source: git/Singular/modulop.cc @ 4c001a

/****************************************
*  Computer Algebra System SINGULAR     *
****************************************/
/* $Id: modulop.cc,v 1.7 1997-06-04 19:45:22 obachman Exp $ */
/*
* ABSTRACT: numbers modulo p (<=32003)
*/

#include <limits.h>
#include <string.h>
#include "mod2.h"
#include "tok.h"
#include "febase.h"
#include "mmemory.h"
#include "numbers.h"
#include "longrat.h"
#include "modulop.h"

int npPrimeM=0;
int npGen=0;
int npPminus1M=0;
int npMapPrime;

CARDINAL *npExpTable=NULL;
CARDINAL *npLogTable=NULL;

BOOLEAN npGreaterZero (number k)
{
  int h = (int) k;
  return ((int)h !=0) && (h <= (npPrimeM>>1));
}

number npMult (number a,number b)
{
  if (((int)a == 0) || ((int)b == 0))
    return (number)0;
  else
  {
    return npMultM(a,b);
  }
}

/*2
* create a number from int
*/
number npInit (int i)
{
  while (i <  0)        i += npPrimeM;
  while (i >= npPrimeM) i -= npPrimeM;
  return (number)i;
}

/*2
* convert a number to int (-p/2 .. p/2)
*/
int npInt(number &n)
{
  if ((int)n > (npPrimeM >>1)) return ((int)n -npPrimeM);
  else                     return (int)n;
}

number npCopy (number  k1)
{
  return k1;
}

number npAdd (number a, number b)
{
  int ka = (int)a + (int)b;
  if (ka >= npPrimeM) ka -= npPrimeM;
  return (number)ka;
}

number npSub (number a, number b)
{
//  int ka = (int)a - (int)b;
//  if (ka < 0)  ka += npPrimeM;
//  *(int *)c = ka;
  return npSubM(a,b);
}

BOOLEAN npIsZero (number  a)
{
  return 0 == (int)a;
}

BOOLEAN npIsOne (number a)
{
  return 1 == (int)a;
}

BOOLEAN npIsMOne (number a)
{
  return ((npPminus1M == (int)a)&&(1!=(int)a));
}

number npDiv (number a,number b)
{
  if ((int)a==0)
    return (number)0;
  else if ((int)b==0)
  {
    WerrorS("div by 0");
    return (number)0;
  }
  else
  {
    int s = npLogTable[(int)a] - npLogTable[(int)b];
    if (s < 0)
      s += npPminus1M;
    return (number)npExpTable[s];
  }
}

number  npInvers (number c)
{
  if ((int)c==0)
  {
    WerrorS("1/0");
    return (number)0;
  }
  return (number)npExpTable[npPminus1M - npLogTable[(int)c]];
}

number npNeg (number c)
{
//  *(int *)c = npPrimeM-*(int *)c;
  return npNegM(c);
}

BOOLEAN npGreater (number a,number b)
{
  return (int)a != (int)b;
}

BOOLEAN npEqual (number a,number b)
{
//  return (int)a == (int)b;
  return npEqualM(a,b);
}

void npWrite (number &a)
{
  if ((int)a > (npPrimeM >>1)) StringAppend("-%d",npPrimeM-((int)a));
  else                     StringAppend("%d",(int)a);
}

void npPower (number a, int i, number * result)
{
  if (i==0)
  {
    //npInit(1,result);
    *(int *)result = 1;
  }
  else if (i==1)
  {
    //*result = npCopy(a);
    *result = a;
  }
  else
  {
    npPower(a,i-1,result);
    *result = npMultM(a,*result);
  }
}

char* npEati(char *s, int *i)
{

  if (((*s) >= '0') && ((*s) <= '9'))
  {
    (*i) = 0;
    do
    {
      (*i) *= 10;
      (*i) += *s++ - '0';
      if ((*i) >= (INT_MAX / 10)) (*i) = (*i) % npPrimeM;
    }
    while (((*s) >= '0') && ((*s) <= '9'));
    if ((*i) >= npPrimeM) (*i) = (*i) % npPrimeM;
  }
  else (*i) = 1;
  return s;
}

char * npRead (char *s, number *a)
{
  int z;
  int n=1;

  s = npEati(s, &z);
  if ((*s) == '/')
  {
    s++;
    s = npEati(s, &n);
  }
  *a = npDiv((number)z,(number)n);
  return s;
}

/*2
* the last used charcteristic
*/
//int npGetChar()
//{
//  return npPrimeM;
//}

/*2
* set the charcteristic (allocate and init tables)
*/

void npSetChar(int c)
{
  int i, w;

  if (c==npPrimeM) return;
  if (npPrimeM > 1)
  {
    Free( (ADDRESS)npExpTable,npPrimeM*sizeof(CARDINAL) );
    Free( (ADDRESS)npLogTable,npPrimeM*sizeof(CARDINAL) );
    npExpTable=NULL;
    npLogTable=NULL;
  }
  if ((c>1) || (c<(-1)))
  {
    if (c>1) npPrimeM = c;
    else     npPrimeM = -c;
    npPminus1M = npPrimeM - 1;
    npExpTable= (CARDINAL *)Alloc( npPrimeM*sizeof(CARDINAL) );
    npLogTable= (CARDINAL *)Alloc( npPrimeM*sizeof(CARDINAL) );
    npExpTable[0] = 1;
    npLogTable[1] = 0;
    if (npPrimeM > 2)
    {
      w = 1;
      loop
      {
        npLogTable[1] = 0;
        w++;
        i = 0;
        loop
        {
          i++;
          npExpTable[i] = (int)(((long)w * (long)npExpTable[i-1]) % npPrimeM);
          npLogTable[npExpTable[i]] = i;
          if (/*(i == npPrimeM - 1 ) ||*/ (npExpTable[i] == 1))
            break;
        }
        if (i == npPrimeM - 1)
          break;
      }
    }
    else
    {
      npExpTable[1] = 1;
    }
  }
  else
    npPrimeM=0;
 npGen=w;
}


#ifdef LDEBUG
BOOLEAN npDBTest (number a, char *f, int l)
{
  if (((int)a<0) || ((int)a>npPrimeM))
  {
    return FALSE;
  }
  return TRUE;
}
#endif

number npMap0(number from)
{
  return npInit(nlModP(from,npPrimeM));
}

number npMapP(number from)
{
  int i = (int)from;
  if (i>npMapPrime/2)
  {
    i-=npMapPrime;
    while (i < 0) i+=npPrimeM;
  }
  i%=npPrimeM;
  return (number)i;
}

BOOLEAN npSetMap(int c, char ** par, int nop, number minpol)
{
  if (c == 0)
  {
    nMap = npMap0;   /*Q -> Z/p*/
    return TRUE;
  }
  if (c == npPrimeM)
  {
    nMap = npCopy;  /* Z/p -> Z/p*/
    return TRUE;
  }
  if (c>1)
  {
    if (par==NULL)
    {
      npMapPrime=c;
      nMap = npMapP; /* Z/p' -> Z/p */
      return TRUE;
    }
    else
    {
      return FALSE;   /* GF(q) ->Z/p */
    }
  }
  if (c<0)
  {
    return FALSE;   /* Z/p'(a) -> Z/p*/
  }
  if (c==1)
  {
    return FALSE;   /* Q(a) -> Z/p */
  }
  return FALSE;      /* default */
}

/*2
* dummy modulus: return 0
*/
number npIntMod(number a, number b)
{
  return (number)0;
}