Add Kochubei's solve

2025.05.02/05Ex/solve.c

@@ -0,0 +1,70 @@
+#include "solve.h"
+
+#include <math.h>
+#include <float.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <string.h>
+
+int t1_solve (
+		double (*f) (double), 
+		double a, double b, 
+		double eps, int m, double *x
+) {
+	int it = 0;
+	uint64_t bits;
+	double c = DBL_MAX, y, y_a = f(a), y_b = f(b);
+	bool sgn_a, sgn_b, sgn_c;
+
+	memcpy(&bits, &y_a, sizeof(bits));
+	sgn_a = (bits >> 63) & 1;
+	memcpy(&bits, &y_b, sizeof(bits));
+	sgn_b = (bits >> 63) & 1;
+
+	if (fabs(y_a) - eps < DBL_EPSILON)
+	{
+		*x = a;
+		return 1;
+	} if (fabs(y_b) - eps < DBL_EPSILON)
+	{
+		*x = b;
+		return 1;
+	}
+
+	if (sgn_a == sgn_b)
+	{
+		*x = DBL_MAX;
+		return -1;
+	}
+	
+	for (it = 1; it <= m; ++it)
+	{
+		c = (a + b) * 0.5;
+		y = f(c);
+		
+		memcpy(&bits, &y, sizeof(bits));
+		sgn_c = (bits >> 63) & 1;
+		
+		if (fabs(y) - eps < DBL_EPSILON)
+			break;
+		else if ((fabs(c - a) < DBL_EPSILON) || (fabs(c - b) < DBL_EPSILON))
+			it = m+1;
+		else if (sgn_c == sgn_a)
+		{
+			a = c;
+			y_a = y;
+		} else if (sgn_c == sgn_b)
+		{
+			b = c;
+			y_b = y;
+		}
+	}
+	
+	if (it > m)
+		it = -1;
+	
+	*x = c;
+
+	return it;
+}
+