/**************************************************************************\

MODULE: GF2

SUMMARY:

The class GF2 represents the field GF(2).
Computationally speaking, it is not a particularly useful class.
Its main use is to make the interfaces to the various finite 
field classes as uniform as possible.

\**************************************************************************/

#include <NTL/ZZ.h>


class GF2 {
public:
   
   GF2(); // initial value 0

   GF2(const GF2& a); // copy constructor

   GF2& operator=(const GF2& a); // assignment
   GF2& operator=(long a); // assignment

};


long rep(GF2 a); // read-only access to representation of a





/**************************************************************************\

                                  Comparison

\**************************************************************************/


long operator==(GF2 a, GF2 b);
long operator!=(GF2 a, GF2 b);

long IsZero(GF2 a);  // test for 0
long IsOne(GF2 a);  // test for 1

// PROMOTIONS: operators ==, != promote long to GF2 on (a, b).


/**************************************************************************\

                                    Addition 

\**************************************************************************/

// operator notation:

GF2 operator+(GF2 a, GF2 b);
GF2 operator-(GF2 a, GF2 b);

GF2 operator-(GF2 a); // unary -

GF2& operator+=(GF2& x, GF2 a);
GF2& operator+=(GF2& x, long a);

GF2& operator-=(GF2& x, GF2 a);
GF2& operator-=(GF2& x, long a);

GF2& operator++(GF2& x);  // prefix
void operator++(GF2& x, int);  // postfix

GF2& operator--(GF2& x);  // prefix
void operator--(GF2& x, int);  // postfix

// procedural versions:


void add(GF2& x, GF2 a, GF2 b); // x = a + b
void sub(GF2& x, GF2 a, GF2 b); // x = a - b 
void negate(GF2& x, GF2 a); // x = -a

// PROMOTIONS: binary +, -, and procedures add, sub promote
// from long to GF2 on (a, b).


/**************************************************************************\

                                  Multiplication 

\**************************************************************************/

// operator notation:

GF2 operator*(GF2 a, GF2 b);

GF2& operator*=(GF2& x, GF2 a);
GF2& operator*=(GF2& x, long a);

// procedural versions:

void mul(GF2& x, GF2 a, GF2 b); // x = a * b

void sqr(GF2& x, GF2 a); // x = a^2
GF2 sqr(GF2 a); 

// PROMOTIONS: operator * and procedure mul promote from long to GF2
// on (a, b).


/**************************************************************************\

                                  Division

\**************************************************************************/

operator notation:

GF2 operator/(z_p a, GF2 b);

GF2& operator/=(GF2& x, GF2 a);
GF2& operator/=(GF2& x, long a);

procedural versions:

void div(GF2& x, GF2 a, GF2 b);
// x = a/b

void inv(GF2& x, GF2 a);
GF2 inv(GF2 a);
// x = 1/a

// PROMOTIONS: operator / and procedure div promote from long to GF2
// on (a, b).


/**************************************************************************\

                                  Exponentiation

\**************************************************************************/


void power(GF2& x, GF2 a, long e); // x = a^e (e may be negative)
GF2 power(GF2 a, long e); 


/**************************************************************************\

                               Random Elements

\**************************************************************************/


void random(GF2& x);
GF2 random_GF2();
// x = random element in GF2.  Uses RandomBnd from ZZ.


/**************************************************************************\

                                Input/Output

\**************************************************************************/


ostream& operator<<(ostream& s, GF2 a);

istream& operator>>(istream& s, GF2& x);
// a ZZ is read and reduced mod 2


/**************************************************************************\

                               Miscellany

\**************************************************************************/


void clear(GF2& x); // x = 0
void set(GF2& x); // x = 1

void swap(GF2& x, GF2& y);
// swap x and y 

static GF2 GF2::zero();
// GF2::zero() yields a read-only reference to zero

static long GF2::modulus();
// GF2::modulus() returns the value 2