/* mpfr_nextabove, mpfr_nextbelow, mpfr_nexttoward -- next representable
floating-point number

Copyright 1999, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
Contributed by the Arenaire and Cacao projects, INRIA.

This file is part of the GNU MPFR Library.

The GNU MPFR 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 MPFR 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 MPFR Library; see the file COPYING.LIB.  If not, write to
the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston,
MA 02110-1301, USA. */

#include "mpfr-impl.h"

void
mpfr_nexttozero (mpfr_ptr x)
{
  if (MPFR_UNLIKELY(MPFR_IS_INF(x)))
    {
      MPFR_CLEAR_FLAGS(x);
      mpfr_setmax (x, __gmpfr_emax);
      return;
    }
  else if (MPFR_UNLIKELY( MPFR_IS_ZERO(x) ))
    {
      MPFR_CHANGE_SIGN(x);
      mpfr_setmin (x, __gmpfr_emin);
    }
  else
    {
      mp_size_t xn;
      int sh;
      mp_limb_t *xp;

      xn = MPFR_LIMB_SIZE (x);
      MPFR_UNSIGNED_MINUS_MODULO (sh, MPFR_PREC(x));
      xp = MPFR_MANT(x);
      mpn_sub_1 (xp, xp, xn, MPFR_LIMB_ONE << sh);
      if (MPFR_UNLIKELY( MPFR_LIMB_MSB(xp[xn-1]) == 0) )
        { /* was an exact power of two: not normalized any more */
          mp_exp_t exp = MPFR_EXP (x);
          if (MPFR_UNLIKELY(exp == __gmpfr_emin))
            MPFR_SET_ZERO(x);
          else
            {
              mp_size_t i;
              MPFR_SET_EXP (x, exp - 1);
              xp[0] = MP_LIMB_T_MAX << sh;
              for (i = 1; i < xn; i++)
                xp[i] = MP_LIMB_T_MAX;
            }
        }
    }
}

void
mpfr_nexttoinf (mpfr_ptr x)
{
  if (MPFR_UNLIKELY(MPFR_IS_INF(x)))
    return;
  else if (MPFR_UNLIKELY(MPFR_IS_ZERO(x)))
    mpfr_setmin (x, __gmpfr_emin);
  else
    {
      mp_size_t xn;
      int sh;
      mp_limb_t *xp;

      xn = MPFR_LIMB_SIZE (x);
      MPFR_UNSIGNED_MINUS_MODULO (sh, MPFR_PREC(x));
      xp = MPFR_MANT(x);
      if (MPFR_UNLIKELY( mpn_add_1 (xp, xp, xn, MPFR_LIMB_ONE << sh)) )
        /* got 1.0000... */
        {
          mp_exp_t exp = MPFR_EXP (x);
          if (MPFR_UNLIKELY(exp == __gmpfr_emax))
            MPFR_SET_INF(x);
          else
            {
              MPFR_SET_EXP (x, exp + 1);
              xp[xn-1] = MPFR_LIMB_HIGHBIT;
            }
        }
    }
}

void
mpfr_nextabove (mpfr_ptr x)
{
  if (MPFR_UNLIKELY(MPFR_IS_NAN(x)))
    {
      __gmpfr_flags |= MPFR_FLAGS_NAN;
      return;
    }
  if (MPFR_IS_NEG(x))
    mpfr_nexttozero (x);
  else
    mpfr_nexttoinf (x);
}

void
mpfr_nextbelow (mpfr_ptr x)
{
  if (MPFR_UNLIKELY(MPFR_IS_NAN(x)))
    {
      __gmpfr_flags |= MPFR_FLAGS_NAN;
      return;
    }

  if (MPFR_IS_NEG(x))
    mpfr_nexttoinf (x);
  else
    mpfr_nexttozero (x);
}

void
mpfr_nexttoward (mpfr_ptr x, mpfr_srcptr y)
{
  int s;

  if (MPFR_UNLIKELY(MPFR_IS_NAN(x)))
    {
      __gmpfr_flags |= MPFR_FLAGS_NAN;
      return;
    }
  else if (MPFR_UNLIKELY(MPFR_IS_NAN(x) || MPFR_IS_NAN(y)))
    {
      MPFR_SET_NAN(x);
      __gmpfr_flags |= MPFR_FLAGS_NAN;
      return;
    }

  s = mpfr_cmp (x, y);
  if (s == 0)
    return;
  else if (s < 0)
    mpfr_nextabove (x);
  else
    mpfr_nextbelow (x);
}
