#include "transfer.h"
using namespace std;
#include <cstdio>
#include <cassert>
std::vector<int> get_attachment(std::vector<int> source) {
int N = source.size();
assert(N == 63 || N == 255);
source.push_back(0);
++N;
vector<int> res;
for (int len = N/2; len > 0; len /= 2) {
int bit = 0;
for (int start = 0; start < N; start += len*2) {
for (int i = 0; i < len; ++i)
bit ^= source[start + i];
}
res.push_back(bit);
}
int tbit = 0;
for (int x : res)
tbit ^= x;
res.push_back(tbit);
/*
for (int x : res)
fprintf(stderr, "%d", x);
fprintf(stderr, "\n");
*/
return res;
}
std::vector<int> retrieve(std::vector<int> data) {
assert(data.size() == 63 + 7 || data.size() == 255 + 9);
int N, K;
if (data.size() == 63+7)
N = 63, K = 7;
else
N = 255, K = 9;
vector<int> checkbits(data.begin()+N, data.end());
data.erase(data.begin()+N, data.end());
/*
fprintf(stderr, "data:");
for (int x : data)
fprintf(stderr, "%d", x);
fprintf(stderr, "\n");
fprintf(stderr, "checkbits:");
for (int x : checkbits)
fprintf(stderr, "%d", x);
fprintf(stderr, "\n");
*/
assert((int) data.size() == N);
assert((int) checkbits.size() == K);
int last_bit = checkbits.back();
checkbits.pop_back();
--K;
// check bit on trailer info:
int tbit = 0;
for (int k = 0; k < K; ++k)
tbit ^= checkbits[k];
if (tbit != last_bit)
return data;
int L = 0, R = N;
++N;
for (int k = 0, len = N/2; len > 0; ++k, len /= 2) {
assert(k < K);
int bit = 0;
for (int start = 0; start < N; start += len*2) {
for (int i = 0; i < len; ++i)
bit ^= data[start + i];
}
// fprintf(stderr, "k:%d len:%d L:%d R:%d bit:%d checkbit:%d\n",
// k, len, L, R, bit, checkbits[k]);
int mid = (L + R) / 2;
if (bit != checkbits[k]) {
R = mid;
}
else {
L = mid+1;
}
}
// fprintf(stderr, "L: %d R: %d\n", L, R);
assert(L == R);
if (L < (int) data.size())
data[L] ^= 1;
return data;
}
