log ln exp pow的c实现

#include <stdio.h>   
const int N=100;   
  
double coef(int n)   
{   
if(n==0) return 0;   
double t=1.0/n;   
if(n%2==0) t=-t;   
return t;   
}//x^n的系数   
double horner(double x)   
{   
double u=coef(N);   
for(int 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;   
}//开平方   
  
double ln(double x)//ln(1+x)=x-x^2/2+x^3/3-x^4/4……   
{   
if(x>1.5)   
{   
for(int i=0;x>1.25;i++)   
x=sqrt(x);   
return (1<<i)*horner(x-1);   
}   
else if(x<0.7&&x>0)   
{   
for(int i=0;x<0.7;i++)   
x=sqrt(x);   
return (1<<i)*horner(x-1);   
}   
else if(x>0)   
return horner(x-1);   
}   
double log(double m,double base=10)   
{   
return ln(m)/ln(base);//换底公式   
}   
double exp(double x)   
{   
double sum=1;   
for(int i=N;i>0;i--)   
{   
sum/=i;   
sum*=x;   
sum+=1;   
}   
return sum;   
  
}//e^x≈1+x+x^2/2!+x^3/3!+……+x^n/n!   
  
double pow(double m,double n)   
{   
return exp(n*ln(m));   
}   
  
main()   
{   
printf("100^2.5=");printf("%f\n",pow(100,2.5));   
printf("lg(1000)=");printf("%f\n",log(1000));   
}