#include "transfer.h"
#include <math.h>
#define CHECK_BIT(val, pos) ((1 << pos) & val)
using namespace std;
vector<int> get_attachment(vector<int> source) {
int N = source.size();
int M = ceil(log2(N));
vector<int> extra(M, 0);
for (int i = 1; i < N; i++) {
for (int j = 0; j < M; j++) {
if (CHECK_BIT(i, j))
extra[j] ^= source[i];
}
}
for (int j = 0; j < M; j++) {
extra[j] ^= source[0];
}
int xorextra = 0;
for (int i = 0; i < M; i++)
xorextra ^= extra[i];
extra.push_back(xorextra);
return extra;
}
vector<int> retrieve(vector<int> data) {
vector<int> source;
vector<int> extras;
int xorextra = data.back();
data.pop_back();
int N = 1;
while (N + ceil(log2(N)) < data.size()) {
N++;
}
int M = 0;
M = ceil(log2(N));
source = vector<int>(data.begin(), data.begin() + N);
extras = vector<int>(data.begin() + N, data.end());
int xorsum = 0;
for (int i = 0; i < M; i++)
xorsum ^= extras[i];
if (xorsum != xorextra) {
return source;
}
vector<int> cur_sum(M, 0);
for (int i = 1; i < N; i++) {
for (int j = 0; j < M; j++) {
if (CHECK_BIT(i, j))
cur_sum[j] ^= source[i];
}
}
for (int j = 0; j < M; j++)
cur_sum[j] ^= source[0];
int pos = 0;
for (int j = 0; j < M; j++) {
if (extras[j] != cur_sum[j])
pos += 1 << j;
}
if (pos) {
if (pos == (1 << M) - 1)
source[0] ^= 1;
else
source[pos] ^= 1;
}
return source;
}
