sqrtf.c

这个函数是一段采用二分法计算正的浮点数开方的代码

/*采用二分法实现的求开平方的函数sqrtf()*/
float sqrtf(float x){
  //int x1,x2,x3;
  float x1,x2,x3,y,fx;
  float fx1,fx2,fx3,fx4;//printf("sqrtf() test 1\n");
  if(x<0) printf("x<0,No Root Value!");
  else if(x==0) y=x;
  else{
    x1=0;x2=0;
    do
     { x2=x2+0.5;//printf("in sqrtf() x2=%d\n",(int)x2);
       fx2=x2*x2-x;//printf("in sqrtf() fx2=%d\n",(int)(fx2));printf("sqrtf() test 2\n");
     }while(fx2<0);

   if(fx2==0) y=x2;
   else
     { x1=x2-0.5;
       do
       { x3=(x1+x2)/2;
         fx1=x1*x1-x;  //printf("sqrtf() test 3 fx1=%d\n",(int)(-(1000*fx1)));
         fx3=x3*x3-x; //printf("sqrtf() test 4\n");
         if(fx1*fx3>0) x1=x3;         /*fx1与fx3同符号,则根值处于x3~x2之间*/
         if(fx1*fx3<0) x2=x3;         /*fx1与fx3符号相反,则根值处于x1~x3之间*/
         if(fx3==0)   break;
        if(fx3>=0) fx4=fx3;
         else fx4=-fx3;
       }while(fx4>0.005);//printf("sqrtf() test 3 fx4=%d\n",(int)(1000*fx4));
       y=x3;
     }
  }
  return(y);
 }