add more math function

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@1420 bbd45198-f89e-11dd-88c7-29a3b14d5316

components/libc/newlib/math.c

@@ -166,3 +166,95 @@ double cos(double x)
     return result;
 }
 
+static const int N = 100;
+
+double coef(int n)
+{
+ 	double t;
+
+	if (n == 0) 
+	{
+		return 0;
+	}
+
+ 	t = 1.0/n;
+
+ 	if (n%2 == 0) 
+	{
+		t = -t;
+	}
+
+ 	return t;
+}
+
+double horner(double x)
+{
+	double u = coef(N);
+ 	int i;
+
+ 	for(i=N-1; i>=0; i--)
+	{
+  		u = u*x + coef(i);
+	}
+
+ 	return u;
+}
+
+double sqrt(double b)
+{
+ 	double x = 1;
+	int step = 0;
+
+ 	while ((x*x-b<-0.000000000000001 || x*x-b>0.000000000000001) && step<50)
+ 	{
+		x = (b/x+x)/2.0;
+		step++;
+	}
+ 	return x;
+}
+
+double ln(double x)
+{
+	int i;
+
+ 	if (x > 1.5)
+ 	{
+  		for(i=0; x>1.25; i++)
+		{
+   			x = sqrt(x);
+		}
+  		return (1<<i)*horner(x-1);
+ 	}
+ 	else if (x<0.7 && x>0)
+ 	{
+  		for(i=0; x<0.7; i++)
+		{
+   			x = sqrt(x);
+		}
+  		return (1<<i)*horner(x-1);
+ 	}
+ 	else if(x > 0)
+	{
+  		return horner(x-1);
+	}
+}
+
+double exp(double x)
+{
+	double sum = 1;
+ 	int i;
+
+ 	for(i=N; i>0; i--)
+ 	{ 
+	  	sum /= i;
+	  	sum *= x;
+	  	sum += 1;
+ 	}
+ 	return sum;
+}
+
+double pow(double m, double n)
+{
+	return exp(n*ln(m));
+}
+