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filterKernel.c
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filterKernel.c
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// emcc -O3 -s WASM=1 filterKernel.c -o filterKernel.wasm --no-entry
#include <emscripten.h>
float _PI = 3.14159265359;
float _SAMPLERATE = 44100;
float inputBuffer[128];
float outputBuffer[128];
double p0, p1, p2, p3;
double p32, p33, p34;
float resonance;
EMSCRIPTEN_KEEPALIVE
void setResonance(float r) {
resonance = r;
}
float cutoff;
EMSCRIPTEN_KEEPALIVE
void setCutoff(float c){
cutoff = c * 2 * _PI / _SAMPLERATE;
cutoff = (cutoff > 1) ? 1 : cutoff;
}
inline double fast_tanh(double x) {
double x2 = x * x;
return x * (27.0 + x2) / (27.0 + 9.0 * x2);
}
EMSCRIPTEN_KEEPALIVE
void init() {
p0 = p1 = p2 = p3 = p32 = p33 = p34 = 0.0f;
setCutoff(1000.0f);
setResonance(0.70f);
}
EMSCRIPTEN_KEEPALIVE
float* inputBufferPtr() {
return inputBuffer;
}
EMSCRIPTEN_KEEPALIVE
float* outputBufferPtr() {
return outputBuffer;
}
EMSCRIPTEN_KEEPALIVE
void filter() {
for (int i=0 ; i<128 ; i++) {
double k = resonance * 4;
double out = p3 * 0.360891 + p32 * 0.417290 + p33 * 0.177896 + p34 * 0.0439725;
p34 = p33; p33 = p32; p32 = p3;
p0 += (fast_tanh(inputBuffer[i] - k * out) - fast_tanh(p0)) * cutoff;
p1 += (fast_tanh(p0) - fast_tanh(p1)) * cutoff;
p2 += (fast_tanh(p1) - fast_tanh(p2)) * cutoff;
p3 += (fast_tanh(p2) - fast_tanh(p3)) * cutoff;
outputBuffer[i] = out;
}
}