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Pre-compute the cosine table to speed up analysis by ±16%

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This commit is contained in:
Alexander Kojevnikov 2010-08-26 20:58:26 +10:00
parent 103d891325
commit ae571fef7a
1 changed files with 7 additions and 2 deletions
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9
src/spek-pipeline.vala
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@ -38,6 +38,7 @@ namespace Spek {
private Fft.Plan fft;
private int nfft; // Size of the FFT transform.
private float[] coss; // Pre-computed cos table.
private const int NFFT = 64; // Number of FFTs to pre-fetch.
private int input_size;
private int input_pos;
@ -88,6 +89,11 @@ namespace Spek {
} else {
this.sample_rate = cx.sample_rate;
this.nfft = 2 * bands - 2;
this.coss = new float[nfft];
float cf = 2f * (float) Math.PI / this.nfft;
for (int i = 0; i < this.nfft; i++) {
this.coss[i] = Math.cosf (cf * i);
}
this.fft = new Fft.Plan (nfft, threshold);
this.input_size = nfft * (NFFT * 2 + 1);
this.input = new float[input_size];
@ -194,7 +200,6 @@ namespace Spek {
int64 frames = 0;
int64 num_fft = 0;
int64 acc_error = 0;
float cf = 2f * (float) Math.PI / nfft;
int head = 0, tail = 0;
int prev_head = 0;
@ -234,7 +239,7 @@ namespace Spek {
for (int i = 0; i < nfft; i++) {
float val = input[(input_size + head - nfft + i) % input_size];
// Hamming window.
val *= 0.53836f - 0.46164f * Math.cosf (cf * i);
val *= 0.53836f - 0.46164f * coss[i];
fft.input[i] = val;
}
fft.execute ();