)), a = 0, m = 1, b = 1;
for (int i = 0; i < 2*quad_r - 1; i += 2, m *= 4, b *= 2)
a += ((m & n) != 0)*b;
return a;
}
int quad_y (int p)
{
int n = code (p, level(p)), a = 0, m = 2, b = 1;
for (int i = 1; i < 2*quad_r; i += 2, m *= 4, b *= 2)
a += ((m & n) != 0)*b;
return a;
}
int repeat (int a)
{
int s = 0;
for (int i = 0; i < quad_r; i++, a *= 4)
s += a;
return s;
}
static int quad_left, quad_right = 1, quad_top = 2, quad_bottom;
#define quad(n, d) ((((n|quad_bottom)+(d&quad_left))&quad_left)|(((n|quad_left)+(d&quad_bottom))&quad_bottom))
static int quad_id[3][3];
int quad_neighbor (int p, int i, int j)
{
int d = quad_id[i+1][j+1];
if (d == 0) return p;
int l = level (p);
int n = code (p, l);
d <<= (2*(quad_r - l));
return index (quad(n, d), l);
}
int quad_neighbor_finest (int p, int i, int j)
{
int d = quad_id[i+1][j+1];
if (d == 0) return p;
int s = size (quad_r - 1);
int n = p - s;
return s + quad(n,d);
}
void * quadtree (int r, size_t s)
{
quad_r = r;
void * q = malloc (s*size (r));
quad_left = repeat (1);
quad_bottom = repeat (2);
quad_id[0][2] = quad_top|quad_left;
quad_id[1][2] = quad_top;
quad_id[2][2] = quad_top|quad_right;
quad_id[0][1] = quad_left; quad_id[1][1] = 0; quad_id[2][1] = quad_right;
quad_id[0][0] = quad_bottom|quad_left; quad_id[1][0] = quad_bottom;
quad_id[2][0] = quad_bottom|quad_right;
return q;
}
void * init_grid (int n)
{
int depth = 0;
while (n > 1) {
if (n % 2) {
fprintf (stderr, "quadtree: N must be a power-of-two\n");
exit (1);
}
n /= 2;
depth++;
}
void * q = quadtree (depth, sizeof (Data));
return q;
}
void free_grid (void * m)
{
free (m);
}
#define STACKSIZE 20
#define _push(c,d) \
{ _s++; stack[_s].i = c; stack[_s].stage = d; }
#define _pop(c,d) \
{ c = stack[_s].i; d = stack[_s].stage; _s--; }
#define foreach(grid) \
{ \
struct { int i, stage; } stack[STACKSIZE]; int _s = -1; /* the stack */ \
Point point; \
point.d = grid; \
point.depth = quad_r; \
_push (0, 0); /* the root cell */ \
while (_s >= 0) { \
int stage; \
_pop (point.i, stage); \
if (!stage) { \
point.level = level (point.i); \
if (point.level < point.depth) { \
_push (point.i, 1); \
_push (4*point.i + 1, 0); \
} \
else { \
VARIABLES; \
/* do something */
#define end_foreach() \
} \
} \
else { \
if (stage < 3) \
_push (point.i, stage + 1); \
_push (4*point.i + stage + 1, 0); \
} \
} \
}
#if 0
int main (int argc, char * argv[])
{
void * grid = init_grid (atoi (argv[1]));
foreach (grid) {
printf ("%d %d %d\n", I, J, point.level);
} end_foreach();
free_grid (grid);
}
#endif
#if 0
int main (int argc, char * argv[])
{
int r = atoi(argv[1]);
void * q = quadtree (r, sizeof (double));
for (int p = size (r - 1); p < size (r); p++) {
int q = neighbor (p, quad_bottom | quad_left, r);
printf ("%d %d %d ( %d , %d ) | ( %d , %d ) ",
p, index (code (p, r), level (p), r), level (p),
x(p, r), y(p, r),
x(q, r), y(q, r));
printf ("\n");
}
return 0;
}
#endif
|
