Improper cosine wave using cordic algorithm?

z1=0:(2*pi/100):2*pi;   y1=zeros(1,length(z1)); x1=ones(1,length(z1))/1.646760255;

c1=zeros(1,length(z1)); CORDIC_SIN=zeros(1,length(z1)); CORDIC_COS=zeros(1,length(z1));
a1=zeros(1,length(z1)); b1=zeros(1,length(z1));
inpLUT=zeros(1,20);
inpLUT(1)=atan(1);
for i=1:1:21
    inpLUT(i+1)=atan(2^-i);
end
n=10;
for i=1:1:length(z1)
    a1=x1(i);
    b1=y1(i);
    c1=z1(i);
   [a1,b1,c1]=cordic_rotation_kernel(a1,b1,c1, inpLUT, n); 
   CORDIC_SIN(i)=b1;
   CORDIC_COS(i)=a1;
end
theta=0:(2*pi/100):2*pi;
sin_out=sin(theta);
cos_out=cos(theta);

Abs_error_sine=abs(CORDIC_SIN-sin_out);
Abs_error_cos=abs(CORDIC_COS-cos_out);
figure(3)
plot(theta,CORDIC_SIN,theta,CORDIC_COS,theta,sin_out,theta,cos_out);
xlabel('Angle (in radians');
ylabel('Amplitude');
legend('Computed cordic sine','Computed cordic cosine','sin out','cos out');

figure(4)
plot(theta,Abs_error_sine,theta,Abs_error_cos);
xlabel('Angle (in radians');
ylabel('Error');
legend('Sine error','Cosine error');

function [x, y, z] = cordic_rotation_kernel(x, y, z,inpLUT, n)
% Perform CORDIC rotation kernel algorithm for N iterations.
xtmp = x;
ytmp = y;
if z > 0 && z <= pi/2
    z=z;
end
if z > pi/2 && z <= pi
    z=pi-z;
end
if z > pi && z <= (3*pi)/2
    z=pi-z;
end
if z > (3*pi)/2 && z <= 2*pi 
    z=z-2*pi;
end
for idx = 1:n
    if z < 0
        z(:) = accumpos(z, inpLUT(idx));
        x(:) = accumpos(x, ytmp);
        y(:) = accumneg(y, xtmp);
    else
        z(:) = accumneg(z, inpLUT(idx));
        x(:) = accumneg(x, ytmp);
        y(:) = accumpos(y, xtmp);
    end
    xtmp = bitsra(x, idx); % bit-shift-right for multiply by 2^(-idx)
    ytmp = bitsra(y, idx); % bit-shift-right for multiply by 2^(-idx)
end
end

Above is the CORDIC function that I have used for creating a sine and a cosine wave. I am trying to compare the inbuilt function with the one that I am attempting to implement. However, from pi to 3*pi , the values of cosine wave tends to be inverted. Kindly do tell me how to rectify this issue?