--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Meerwald-dir/frid2_common.c	Fri Dec 20 13:08:59 2024 +0100
@@ -0,0 +1,220 @@
+#include "frid2_common.h"
+#include "signature-utils.h"
+#include "wm.h"
+
+extern char *progname;
+
+void embed_low_freq(double **dcts, int cols, int rows, double alpha, int verbose) {
+  int n;
+  int row, col, dir;
+
+  n = 0;
+  row = col = 0;
+  dir = 1;
+  while (n < nbit_signature) {
+    double d, x;
+    int embed;
+    int out;
+
+    col -= dir;
+    row += dir;
+    if (col < 0) { dir = -1; col = 0; }
+    if (col >= cols) { dir = 1; col = cols - 1; row += 2; }
+    if (row < 0) { dir = 1; row = 0; }
+    if (row >= rows) { dir = -1; row = rows - 1; col += 2; }
+
+    d = dcts[row][col];
+    if (fabs(d) <= 1.0) {
+      if (verbose > 3)
+        fprintf(stderr, "%s: bit #%d - skipped (%d/%d)\n", progname, n, col, row);
+      continue;
+    }
+
+    embed = 2 * get_signature_bit(n) - 1;
+
+    x = (d > 0.0) ? 1.0 : -1.0;
+    out = 1;
+    while (fabs(x) < fabs(d)) {
+      x *= FORWARD_STEP(alpha);
+      out =- out;
+    }
+
+    if (out != embed) {
+      if (fabs(d - x) < fabs(d - x * BACKWARD_STEP(alpha)))
+        x *= FORWARD_STEP(alpha);
+      else
+        x *= BACKWARD_STEP(alpha);
+    }
+
+    d =  (x + x * BACKWARD_STEP(alpha)) / 2.0;
+
+    if (verbose > 3)
+      fprintf(stderr, "%s: embedding bit #%d (= %d) at (%d/%d): %f -> %f\n", progname, n, get_signature_bit(n), col, row, dcts[row][col], d);
+
+    dcts[row][col] = d;
+
+    n++;
+  }
+}
+
+void embed_med_freq(double **dcts, int cols, int rows, double gamma, int seed, int verbose) {
+  // select mid-frequency (30%) coefficients
+  int start = (int) (0.35 * rows * cols + 0.5);
+  int end = (int) (0.65 * rows * cols + 0.5);
+
+  double *vector;
+  int x = 0, y = 0, dir = 1;
+  int i, j;
+
+  vector = malloc((end - start) * sizeof(double));
+  for (i = 0; i < (end - start); i++)
+    vector[i] = 0.0;
+
+  // create pseudo-random vector
+  srandom(seed);
+  for (i = 0; i < nbit_signature; i++) {
+    if (get_signature_bit(i))
+      random();
+    for (j = 0; j < (end - start); j++)
+      vector[j] += (double) (random() & RAND_MAX) / (double) RAND_MAX - 0.5;
+    if (!get_signature_bit(i))
+      random();
+  }
+
+  for (i = 0; i < (end - start); i++)
+    vector[i] /= sqrt(nbit_signature);
+
+  for (i = 0; i < end; i++) {
+    // zig-zag scan
+    x -= dir;
+    y += dir;
+    if (x < 0) { dir = -1; x = 0; }
+    if (x >= cols) { dir = 1; x = cols - 1; y += 2; }
+    if (y < 0) { dir = 1; y = 0; }
+    if (y >= rows) { dir = -1; y = rows - 1; x += 2; }
+
+    // embed vector
+    if ((i - start) >= 0) {
+//      fprintf(stderr, "%d/%d: %f -> %f\n", x, y, dcts[y][x], dcts[y][x] + gamma * vector[i - start]);
+      dcts[y][x] += gamma * vector[i - start];
+    }
+  }
+
+  free(vector);
+}
+
+double detect_low_freq(double **dcts, int cols, int rows, double alpha, double beta, int verbose) {
