单片机ASCII码转Double计算精度达不到要求怎么搞程序写的。该怎么改？求大神指导 -

double ASCII_to_D_Double(uchar *in_sp,uchar in_num)
{
double xdata a=0;
double xdata b;
uchar xdata j,i,k;
uchar xdata buf[8];
for(i=0;i<in_num;i++)
if(in_sp[i]=='.')break;
for(j=i+1;j<in_num;j++)buf[j-i-1]=in_sp[j]-0x30;
k=in_num-i-1;
if(k==8){b=buf[0]*0.1;b+=buf[1]*0.01;b+=buf[2]*0.001;b+=buf[3]*0.0001;b+=buf[4]*0.00001;b+=buf[5]*0.000001;b+=buf[6]*0.0000001;b+=buf[7]*0.00000001;}
else if(k==7){b=buf[0]*0.1;b+=buf[1]*0.01;b+=buf[2]*0.001;b+=buf[3]*0.0001;b+=buf[4]*0.00001;b+=buf[5]*0.000001;b+=buf[6]*0.0000001;}
else if(k==6){b=buf[0]*0.1;b+=buf[1]*0.01;b+=buf[2]*0.001;b+=buf[3]*0.0001;b+=buf[4]*0.00001;b+=buf[5]*0.000001;}
else if(k==5){b=buf[0]*0.1;b+=buf[1]*0.01;b+=buf[2]*0.001;b+=buf[3]*0.0001;b+=buf[4]*0.00001;}
else if(k==4){b=buf[0]*0.1;b+=buf[1]*0.01;b+=buf[2]*0.001;b+=buf[3]*0.0001;}
else if(k==3){b=buf[0]*0.1;b+=buf[1]*0.01;b+=buf[2]*0.001;}
else if(k==2){b=buf[0]*0.1;b+=buf[1]*0.01;}
else if(k==1){b=buf[0]*0.1;}
k=(in_sp[i-2]-0x30)*10+in_sp[i-1]-0x30;
b=k+b;
b=b/60;
if(i==5){k=in_sp[0]-0x30;k*=100;k+=(in_sp[1]-0x30)*10;k+=in_sp[2]-0x30;}
else if(i==4){k=in_sp[0]-0x30;k*=10;k+=(in_sp[1]-0x30);}
else if(i==3){k=in_sp[0]-0x30;}
a=b+k;
return a;
}

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