#include "transfer.h"
std::vector<int> get_attachment(std::vector<int> source)
{
unsigned const lgn = 32 - __builtin_clz(source.size());
std::vector<int> y(lgn + 1, 0);
int x = 0;
for (unsigned i = 1; i <= source.size(); i++)
{
y[0] ^= source[i - 1];
x ^= source[i - 1] * i;
}
for (unsigned i = 1; i <= lgn; i++)
y[i] = (x >> (lgn - i)) & 1;
return y;
}
std::vector<int> retrieve(std::vector<int> data)
{
unsigned const lgn = 31 - __builtin_clz(data.size());
unsigned const n = 1 << lgn;
int p = 0, x = 0;
for (unsigned i = 1; i <= n - 1; i++)
{
p ^= data[i - 1];
x ^= data[i - 1] * i;
}
if (p == data[n - 1])
return std::vector<int>(data.begin(), data.begin() + n - 1);
int y = 0;
for (unsigned i = 0; i < lgn; i++)
y = (y << 1) | data[n + i];
if (y != x)
data[(y ^ x) - 1] ^= 1;
return std::vector<int>(data.begin(), data.begin() + n - 1);
}
