/* mpz_kronecker_ui -- Kronecker/Jacobi symbol. */

/*
Copyright (C) 1999, 2000 Free Software Foundation, Inc.

This file is part of the GNU MP Library.

The GNU MP Library is free software; you can redistribute it and/or modify
it under the terms of the GNU Library General Public License as published by
the Free Software Foundation; either version 2 of the License, or (at your
option) any later version.

The GNU MP Library is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Library General Public
License for more details.

You should have received a copy of the GNU Library General Public License
along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
MA 02111-1307, USA.
*/

#include "gmp.h"
#include "gmp-impl.h"
#include "longlong.h"


/* This function is expected to be often used with b an odd prime, so the
   code for odd b is nice and short. */

int
#if __STDC__
mpz_kronecker_ui (mpz_srcptr a, unsigned long b)
#else
mpz_kronecker_ui (a, b)
     mpz_srcptr    a;
     unsigned long b;
#endif
{
  int  twos;

  if (b & 1)
    {
      if (b != 1)
        return mpn_jacobi_base (mpz_fdiv_ui (a, b), b, 0);
      else
        return 1;  /* (a/1)=1 for any a */
    }

  if (b == 0)
    return JACOBI_Z0 (a);

  /* (a/2)=0 if a even */
  if (mpz_even_p (a))
    return 0;

  /* (a/2)=(2/a) when a odd */
  count_trailing_zeros (twos, b);  
  b >>= twos;
  if (b == 1)
    return JACOBI_TWOS_U (twos, PTR(a)[0]);

  return mpn_jacobi_base (mpz_fdiv_ui (a, b), b,
                          JACOBI_TWOS_U_BIT1(twos, PTR(a)[0]));
}