Task 12 is done

2025.05.09/dist/Krivoruchenko_SK/solve.c

@@ -315,3 +315,64 @@ double t11_solve (
 }
 
 // -------
+
+int t12_solve (
+		double (*xt) (double), 
+		double (*yt) (double),
+		double a, double b,
+		double eps, double *res
+) {	
+	int it;
+	
+	double xa = xt(a), ya = yt(a);
+	double xb = xt(b), yb = yt(b);
+	double xl = xa, yl = yb;
+
+	int n = 2;
+	double h = (b - a) * 0.5;
+	double x = xb - xl;
+	double y = yb - yl;
+	double len_n = sqrt(x * x + y * y);
+
+	for (it = 1; it <= MAX_ITER; ++it)
+	{
+		double tn = a + h;
+		double len_2n = 0;
+
+		for (int i = 1; i < n; i++)
+		{
+			double xc = xt(tn);
+			double yc = yt(tn);
+
+			x = xc - xl;
+			y = yc - yl;
+			len_2n += sqrt(x * x + y * y);
+			
+			xl = xc;
+			yl = yc;
+			tn += h;
+		}
+
+		x = xb - xl;
+		y = yb - yl;
+		len_2n += sqrt(x * x + y * y);
+
+		h *= 0.5;
+
+		if (fabs(len_2n - len_n) < eps)
+			break;
+		
+		xl = xa;
+		yl = ya;
+
+		len_n = len_2n;
+		n <<= 1;
+	}
+
+	if (it > MAX_ITER) 
+		return -1;
+	
+	*res = len_n;
+
+	return n;
+}