Length of a Line Without Square Root

int length(int x,int y)
//average error of about 4%
{
    if(abs(x)>abs(y))
        return abs(x)+(abs(y)>>1);
    else
        return abs(y)+(abs(x)>>1);
}

float length(float x,float y)
//average error of about 0.005%
//similar error as the 'rounding error' of 32bit floating point)
{
    float a,b;
    if(abs(x)>abs(y))
    {
        a=abs(x);
        b=abs(y);
    }
    else
    {
        b=abs(x);
        a=abs(y);
    }
    a=a+0.42f*b*b/a;
    return (a+(x*x+y*y)/a)/2;
}

int length3d(int x, int y, int z)
{
    return length(length(x,y),z);
}
float length3d(float x, float y, float z)
{
    return length(length(x,y),z);
}