in src/cg21/cg21_pi_mod.c [268:273]
static void boolToChar(const bool arr[][2], char* result) {
for(int i=0; i<CG21_PAILLIER_PROOF_ITERS; i++) {
result[i*2] = arr[i][0] ? '1' : '0';
result[i*2+1] = arr[i][1] ? '1' : '0';
}
}