// differ.cpp//// C++ code by Kevin Harmon and Leonid Reyzin//// Finds the symmetric difference of two sets given their // PinSketch BCH-based secure sketches,// or given the sketch of the first set// and the entire second set.//// See pinsketch.txt for detailed documentation//#include "pinsketch.h"int main(int argc, char** argv){	int len1, len2; // lengths of argv[1], argv[2], if they exist	long d; // minimum distance of the code;                 // can handle set difference up to t=(d-1)/2 elements		// sketches are (d-1)/2 elements long	long d1, d2;        long m; // elements of the set and of the sketch are m-bit values	GF2X irrP; // irreducible polynomial generating GF(2^m)	vec_GF2E ss1; // sketch of the first set	vec_GF2E ss2; // sketch of the second set	vec_GF2E ss; // sketch of the set difference	bool success;	if (argc != 3 || 	    (len1=strlen(argv[1])) < 4 || (len2=strlen(argv[2])) < 4 ||	    strcmp(&argv[1][len1-3], ".ss") ||	    (strcmp(&argv[2][len2-3], ".ss") && strcmp (&argv[2][len2-4], ".set")))	{			cerr << "Usage:\ndiffer A.ss B.ss\nOR\ndiffer A.ss B.set\n";		if (argc == 3)			cerr << "(first file must be named `*.ss`, second can be either `*.ss' or `*.set')" << endl;		return -1;	}			bool mode; // 0 if comparing .ss with .ss; 1 if comparing .ss with .set	mode = (strcmp (&argv[2][len2-4], ".set")==0);	ifstream infile1(argv[1]);	ifstream infile2(argv[2]);        if (!infile1 || !infile2) {           cerr << "Could not open files!" << endl;           if (infile1) infile1.close();           if (infile2) infile2.close();           return -1;        }	// fix field and error tolerance	ReadSSParams(m, d1, irrP, infile1);	if (!mode) { // the second input is .ss, i.e., another secure sketch        	long m2;		GF2X irrP2;		ReadSSParams(m2, d2, irrP2, infile2);		// We cannot work with the two sketches unless		// they were computed over the same field		// If error-tolerance is not the same, that's ok, we will work with the smaller		// of the two		if (m != m2 || irrP != irrP2)		{		  cerr << "Incompatible parameters!" << endl;		  infile1.close();		  infile2.close();		  return -1;		}	}	// Initialize the field	GF2E::init(irrP);	// read in first syndrome	ReadSS(ss1, infile1, d1);	infile1.close();	if (!mode) { // the second input is .ss, i.e., another secure sketch		// read in second syndrome	        ReadSS(ss2, infile2, d2);		// chop the syndromes to the smaller of the two		d = min(d1, d2);		ss1.SetLength((d-1)/2);		ss2.SetLength((d-1)/2);	}	else { // the second input is a .set file, i.e., a set	      // params are ignored in .set case and are taken from the .ss file		long m2;		ReadSetParams(m2, d2, infile2); 		d = d1;		// compute second syndrome		vec_GF2E set;		ReadSet(set, infile2, m);		BCHSyndromeCompute(ss2, set, d);	}	infile2.close();        // Compute the syndrome of the set difference	// By linearity, it is the same as the difference of the syndromes	// of the two sets	ss = ss1 - ss2;	vec_GF2E setDifference;	// Find the set difference from its syndrome	// This is the most difficult and interesting part	success = BCHSyndromeDecode(setDifference, ss, d);	if (success == false) { 		cerr << "Set difference too large, greater than " 		        << (d-1)/2 << " elements.\n"		        << "Unable to compute from the given sketches.\n";		return -1;	}	OutputSetDifference(cout, setDifference);	return 0;}