Fast power recursion

#1

When we are doing normal recursion we are multiplying
a* power(a,n-1)
but when we are doing fast power rescursion
we are not multiplying a, we are directly calculating power(a,n/2). Why?

#2

We are multiplying a with small_pow when n is only odd, for even value of n we don’t need to do that. as we are returning square of small_pow and in it we are calculating a^(n/2).

For odd: 
          return a*small_pow(a,n/2)*small_pow(a,n/2)
For even:
          return small_pow(a,n/2)*small_pow(a,n/2)
#3

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