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1 #include "frid2_common.h"
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2 #include "signature.h"
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3 #include "wm.h"
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4
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5 extern char *progname;
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6
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7 void embed_low_freq(double **dcts, int cols, int rows, double alpha, int verbose) {
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8 int n;
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9 int row, col, dir;
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10
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11 n = 0;
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12 row = col = 0;
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13 dir = 1;
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14 while (n < nbit_signature) {
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15 double d, x;
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16 int embed;
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17 int out;
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18
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19 col -= dir;
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20 row += dir;
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21 if (col < 0) { dir = -1; col = 0; }
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22 if (col >= cols) { dir = 1; col = cols - 1; row += 2; }
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23 if (row < 0) { dir = 1; row = 0; }
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24 if (row >= rows) { dir = -1; row = rows - 1; col += 2; }
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25
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26 d = dcts[row][col];
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27 if (fabs(d) <= 1.0) {
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28 if (verbose > 3)
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29 fprintf(stderr, "%s: bit #%d - skipped (%d/%d)\n", progname, n, col, row);
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30 continue;
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31 }
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32
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33 embed = 2 * get_signature_bit(n) - 1;
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34
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35 x = (d > 0.0) ? 1.0 : -1.0;
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36 out = 1;
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37 while (fabs(x) < fabs(d)) {
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38 x *= FORWARD_STEP(alpha);
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39 out =- out;
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40 }
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41
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42 if (out != embed) {
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43 if (fabs(d - x) < fabs(d - x * BACKWARD_STEP(alpha)))
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44 x *= FORWARD_STEP(alpha);
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45 else
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46 x *= BACKWARD_STEP(alpha);
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47 }
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48
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49 d = (x + x * BACKWARD_STEP(alpha)) / 2.0;
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50
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51 if (verbose > 3)
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52 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);
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53
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54 dcts[row][col] = d;
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55
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56 n++;
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57 }
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58 }
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59
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60 void embed_med_freq(double **dcts, int cols, int rows, double gamma, int seed, int verbose) {
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61 // select mid-frequency (30%) coefficients
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62 int start = (int) (0.35 * rows * cols + 0.5);
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63 int end = (int) (0.65 * rows * cols + 0.5);
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64
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65 double *vector;
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66 int x = 0, y = 0, dir = 1;
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67 int i, j;
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68
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69 vector = malloc((end - start) * sizeof(double));
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70 for (i = 0; i < (end - start); i++)
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71 vector[i] = 0.0;
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72
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73 // create pseudo-random vector
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74 srandom(seed);
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75 for (i = 0; i < nbit_signature; i++) {
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76 if (get_signature_bit(i))
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77 random();
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78 for (j = 0; j < (end - start); j++)
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79 vector[j] += (double) (random() & RAND_MAX) / (double) RAND_MAX - 0.5;
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80 if (!get_signature_bit(i))
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81 random();
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82 }
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83
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84 for (i = 0; i < (end - start); i++)
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85 vector[i] /= sqrt(nbit_signature);
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86
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87 for (i = 0; i < end; i++) {
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88 // zig-zag scan
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89 x -= dir;
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90 y += dir;
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91 if (x < 0) { dir = -1; x = 0; }
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92 if (x >= cols) { dir = 1; x = cols - 1; y += 2; }
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93 if (y < 0) { dir = 1; y = 0; }
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94 if (y >= rows) { dir = -1; y = rows - 1; x += 2; }
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95
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96 // embed vector
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97 if ((i - start) >= 0) {
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98 // fprintf(stderr, "%d/%d: %f -> %f\n", x, y, dcts[y][x], dcts[y][x] + gamma * vector[i - start]);
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99 dcts[y][x] += gamma * vector[i - start];
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100 }
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101 }
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102
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103 free(vector);
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104 }
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105
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106 double detect_low_freq(double **dcts, int cols, int rows, double alpha, double beta, int verbose) {
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107 int n;
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108 int row, col, dir;
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109 double sum1, sum2;
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110
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111 n = 0;
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112 row = col = 0;
