c语言实现sin,cos,sqrt,pow函数

float abs(float x) 
{
    if(x<0) x=0-x;
    return x;
}


float sin(float x) 

{

 const float B = 1.2732395447; 
 const float C = -0.4052847346;
 const float P = 0.2310792853;//0.225; 
 float y = B * x + C * x * abs(x);
 y = P * (y * abs(y) - y) + y;
 return y;
 }


float cos(float x) 
{
  const float Q = 1.5707963268;
  const float PI =3.1415926536;
  x += Q; 

  if(x > PI) 
    x -= 2 * PI; 

 return( sin(x));
}


float sqrt(float a)
 {
   double x,y;
   x=0.0;
   y=a/2;
   while(x!=y)
   {
     x=y;
     y=(x+a/x)/2;
   }
   return x;
 }


float pow(float a,int b)
{
    float r=a;
    if(b>0)
    {
      while(--b)
         r*=a;

    }
    else if(b<0)
    {
        while(++b)     r*=a;
         r=1.0/r;
    }
    else r=0;
    return r;
}