java math.log的实现

java源代码中的log函数 ，没有具体的实现方法，我在网上找到的c 的实现方法,改了一小下。 



package com.program;

public class LogTest {
public static void main(String[] args) {

System.out.println(new LogTest().logTest(100, 10));
}
static int N = 100;

public  double logTest(double m, double base) {
return in(m) / in(base);
}

public double in(double x)// ln(1+x)=x-x^2/2+x^3/3-x^4/4……
{
if (x > 1.5) {
int i;
for (i = 0; x > 1.25; i++) {
x = Math.sqrt(x);
}
return (1 << i) * horner(x - 1);
} else if (x < 0.7 && x > 0) {
int i;
for ( i = 0; x < 0.7; i++) {
x = Math.sqrt(x);
}
return (1 << i) * horner(x - 1);
} else if (x > 0)
return horner(x - 1);

return 0.0;

}

double horner(double x) {
double u = coef(N);
for (int i = N - 1; i >= 0; i--)
u = u * x + coef(i);
return u;
}

double coef(int n) {
if (n == 0)
return 0;
double t = 1.0 / n;
if (n % 2 == 0)
t = -t;
return t;
}
}