asn1_primitives_getters.h

/*
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Copyright (c) 2023-2024 Institute for Automotive Engineering (ika), RWTH Aachen University
 
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*/
 
#ifndef ETSI_ITS_MSGS_UTILS_IMPL_ASN1_PRIMITIVES_ASN1_PRIMITIVES_GETTERS_H
#define ETSI_ITS_MSGS_UTILS_IMPL_ASN1_PRIMITIVES_ASN1_PRIMITIVES_GETTERS_H


inline std::vector<bool> getBitString(const std::vector<uint8_t>& buffer, const int bits_unused) {
  // bit string size
  const int bits_per_byte = 8;
  const int n_bytes = buffer.size();
  const int n_bits = n_bytes * bits_per_byte;
  std::vector<bool> bits;
  bits.resize(n_bits - bits_unused, 0);
 
  // loop over bytes in reverse order
  for (int byte_idx = n_bytes - 1; byte_idx >= 0; byte_idx--) {
      // loop over bits in a byte
      for (int bit_idx_in_byte = bits_per_byte - 1; bit_idx_in_byte >= 0; bit_idx_in_byte--) {
        
        // map bit index in byte to bit index in total bitstring
        int bit_idx = (n_bytes - byte_idx - 1) * bits_per_byte + bit_idx_in_byte;
        if (byte_idx == 0 && bit_idx < bits_unused) break;
 
        // extract bit from bitstring and set output array entry appropriately
        bool byte_has_true_bit = buffer[byte_idx] & (1 << bit_idx_in_byte);
        if (byte_has_true_bit) bits[bits_per_byte-bit_idx-1] = true;
      }
    }
  return bits;
}
 
#endif  // ETSI_ITS_MSGS_UTILS_IMPL_ASN1_PRIMITIVES_GETTERS_H