mpir/mpz/cdiv_qr_ui.c

/* mpz_cdiv_qr_ui -- Division rounding the quotient towards +infinity.  The
   remainder gets the opposite sign as the denominator.  In order to make it
   always fit into the return type, the negative of the true remainder is
   returned.

Copyright 1994, 1995, 1996, 1999, 2001, 2002, 2004 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 Lesser General Public License as published by
the Free Software Foundation; either version 2.1 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 Lesser General Public
License for more details.

You should have received a copy of the GNU Lesser General Public License
along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
MA 02110-1301, USA. */

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

unsigned long int
mpz_cdiv_qr_ui (mpz_ptr quot, mpz_ptr rem, mpz_srcptr dividend, unsigned long int divisor)
{
  mp_size_t ns, nn, qn;
  mp_ptr np, qp;
  mp_limb_t rl;

  if (divisor == 0)
    DIVIDE_BY_ZERO;

  ns = SIZ(dividend);
  if (ns == 0)
    {
      SIZ(quot) = 0;
      SIZ(rem) = 0;
      return 0;
    }

  nn = ABS(ns);
  MPZ_REALLOC (quot, nn);
  qp = PTR(quot);
  np = PTR(dividend);

#if BITS_PER_ULONG > GMP_NUMB_BITS  /* avoid warnings about shift amount */
  if (divisor > GMP_NUMB_MAX)
    {
      mp_limb_t dp[2];
      mp_ptr rp;
      mp_size_t rn;

      MPZ_REALLOC (rem, 2);
      rp = PTR(rem);

      if (nn == 1)		/* tdiv_qr requirements; tested above for 0 */
	{
	  qp[0] = 0;
	  qn = 1;		/* a white lie, fixed below */
	  rl = np[0];
	  rp[0] = rl;
	}
      else
	{
	  dp[0] = divisor & GMP_NUMB_MASK;
	  dp[1] = divisor >> GMP_NUMB_BITS;
	  mpn_tdiv_qr (qp, rp, (mp_size_t) 0, np, nn, dp, (mp_size_t) 2);
	  rl = rp[0] + (rp[1] << GMP_NUMB_BITS);
	  qn = nn - 2 + 1; 
	}

      if (rl != 0 && ns >= 0)
	{
	  mpn_incr_u (qp, (mp_limb_t) 1);
	  rl = divisor - rl;
	  rp[0] = rl & GMP_NUMB_MASK;
	  rp[1] = rl >> GMP_NUMB_BITS;
	}

      qn -= qp[qn - 1] == 0; qn -= qn != 0 && qp[qn - 1] == 0;
      rn = 1 + (rl > GMP_NUMB_MAX);  rn -= (rp[rn - 1] == 0);
      SIZ(rem) = -rn;
    }
  else
#endif
    {
      rl = mpn_divrem_1 (qp, 0, np, nn, (mp_limb_t) divisor);
      if (rl == 0)
	SIZ(rem) = 0;
      else
	{
	  if (ns >= 0)
	    {
	      mpn_incr_u (qp, (mp_limb_t) 1);
	      rl = divisor - rl;
	    }

	  PTR(rem)[0] = rl;
	  SIZ(rem) = -(rl != 0);
	}
      qn = nn - (qp[nn - 1] == 0);
    }

  SIZ(quot) = ns >= 0 ? qn : -qn;
  return rl;
}