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gck.c
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gck.c
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// Josh Allmann, 11 April 2013.
// Based on "The Gray Code Filter Kernels" by G. Ben-Artzi, et al.
// http://cs.haifa.ac.il/~hagit/papers/PAMI07-GrayCodeKernels.pdf
// to compile: gcc -o gck2d gck2d.c -lm
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <math.h>
#include <string.h>
typedef struct GCKPoint {
int x, y;
} GCKPoint;
static void gck_path(GCKPoint *p, int kern_size, int bases)
{
// Calculate the route for traversal between NxN kernels.
// Roughly follows a diagonal pattern starting from the top-left.
GCKPoint *r = p, *w = r + 1;
// initialize first element
r->x = 0; r->y = 0;
bases -= 1;
kern_size -= 1; // check from 0...(N - 1), not 1...N
while (bases) {
if (r->x == 0 && r->y < kern_size) {
w->x = 0;
w->y = r->y + 1;
w++;
bases--;
if (!bases) break;
}
if (r->x >= kern_size){
r++;
continue;
}
w->y = r->y;
w->x = r->x + 1;
w++;
r++;
bases--;
}
}
static int gck_gc(int a)
{
// return the gray code representation of a
return (a >> 1) ^ a;
}
static int gck_prefix(int a, int b, int bits)
{
// find the common bitwise prefix between a and b.
int c = 0, n = 1 << bits;
while (n && (a & n) == (b & n)) {
c += 1;
n >>= 1;
}
return c;
}
static void gck_2d_dc_in(uint8_t *data, int *dc, int data_len, int kern_size)
{
int i, out_w = data_len + kern_size - 1;
dc[0] = data[0];
for (i = 1; i < kern_size; i++) {
dc[i] = data[i] + dc[i-1];
}
for (; i < data_len; i++) {
dc[i] = data[i] + dc[i-1] - data[i - kern_size];
}
for (; i < out_w; i++) {
dc[i] = dc[i - 1] - data[i - kern_size];
}
}
static void gck_2d_dc(uint8_t *udata, int *dc, int data_w, int data_h, int kern_size)
{
int i, j, out_w = kern_size + data_w - 1, size;
int *pr = NULL; // previous row
int *ppr = NULL;
int *t, *u, *data, *odc = dc; // preserve original
if (data_w < kern_size || data_h < kern_size) {
fprintf(stderr, "Kernel larger than data. Exiting\n");
exit(1);
}
size = (data_w + kern_size - 1) * (data_h + kern_size - 1);
t = u = calloc(size, sizeof(int));
ppr = t;
data = t + out_w;
pr = odc;
dc = odc + out_w;
// horizontal
for (i = 0; i < data_h; i++) {
gck_2d_dc_in(udata, u, data_w, kern_size);
udata += data_w;
u += out_w;
}
// vertical
memcpy(odc, t, size*sizeof(int));
for (i = 1; i < kern_size; i++) {
for (j = 0; j < out_w; j++) dc[j] = data[j] + pr[j];
dc += out_w;
pr += out_w;
data += out_w;
}
for (; i < data_h; i++) {
for (j = 0; j < out_w; j++) dc[j] = data[j] + pr[j] - ppr[j];
dc += out_w;
pr += out_w;
ppr += out_w;
data += out_w;
}
for (; i < data_h + kern_size - 1; i++) {
for (j = 0; j < out_w; j++) dc[j] = pr[j] - ppr[j];
dc += out_w;
pr += out_w;
ppr += out_w;
}
free(t);
}
static void gck_2d_horiz(int *cur, int a, int *prev, int b,
int w, int h, int klen)
{
int i, j, len = w + klen - 1, hlen = h + klen - 1;
int bits = log2(klen) - 1; // kernel length, in bits
int c = gck_gc(a), d = gck_gc(b);
int prefix = gck_prefix(d, c, bits);
int delta = 1 << prefix;
int sign = (c >> (bits - prefix)) & 1;
for (j = 0; j < hlen; j++) {
for (i = 0; i < delta; i++) cur[i] = -prev[i];
for (; i < len; i++) {
if (sign) cur[i] = prev[i - delta] - cur[i - delta] - prev[i];
else cur[i] = cur[i - delta] - prev[i - delta] - prev[i];
}
cur += len;
prev += len;
}
}
static void gck_2d_vert(int *cur, int a, int *prev, int b,
int w, int h, int klen)
{
int i, j, hlen = h + klen - 1, wlen = w + klen - 1;
int bits = log2(klen) - 1; // kernel length, in bits
int c = gck_gc(a), d = gck_gc(b);
int prefix = gck_prefix(c, d, bits);
int delta = 1 << prefix;
int sign = (c >> (bits - prefix)) & 1;
int *curd = cur, *prevd = prev;
for (i = 0; i < delta; i++) {
for (j = 0; j < wlen; j++) cur[j] = -prev[j];
cur += wlen;
prev += wlen;
}
for (; i < hlen; i++) {
for (j = 0; j < wlen; j++) {
if (sign) cur[j] = prevd[j] - curd[j] - prev[j];
else cur[j] = curd[j] - prevd[j] - prev[j];
}
cur += wlen;
curd += wlen;
prev += wlen;
prevd += wlen;
}
}
static void gck_get_adj(GCKPoint *p1, GCKPoint *p2)
{
// get adjacent points by undoing the diagonal construction
if (!p1->x) {
if (!p1->y) {
p2->x = p2->y = 0;
return;
}
p2->y = p1->y - 1;
p2->x = 0;
return;
}
p2->x = p1->x - 1;
p2->y = p1->y;
}
static int gck_adj_idx(GCKPoint *path, GCKPoint *p, int idx)
{
// linear search for index of adjacency. Given a point, the
// adjacency will always be before it, so search backwards.
