feat: iterate on SsfStepDetector

* use SSF signal instead of accelerometer signal
* use higher BEAT_CORR_THR_{12} for SSF signal
* add absolute SSF_THRESHOLD to ignore small accelero bumps
* compute ssf_threshold according to detected SSF peaks, not the mean (more robust vs. noise)

pasada-lib/iir_filter.cpp

@@ -13,13 +13,13 @@
 #define DEBUG_PRINT(expr) while(0) { expr; }
 #endif
 
-Buf::Buf(size_t N): size(N), n(0) {
+Buf::Buf(size_t N): N(N), n(0) {
     data.resize(N);
     data.assign(N, 0.0);
 }
 void Buf::push(double val) {
     data[n] = val;
-    n = (n+1) % size;
+    n = (n+1) % N;
 }
 
 Filt::Filt(size_t N, size_t shift, size_t offset, std::vector<double> taps): Buf(N), shift(shift), offset(offset), taps(taps) {
@@ -31,9 +31,9 @@ double Filt::filter(double val) {
 }
 double Filt::peek() {
     double sum = 0;
-    for (size_t i = offset; i < this->size; i++) {
+    for (size_t i = offset; i < this->N; i++) {
         //size_t n = (this->n - i + shift - 1) % this->size; // unsigned % size ... bad if u is negative
-        size_t n = (this->size + this->n - i + shift - 1) % this->size;
+        size_t n = (this->N + this->n - i + shift - 1) % this->N;
         DEBUG_PRINT(std::cout << " t[" << i << "] * v[" << n << "]" << std::endl);
         sum += this->data[n] * this->taps[i];
     }
@@ -42,6 +42,12 @@ double Filt::peek() {
 void Filt::push(double val) {
     Buf::push(val);
 }
+void Filt::prime(double val) {
+    data.assign(this->N, val);
+}
+size_t Filt::size() {
+    return this->N;
+}
 
 IirFilter::IirFilter(std::vector<double> b, std::vector<double> a) : x(b.size(), 0, 0, b), y(a.size(), 1, 1, a) {
     if (b.size() != a.size()) throw std::invalid_argument("b.size() != a.size()");