src/audio/fdct.cc


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#include "dct.h"
#include "util/math.h"
#include <math.h>

void fdct_512(const float input[DCT_SIZE], float output[DCT_SIZE]) {
  float scale_k0 = sqrtf(1.0f / DCT_SIZE);
  float scale_kn = sqrtf(2.0f / DCT_SIZE);

  for (int k = 0; k < DCT_SIZE; ++k) {
    float sum = 0.0f;
    for (int n = 0; n < DCT_SIZE; ++n) {
      sum += input[n] * cosf((PI / DCT_SIZE) * (n + 0.5f) * k);
    }
    float scale = (k == 0) ? scale_k0 : scale_kn;
    output[k] = sum * scale;
  }
}