while (idx >= 0) {
if (path->x == p->x && path->y == p->y) return idx;
path--;
idx--;
}
fprintf(stderr, "Point does not exist in path\n");
return -1;
}
static void print_path(GCKPoint *path, int nb)
{
int i, j;
char *m = malloc(nb*nb);
memset(m, ' ', nb*nb);
printf("Traversal Path for Kernels\n");
for (i = 0; i < nb; i++) {
GCKPoint p;
gck_get_adj(&path[i], &p);
j = gck_adj_idx(&path[i], &p, i);
printf("%2d : (%d %d) adjacency %d - (%d %d)\n", i, path[i].x, path[i].y, j, p.x, p.y);
m[path[i].y * nb + path[i].x] += '+';
}
free(m);
}
static int gck_direction(GCKPoint *p1, GCKPoint *p2)
{
// return 0 for vertical shifts, 1 for horizontal
if (p1->x == p2->x) return 0;
return 1;
}
int* gck_calc_2d(uint8_t *data, int w, int h, int kern_size, int bases)
{
int i, wh = (w+kern_size - 1) * (h + kern_size - 1);
int size = wh * bases;
int *res = calloc(size, sizeof(int)); // TODO cacheline padding?
GCKPoint adj, *path = malloc(bases * sizeof(GCKPoint));
gck_path(path, kern_size, bases);
//print_path(path, bases);
gck_2d_dc(data, res, w, h, kern_size);
for (i = 1; i < bases; i++) {
gck_get_adj(&path[i], &adj);
int j = gck_adj_idx(&path[i], &adj, i);
if (-1 == j) return NULL;
int horiz = gck_direction(&path[i], &adj);
int *prev = res + j * wh;
int *cur = res + i * wh;
if (horiz) gck_2d_horiz(cur, path[i].x, prev, adj.x, w, h, kern_size);
else gck_2d_vert(cur, path[i].y, prev, adj.y, w, h, kern_size);
}
free(path);
return res;
}
int* gck_alloc_buffer(int w, int h, int kern_size, int bases)
{
int kw = w - kern_size + 1, kh = h - kern_size + 1;
int* res = malloc(kw*kh*bases*sizeof(int));
if (!res) {
fprintf(stderr, "Unable to allocate GCK buffer\n");
}
return res;
}
#if 0
static void prep_data(uint8_t *data, int w, int h)
{
int i, j;
printf("Original Data:\n");
for (i = 0; i < w; i++) {
for (j = 0; j < h; j++) {
int k = (i & 1) ? 8 - j : j + 1;
data[j + i * w] = k;
printf("%4d", k);
}
printf("\n");
}
}
static void print_data(int *data, int w, int h)
{
int i, j;
for (i = 0; i < h; i++) {
for (j = 0; j < w; j++) {
printf("%3d ", data[j + i * w]);
}
printf("\n");
}
}
static void print_bases(int *data, int w, int h,
int kern_size, int bases)
{
int i, kw = w+kern_size-1, kh = h+kern_size-1;
printf("Filtered Results, Per Base:\n");
for (i = 0; i < bases; i++) {
printf("%4d:\n", i);
print_data(data, kw, kh);
printf("\n");
data += kw*kh;
}
}
static void weirdcase()
{
uint8_t q[] = {163, 163, 165, 165, 167, 167, 165, 165, 163, 163, 165, 166, 163, 162, 163, 165, 164, 164, 164, 167, 164, 164, 163, 160, 164, 164, 165, 166, 167, 163, 159, 157, 165, 165, 165, 163, 165, 162, 166, 164, 165, 165, 165, 165, 168, 164, 165, 164, 166, 166, 167, 163, 164, 166, 166, 164, 166, 166, 167, 165, 163, 165, 165, 163};
int bases = 25;
int *valid_res, *res, *interleaved;
valid_res = gck_alloc_buffer(1, 1, 1, bases);
interleaved = gck_alloc_buffer(1, 1, 1, bases);
res = gck_calc_2d(q, 8, 8, 8, bases);
gck_truncate_data(res, 8, 8, 8, bases, valid_res);
gck_interleave_data(valid_res, 1, 1, bases, interleaved, bases);
print_bases(res, 8, 8, 8, bases);
print_bases(interleaved, bases, 1, 1, 1);
free(res);
free(valid_res);
free(interleaved);
}
#define W 8
#define H 8
#define KERN_LEN 4
#define BASES 16
#define VW (W - KERN_LEN + 1)
#define VH (H - KERN_LEN + 1)
int main()
{
int *res, *valid_res, *interleaved;
uint8_t data[W*H];
valid_res = gck_alloc_buffer(VW, VH, 1, BASES);
interleaved = gck_alloc_buffer(VW, VH, 1, BASES);
prep_data(data, W, H);
res = gck_calc_2d(data, W, H, KERN_LEN, BASES);
gck_truncate_data(res, W, H, KERN_LEN, BASES, valid_res);
gck_interleave_data(valid_res, VW, VH, BASES, interleaved, BASES);
print_bases(res, W, H, KERN_LEN, BASES);
print_bases(valid_res, VW, VH, 1, BASES);
print_bases(interleaved, KERN_LEN, KERN_LEN, 1, BASES);
free(res);
free(valid_res);
free(interleaved);
//weirdcase();
return 0;
}
#endif
#undef W
#undef H
#undef KERN_LEN
#undef BASES
#undef VW
#undef VH