#include "os.h"#include <mp.h> #define iseven(a)	(((a)->p[0] & 1) == 0) // use extended gcd to find the multiplicative inverse// res = b**-1 mod mvoidmpinvert(mpint *b, mpint *m, mpint *res){	mpint *dc1, *dc2;	// don't care	int r; 	dc1 = mpnew(0);	dc2 = mpnew(0);	mpextendedgcd(b, m, dc1, res, dc2);	r = mpcmp(dc1, mpone);	mpfree(dc1);	mpfree(dc2);	if(r != 0)		sysfatal("mpinvert: no inverse");	mpmod(res, m, res);}