extract newton's method

firmware/config/boards/hellen/hellen_board_id.cpp

@@ -87,26 +87,14 @@ float HellenBoardIdSolver::solve(float Tc1, float Tc2, float x0, float y, float
 	k3 = iC * (Tc1 - Tc2);
 
 	// the same method works for R (if C is known) or C (if R is known)
-	float Xcur, Xnext;
-	Xnext = x0;
+	auto result = NewtonsMethodSolver::solve(x0, deltaX, 20);
 
-	// since we had https://github.com/rusefi/rusefi/issues/4084 let's add paranoia check
-	// All real cases seem to converge in <= 5 iterations, so we don't need to try more than 20.
-	int safetyLimit = 20;
-	do {
-		if (safetyLimit-- < 0) {
-			firmwareError(OBD_PCM_Processor_Fault, "hellen boardID is broken");
-			break;
-		}
-		Xcur = Xnext;
-		Xnext = Xcur - fx(Xcur) / dfx(Xcur);
+	if (!result) {
+		firmwareError(OBD_PCM_Processor_Fault, "hellen boardID is broken");
+		return 0;
+	}
 
-#ifdef HELLEN_BOARD_ID_DEBUG
-		efiPrintf ("* %f", Xnext);
-#endif /* HELLEN_BOARD_ID_DEBUG */
-	} while (absF(Xnext - Xcur) > deltaX);
-
-	return Xnext;
+	return result.Value;
 }
 
 float HellenBoardIdFinderBase::findClosestResistor(float R, bool testOnlyMajorSeries, int *rIdx) {

firmware/config/boards/hellen/hellen_board_id.h

@@ -27,15 +27,15 @@ public:
 // We need to solve the following equation for R or C:
 //   X^Td - X^(Tc1+Td) + X^(Tc2-Tc1) - 1 = 0
 // where: X = exp(-1/(RC))
-class HellenBoardIdSolver
+class HellenBoardIdSolver : public NewtonsMethodSolver
 {
 public:
-	float fx(float x) {
+	float fx(float x) override {
 		return exp(k1 / x) - exp(k2 / x) + exp(k3 / x) - 1.0;
 	}
 
 	// first-order derivative
-	float dfx(float x) {
+	float dfx(float x) override {
 		return (-1.0f / (x * x)) * (k1 * exp(k1 / x) - k2 * exp(k2 / x) + k3 * exp(k3 / x));
 	}
 

firmware/libfirmware

@@ -1 +1 @@
-Subproject commit 8e65946de929c7fafa00ca23f57c86b4e9c4177f
+Subproject commit 163cee4279c83f46efccd279ce22006d039fb2bb