An online solution in :

• given a query with X, construct a prefix (from the most significant bit, 29th in this case) of the smallest X^a[i] in the given range: if you know that the smallest k-bit prefix that can be achieved is p, check if it's possible to achieve a k + 1-bit prefix by appending 0 to p; if it isn't possible, you have to append 1 to p

• how to check if the most significant k bits can be equal to p: it's equivalent to checking if p appears in the range [L, R) of an array A[k][i]=a[i]>>(30-k); for each such array, store the positions i on which an element a appears in a map<a,set<i>>, which gives a straighforward way to check

• when you have the smallest b=X^a[i], you just need to count how many times b^X=a[i] appears in that range, which can be done just by augmenting the previous part: for array A[0][], use map<a,map<i,s>> instead, where s gives the number of times a appeared in positions  ≤ i and can be precalculated; then, you just need to find the elements of the inner map<> corresponding to the smallest i  ≥ R,  ≥ L respectively and subtract their s to find the number of occurences of b^X in that range