+  int n;
+  int row, col, dir;
+  double sum1, sum2;
+
+  n = 0;
+  row = col = 0;
+  dir = 1;
+  sum1 = sum2 = 0.0;
+  while (n < nbit_signature1) {
+    double d, x;
+    int detect;
+    int out;
+
+    col -= dir;
+    row += dir;
+    if (col < 0) { dir = -1; col = 0; }
+    if (col >= cols) { dir = 1; col = cols - 1; row += 2; }
+    if (row < 0) { dir = 1; row = 0; }
+    if (row >= rows) { dir = -1; row = rows - 1; col += 2; }
+
+    d = dcts[row][col];
+    if (fabs(d) <= 1.0) {
+      if (verbose > 3)
+        fprintf(stderr, "%s: bit #%d - skipped (%d/%d)\n", progname, n, col, row);
+      continue;
+    }
+
+    detect = 2 * get_signature1_bit(n) - 1;
+
+    x = (d > 0.0) ? 1.0 : -1.0;
+    out = 1;
+    while (fabs(x) < fabs(d)) {
+      x *= FORWARD_STEP(alpha);
+      out =- out;
+    }
+
+    if (verbose > 3)
+      fprintf(stderr, "%s: detected bit #%d (= %d) at (%d/%d): %f\n", progname, n, out > 0 ? 1 : 0, col, row, d);
+
+    set_signature2_bit(n, out > 0 ? 1 : 0);
+    sum1 += pow(fabs(d), beta) * out * detect;
+    sum2 += pow(fabs(d), beta);
+
+    n++;
+  }
+
+  return sum1 / sum2;
+}
+
+double detect_med_freq(double **dcts, int cols, int rows, int seed, int verbose) {
+  int i, j, k;
+  int start= (int) (0.35 * rows * cols + 0.5);
+  int end = (int) (.65 * rows * cols + 0.5);
+
+  int sum, sum1, sum2;
+  int x = 0, y = 0, dir = 1;
+  double *vector;
+  int startx, starty, startdir;
+  double corr[2];
+  double correlation;
+
+  // locate start positions
+  for (i = 0; i < start; i++) {
+    x -= dir;
+    y += dir;
+    if (x < 0) { dir = -1; x = 0; }
+    if (x >= cols) { dir = 1; x = cols - 1; y += 2; }
+    if (y < 0) { dir = 1; y = 0; }
+    if (y >= rows) { dir = -1; y = rows - 1; x += 2; }
+  }
+
+  // save start positions
+  startx = x;
+  starty = y;
+  startdir = dir;
+  srandom(seed);
+
+  vector = malloc((end - start) * sizeof(double));
+
+  for (i = 0; i < nbit_signature1; i++) {
+
+    for (j = 0; j <= (end - start); j++)
+      vector[j] = (double) (random() & RAND_MAX) / (double) RAND_MAX - 0.5;
+
+    for (j = 0; j <= 1; j++) {
+      x = startx;
+      y = starty;
+      dir = startdir;
+      corr[j] = 0;
+
+      for (k = 0; start + k < end; k++) {
+        x -= dir;
+        y += dir;
+        if (x < 0) { dir = -1; x = 0; }
+        if (x >= cols) { dir = 1; x = cols - 1; y += 2; }
+        if (y < 0) { dir = 1; y = 0; }
+        if (y >= rows) { dir = -1; y = rows - 1; x += 2; }
+        corr[j] += dcts[y][x] * vector[k + j];
+      }
+    }
+
+    set_signature2_bit(i,  (corr[0] >= corr[1]) ? 0 : 1);
+  }
+
+  sum = 0; sum1 = 0; sum2 = 0;
+  for (i = 0; i < nbit_signature1; i++) {
+    sum += get_signature1_bit(i) * get_signature2_bit(i);
+    sum1 += get_signature1_bit(i) *  get_signature1_bit(i);
+    sum2 += get_signature2_bit(i) * get_signature2_bit(i);
+  }
+  correlation = (double) sum / (sqrt(sum1) * sqrt(sum2));
+
+  return correlation;
+}