Simulate reverse process of the xxd command

reverse_xxd.cpp

/**
 * Program: Simulate reverse xxd (to convert hex dump to binary RAW file)
 * Author: Abhishek Bhattacharya
 */

#include <bits/stdc++.h>
using namespace std;

unsigned int make_4_bit_binary(char &ch) {
	unsigned int hexval;

	if(ch >= '0' && ch <= '9')
		hexval = ch - '0';
	else {
		hexval = ch - 'a' + 10;
	}

	return hexval & 0xff;
}

int main(int argc, char *argv[]) {
	if(argc >= 2 && string(argv[1]) == "--help") {
		cout << "HELP:" << endl
		<< "\n<executable_file_name> [--help] hexdump_file_name binary_destination_file_name" << endl
		<< "\nNOTE: The hexdump_file should be of a specific format. The right format is achieved using:" << endl
		<< "\n$>  xxd -p source_binary_file_name > hexdump_file_name\n" << endl;
	} else if(argc < 3) {
		cout << "ERROR: Too few arguments passed. Are you sure you passed the name of the FILEs?" << endl;
		return 0;
	}

	string buff;
	ifstream fin(argv[1]);
	ofstream fout(argv[2], ios::out|ios::binary);
	unsigned int out1, out2;
	char outc;

	if(fin.is_open() && fout.is_open()) {
		while(getline(fin, buff)) {
			for(size_t i = 0; i<buff.size(); i+=2) {
				// accumulate 8 bits of data

				// check if full 8 bits of data not available
				if(i == buff.size()-1)
					out2 = 0x00;
				else
					out2 = make_4_bit_binary(buff[i+1]);

				out1 = make_4_bit_binary(buff[i]);

				outc = (out1 << 4) + (out2 & 0x0f);

				// debug
				// cout << buff[i] << ((i == buff.size()-1) ? '0' : buff[i+1]) << " => " << out1 << " " << out2 << " -> " << outc << endl;

				// write binary 8-bit block
				fout.write(&outc, sizeof(outc));
			}
		}
		// fin.close();
		// fout.close();
	} else
		  cout << "ERROR: FILE " << argv[1] << " and/or " << argv[2] << " could not be opened. \
      Check the files and try again." << endl;

	return 0;
}

reverse_xxd.md

Reverse xxd

A simple experiment to simulate the reverse effect of the xxd command. Converts a raw hexdump made with xxd back to a RAW binary file.

Usage

Compile as C++98 or above.

<executable_file_name> [--help] hexdump_file_name binary_destination_file_name

Example usage:

xxd -p sample.jpg test.hex
reverse_xxd test.hex sample_copy.jpg

License

Distributed under the MIT License.