text: /*
   * Copyright (c) 2017, Matias Fontanini
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions are
   * met:
   * 
   * * Redistributions of source code must retain the above copyright
   *   notice, this list of conditions and the following disclaimer.
   * * Redistributions in binary form must reproduce the above
   *   copyright notice, this list of conditions and the following disclaimer
   *   in the documentation and/or other materials provided with the
   *   distribution.
   * 
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
   * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
   * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
   * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
   * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
   * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   *
   */
  
  #include <tins/utils/checksum_utils.h>
  #include <cstring>
  #include <tins/ip_address.h>
  #include <tins/ipv6_address.h>
  #include <tins/endianness.h>
  #include <tins/memory_helpers.h>
  
  using std::memcpy;
  
  using Tins::Memory::InputMemoryStream;
  using Tins::Memory::OutputMemoryStream;
  
  namespace Tins {
  namespace Utils {
  
  uint32_t do_checksum(const uint8_t* start, const uint8_t* end) {
      return Endian::host_to_be<uint32_t>(sum_range(start, end));
  }
  
  uint16_t sum_range(const uint8_t* start, const uint8_t* end) {
      uint32_t checksum(0);
      const uint8_t* last = end;
      uint16_t buffer = 0;
      uint16_t padding = 0;
      const uint8_t* ptr = start;
  
      if (((end - start) & 1) == 1) {
          last = end - 1;
          padding = Endian::host_to_le<uint16_t>(*(end - 1));
      }
  
      while (ptr < last) {
          memcpy(&buffer, ptr, sizeof(uint16_t));
          checksum += buffer;
          ptr += sizeof(uint16_t);
      }
  
      checksum += padding;
      
      return fold_sum(checksum);
  }
  
  uint16_t fold_sum(uint32_t sum) {
      while (sum >> 16) {
          sum = (sum & 0xffff) + (sum >> 16);
      }
      
      return static_cast<uint16_t>(sum);
  }
  
  template <size_t buffer_size, typename AddressType>
  uint32_t generic_pseudoheader_checksum(const AddressType& source_ip, 
                                         const AddressType& dest_ip,
                                         uint16_t len,
                                         uint16_t flag) {
      uint8_t buffer[buffer_size];
      OutputMemoryStream stream(buffer, sizeof(buffer));
      stream.write(source_ip);
      stream.write(dest_ip);
      stream.write(Endian::host_to_be(flag));
      stream.write(Endian::host_to_be(len));
  
      InputMemoryStream input_stream(buffer, sizeof(buffer));
      uint32_t checksum = 0;
      while (input_stream) {
          checksum += input_stream.read<uint16_t>();
      }
      return checksum;
  }
  
  uint32_t pseudoheader_checksum(IPv4Address source_ip, 
                                 IPv4Address dest_ip,
                                 uint16_t len,
                                 uint16_t flag) {
      return generic_pseudoheader_checksum<sizeof(uint32_t) * 3>(
          source_ip, dest_ip, len, flag
      );
  }
  
  uint32_t pseudoheader_checksum(IPv6Address source_ip,
                                 IPv6Address dest_ip,
                                 uint16_t len,
                                 uint16_t flag) {
      return generic_pseudoheader_checksum<IPv6Address::address_size * 2 + sizeof(uint16_t) * 2>(
          source_ip, dest_ip, len, flag
      );
  }
  
  uint32_t crc32(const uint8_t* data, uint32_t data_size) {
      uint32_t i, crc = 0;
      static uint32_t crc_table[] = {
          0x4DBDF21C, 0x500AE278, 0x76D3D2D4, 0x6B64C2B0,
          0x3B61B38C, 0x26D6A3E8, 0x000F9344, 0x1DB88320,
          0xA005713C, 0xBDB26158, 0x9B6B51F4, 0x86DC4190,
          0xD6D930AC, 0xCB6E20C8, 0xEDB71064, 0xF0000000
      };
  
      for (i = 0; i < data_size; ++i) {
          crc = (crc >> 4) ^ crc_table[(crc ^ data[i]) & 0x0F];
          crc = (crc >> 4) ^ crc_table[(crc ^ (data[i] >> 4)) & 0x0F];
      }
  
      return crc;
  }
  
  
  } // Utils
  } // Tins
  