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/*************************************************************************/
/* Copyright (c) 2015 dx, http://kaimi.ru */
/* */
/* Permission is hereby granted, free of charge, to any person */
/* obtaining a copy of this software and associated documentation */
/* files (the "Software"), to deal in the Software without */
/* restriction, including without limitation the rights to use, */
/* copy, modify, merge, publish, distribute, sublicense, and/or */
/* sell copies of the Software, and to permit persons to whom the */
/* Software is furnished to do so, subject to the following conditions: */
/* The above copyright notice and this permission notice shall be */
/* included in all copies or substantial portions of the Software. */
/* */
/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, */
/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF */
/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY */
/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, */
/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE */
/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. */
/*************************************************************************/
#include "pe_checksum.h"
#include "pe_structures.h"
#include "pe_base.h"
namespace pe_bliss
{
using namespace pe_win;
//Calculate checksum of image
uint32_t calculate_checksum(std::istream& file)
{
//Save istream state
std::ios_base::iostate state = file.exceptions();
std::streamoff old_offset = file.tellg();
//Checksum value
unsigned long long checksum = 0;
try
{
image_dos_header header;
file.exceptions(std::ios::goodbit);
//Read DOS header
pe_base::read_dos_header(file, header);
//Calculate PE checksum
file.seekg(0);
unsigned long long top = 0xFFFFFFFF;
top++;
//"CheckSum" field position in optional PE headers - it's always 64 for PE and PE+
static const unsigned long checksum_pos_in_optional_headers = 64;
//Calculate real PE headers "CheckSum" field position
//Sum is safe here
unsigned long pe_checksum_pos = header.e_lfanew + sizeof(image_file_header) + sizeof(uint32_t) + checksum_pos_in_optional_headers;
//Calculate checksum for each byte of file
std::streamoff filesize = pe_utils::get_file_size(file);
for(long long i = 0; i < filesize; i += 4)
{
unsigned long dw = 0;
//Read DWORD from file
file.read(reinterpret_cast<char*>(&dw), sizeof(unsigned long));
//Skip "CheckSum" DWORD
if(i == pe_checksum_pos)
continue;
//Calculate checksum
checksum = (checksum & 0xffffffff) + dw + (checksum >> 32);
if(checksum > top)
checksum = (checksum & 0xffffffff) + (checksum >> 32);
}
//Finish checksum
checksum = (checksum & 0xffff) + (checksum >> 16);
checksum = (checksum) + (checksum >> 16);
checksum = checksum & 0xffff;
checksum += static_cast<unsigned long>(filesize);
}
catch(const std::exception&)
{
//If something went wrong, restore istream state
file.exceptions(state);
file.seekg(old_offset);
file.clear();
//Rethrow
throw;
}
//Restore istream state
file.exceptions(state);
file.seekg(old_offset);
file.clear();
//Return checksum
return static_cast<uint32_t>(checksum);
}
}
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