sysy-data/hidden_functional/sy/37_dct.sy

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// reference:
// https://stackoverflow.com/questions/8310749/discrete-cosine-transform-dct-implementation-c
const int MAX_DIM_X = 8, MAX_DIM_Y = 8;
float test_block[MAX_DIM_X][MAX_DIM_Y];
float test_dct[MAX_DIM_X][MAX_DIM_Y];
float test_idct[MAX_DIM_X][MAX_DIM_Y];
const float PI = 3.14159265359, TWO_PI = 6.28318530718, EPSILON = 1e-6;
float my_fabs(float x) {
if (x > 0) return x;
return -x;
}
float p(float x) { return 3 * x - 4 * x * x * x; }
float my_sin_impl(float x) {
if (my_fabs(x) <= EPSILON) return x;
return p(my_sin_impl(x / 3.0));
}
float my_sin(float x) {
if (x > TWO_PI || x < -TWO_PI) {
int xx = x / TWO_PI;
x = x - xx * TWO_PI;
}
if (x > PI) x = x - TWO_PI;
if (x < -PI) x = x + TWO_PI;
return my_sin_impl(x);
}
float my_cos(float x) { return my_sin(x + PI / 2); }
void write_mat(float mat[][MAX_DIM_Y], int n, int m) {
int i = 0;
while (i < n) {
putfloat(mat[i][0]);
int j = 1;
while (j < m) {
putch(32);
putfloat(mat[i][j]);
j = j + 1;
}
putch(10);
i = i + 1;
}
putch(10);
}
void dct(float dct_mat[][MAX_DIM_Y], float mat[][MAX_DIM_Y], int n, int m) {
int u = 0;
while (u < n) {
int v = 0;
while (v < m) {
dct_mat[u][v] = 0;
int i = 0;
while (i < n) {
int j = 0;
while (j < m) {
dct_mat[u][v] =
dct_mat[u][v] + mat[i][j] * my_cos(PI / n * (i + 1. / 2.) * u) *
my_cos(PI / m * (j + 1. / 2.) * v);
j = j + 1;
}
i = i + 1;
}
v = v + 1;
}
u = u + 1;
}
}
void idct(float mat[][MAX_DIM_Y], float dct_mat[][MAX_DIM_Y], int n, int m) {
int u = 0;
while (u < n) {
int v = 0;
while (v < m) {
mat[u][v] = 1 / 4. * dct_mat[0][0];
int i, j;
i = 1;
while (i < n) {
mat[u][v] = mat[u][v] + 1 / 2. * dct_mat[i][0];
i = i + 1;
}
j = 1;
while (j < m) {
mat[u][v] = mat[u][v] + 1 / 2. * dct_mat[0][j];
j = j + 1;
}
i = 1;
while (i < n) {
j = 1;
while (j < m) {
mat[u][v] = mat[u][v] + dct_mat[i][j] *
my_cos(PI / n * (u + 1. / 2.) * i) *
my_cos(PI / m * (v + 1. / 2.) * j);
j = j + 1;
}
i = i + 1;
}
mat[u][v] = mat[u][v] * 2. / n * 2. / m;
v = v + 1;
}
u = u + 1;
}
}
int main() {
int dim_x = getint(), dim_y = getint();
int i = 0;
while (i < dim_x) {
int j = 0;
while (j < dim_y) {
test_block[i][j] = getfloat();
j = j + 1;
}
i = i + 1;
}
dct(test_dct, test_block, dim_x, dim_y);
write_mat(test_dct, dim_x, dim_y);
idct(test_idct, test_dct, dim_x, dim_y);
write_mat(test_idct, dim_x, dim_y);
return 0;
}