平方总是求幂法

Question

besides the square-and-multiply method, there is this method square-and-multiply-always, and i am trying to implement it in python. My problem is that during searching i found a pseudocode for it, here and i implemented it in python but it does not yield the correct results in comparison to pow function.
The pseudo code can be found in the link above or in this screenshot .

My implementation is

def square_and_multiply_always(base, exp, mod):
    R0=1
    R1 = base
    c = '{0:b}'.format(exp)
    i=len(c)
    t=0
    while i>=0:
        if(t==0):
            Rt=R0
        elif(t==1):
            Rt=R1
        else:
             print("t != 0 or 1")
        R0=(R0*Rt)%mod
        a=int(c[i-1])
        t=(t^a)
        i=i-1+t
    return R0

Answer 1

i managed to find my mistakes so here is a proper code for future searches that end up here

def square_and_multiply_always(base, exp, mod):
    R0=1
    R1 = base
    c = '{0:b}'.format(exp)
    i=len(c)-1
    t=0
    c=c[::-1]
    while(i>=0):
        if(t==0):
            Rt=R0
        elif(t==1):
            Rt=R1
        else:
            print("t != 0 or 1")
        R0=(R0*Rt)%mod
        d=int(c[i])
        t=(t^d)
        i=i-1+t
    return R0