gfops.h

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/* emacs edit mode for this file is -*- C++ -*- */
 
/**
 * @file gfops.h
 *
 * Operations in GF, where GF is a finite field of size less than 2^16
 * represented by a root of Conway polynomial. Uses look up tables for addition.
 *
 * @sa gf_tabutil.h
**/
#ifndef INCL_GFOPS_H
#define INCL_GFOPS_H
 
// #include "config.h"
 
#ifndef NOSTREAMIO
#ifdef HAVE_IOSTREAM
#include <iostream>
#define OSTREAM std::ostream
#elif defined(HAVE_IOSTREAM_H)
#include <iostream.h>
#define OSTREAM ostream
#endif
#endif /* NOSTREAMIO */
 
#include "cf_assert.h"
 
#include "cf_defs.h"
#include "canonicalform.h"
 
EXTERN_VAR int gf_q;
EXTERN_VAR int gf_p;
EXTERN_VAR int gf_n;
EXTERN_VAR int gf_q1;
EXTERN_VAR int gf_m1;
EXTERN_VAR char gf_name;
 
EXTERN_VAR unsigned short * gf_table;
 
EXTERN_INST_VAR CanonicalForm gf_mipo;
 
//{{{ predicates
inline bool gf_iszero ( int a )
{
    return gf_q == a;
}
 
inline bool gf_iszero ( long a )
{
    return gf_q == a;
}
 
inline bool gf_isone ( int a )
{
    return 0 == a;
}
 
inline bool gf_isone ( long a )
{
    return 0 == a;
}
//}}}
 
//{{{ conversion functions
inline int gf_int2gf ( int i )
{
    while ( i < 0 )
        i += gf_p;
    while ( i >= gf_p )
        i -= gf_p;
    if ( i == 0 )
        return gf_q;
    int c = 0;
    while ( i > 1 ) {
        c = gf_table[c];
        i--;
    }
    return c;
}
 
inline long gf_int2gf ( long i )
{
    while ( i < 0 )
        i += gf_p;
    while ( i >= gf_p )
        i -= gf_p;
    if ( i == 0 )
        return gf_q;
    long c = 0;
    while ( i > 1 ) {
        c = gf_table[c];
        i--;
    }
    return c;
}
//}}}
 
//{{{ zero and one
inline int gf_zero()
{
    return gf_q;
}
 
inline int gf_one()
{
    return 0;
}
//}}}
 
//{{{ inline int gf_sign ( int a )
// docu: see imm_sign()
inline
int gf_sign ( int a )
{
    if ( gf_iszero( a ) )
        return 0;
    else
        return 1;
}
//}}}
 
//{{{ arithmetic operators
inline int gf_neg ( int a )
{
    // -z^a=z^a*(-1)=z^a*gf_m1;
    if ( a == gf_q ) return a;
    int i = a + gf_m1;
    if ( i >= gf_q1 )
        i -= gf_q1;
    return i;
}
 
inline int gf_add ( int a, int b )
{
    // z^a+z^b=z^b*(z^(a-b)+1), if a>=b;
    //        =z^a*(z^(b-a)+1), if a<b;
    if ( a == gf_q ) return b;
    if ( b == gf_q ) return a;
    int zb, zab, r;
    if ( a >= b ) {
        zb = b;
        zab = a - b;
    }
    else {
        zb = a;
        zab = b - a;
    }
    if ( gf_table[zab] == gf_q )
        r = gf_q; /*if z^(a-b)+1 =0*/
    else {
        r= zb + gf_table[zab];
        if ( r >= gf_q1 )
            r -= gf_q1;
    }
    return r;
}
 
inline int gf_sub ( int a, int b )
{
    return gf_add( a, gf_neg( b ) );
}
 
inline int gf_mul ( int a, int b )
{
    if ( a == gf_q || b == gf_q )
        return gf_q;
    else {
        int i = a + b;
        if ( i >= gf_q1 ) i -= gf_q1;
        return i;
    }
}
 
inline long gf_mul ( long a, int b )
{
    if ( a == gf_q || b == gf_q )
        return gf_q;
    else {
        long i = a + b;
        if ( i >= gf_q1 ) i -= gf_q1;
        return i;
    }
}
 
inline int gf_div ( int a, int b )
{
    ASSERT( b != gf_q, "divide by zero" );
    if ( a == gf_q )
        return gf_q;
    else {
        int s = a - b;
        if (s < 0)
            s += gf_q1;
        return s;
    }
}
 
inline int gf_inv ( int a )
{
    ASSERT( a != gf_q, "divide by zero" );
    return gf_q1 - a;
}
//}}}
 
//{{{ input/output
#ifndef NOSTREAMIO
inline void gf_print ( OSTREAM & os, int a )
{
    if ( a == gf_q )
        os << "0";
    else  if ( a == 0 )
        os << "1";
    else  if ( a == 1 )
        os << gf_name;
    else
        os << gf_name << "^" << a;
}
#endif /* NOSTREAMIO */
//}}}
 
//{{{ exponentiation
inline int gf_power ( int a, int n )
{
    if ( n == 0 )
        return 0;
    else if ( n == 1 )
        return a;
    else
        return gf_mul( a, gf_power( a, n-1 ) );
}
 
inline long gf_power ( long a, int n )
{
    if ( n == 0 )
        return 0;
    else if ( n == 1 )
        return a;
    else
        return gf_mul( a, gf_power( a, n-1 ) );
}
//}}}
 
void gf_setcharacteristic ( int p, int n, char name );
 
// Singular needs this
/*BEGINPUBLIC*/
 
long gf_gf2ff ( long a );
int gf_gf2ff ( int a );
 
bool gf_isff ( long a );
bool gf_isff ( int a );
 
/*ENDPUBLIC*/
 
#endif /* ! INCL_GFOPS_H */