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113 dir = 1;
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114 sum1 = sum2 = 0.0;
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115 while (n < nbit_signature1) {
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116 double d, x;
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117 int detect;
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118 int out;
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119
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120 col -= dir;
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121 row += dir;
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122 if (col < 0) { dir = -1; col = 0; }
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123 if (col >= cols) { dir = 1; col = cols - 1; row += 2; }
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124 if (row < 0) { dir = 1; row = 0; }
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125 if (row >= rows) { dir = -1; row = rows - 1; col += 2; }
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126
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127 d = dcts[row][col];
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128 if (fabs(d) <= 1.0) {
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129 if (verbose > 3)
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130 fprintf(stderr, "%s: bit #%d - skipped (%d/%d)\n", progname, n, col, row);
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131 continue;
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132 }
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133
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134 detect = 2 * get_signature1_bit(n) - 1;
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135
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136 x = (d > 0.0) ? 1.0 : -1.0;
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137 out = 1;
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138 while (fabs(x) < fabs(d)) {
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139 x *= FORWARD_STEP(alpha);
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140 out =- out;
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141 }
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142
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143 if (verbose > 3)
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144 fprintf(stderr, "%s: detected bit #%d (= %d) at (%d/%d): %f\n", progname, n, out > 0 ? 1 : 0, col, row, d);
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145
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146 set_signature2_bit(n, out > 0 ? 1 : 0);
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147 sum1 += pow(fabs(d), beta) * out * detect;
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148 sum2 += pow(fabs(d), beta);
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149
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150 n++;
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151 }
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152
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153 return sum1 / sum2;
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154 }
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155
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156 double detect_med_freq(double **dcts, int cols, int rows, int seed, int verbose) {
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157 int i, j, k;
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158 int start= (int) (0.35 * rows * cols + 0.5);
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159 int end = (int) (.65 * rows * cols + 0.5);
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160
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161 int sum, sum1, sum2;
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162 int x = 0, y = 0, dir = 1;
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163 double *vector;
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164 int startx, starty, startdir;
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165 double corr[2];
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166 double correlation;
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167
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168 // locate start positions
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169 for (i = 0; i < start; i++) {
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170 x -= dir;
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171 y += dir;
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172 if (x < 0) { dir = -1; x = 0; }
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173 if (x >= cols) { dir = 1; x = cols - 1; y += 2; }
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174 if (y < 0) { dir = 1; y = 0; }
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175 if (y >= rows) { dir = -1; y = rows - 1; x += 2; }
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176 }
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177
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178 // save start positions
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179 startx = x;
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180 starty = y;
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181 startdir = dir;
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182 srandom(seed);
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183
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184 vector = malloc((end - start) * sizeof(double));
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185
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186 for (i = 0; i < nbit_signature1; i++) {
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187
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188 for (j = 0; j <= (end - start); j++)
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189 vector[j] = (double) (random() & RAND_MAX) / (double) RAND_MAX - 0.5;
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190
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191 for (j = 0; j <= 1; j++) {
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192 x = startx;
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193 y = starty;
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194 dir = startdir;
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195 corr[j] = 0;
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196
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197 for (k = 0; start + k < end; k++) {
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198 x -= dir;
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199 y += dir;
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200 if (x < 0) { dir = -1; x = 0; }
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201 if (x >= cols) { dir = 1; x = cols - 1; y += 2; }
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202 if (y < 0) { dir = 1; y = 0; }
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203 if (y >= rows) { dir = -1; y = rows - 1; x += 2; }
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204 corr[j] += dcts[y][x] * vector[k + j];
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205 }
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206 }
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207
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208 set_signature2_bit(i, (corr[0] >= corr[1]) ? 0 : 1);
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209 }
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210
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211 sum = 0; sum1 = 0; sum2 = 0;
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212 for (i = 0; i < nbit_signature1; i++) {
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213 sum += get_signature1_bit(i) * get_signature2_bit(i);
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214 sum1 += get_signature1_bit(i) * get_signature1_bit(i);
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215 sum2 += get_signature2_bit(i) * get_signature2_bit(i);
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216 }
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217 correlation = (double) sum / (sqrt(sum1) * sqrt(sum2));
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218
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219 return correlation;
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220 }
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