xref: /dragonfly/contrib/mpfr/src/get_f.c (revision ab6d115f)

/* mpfr_get_f -- convert a MPFR number to a GNU MPF number

Copyright 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Free Software Foundation, Inc.
Contributed by the AriC and Caramel 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 3 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.LESSER.  If not, see
http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */

#include "mpfr-impl.h"

/* Since MPFR-3.0, return the usual inexact value.
   The erange flag is set if an error occurred in the conversion
   (y is NaN, +Inf, or -Inf that have no equivalent in mpf)
*/
int
mpfr_get_f (mpf_ptr x, mpfr_srcptr y, mpfr_rnd_t rnd_mode)
{
  int inex;
  mp_size_t sx, sy;
  mpfr_prec_t precx, precy;
  mp_limb_t *xp;
  int sh;

  if (MPFR_UNLIKELY(MPFR_IS_SINGULAR(y)))
    {
      if (MPFR_IS_ZERO(y))
        {
          mpf_set_ui (x, 0);
          return 0;
        }
      else if (MPFR_IS_NAN (y))
        {
          MPFR_SET_ERANGE ();
          return 0;
        }
      else /* y is plus infinity (resp. minus infinity), set x to the maximum
              value (resp. the minimum value) in precision PREC(x) */
        {
          int i;
          mp_limb_t *xp;

          MPFR_SET_ERANGE ();

          /* To this day, [mp_exp_t] and mp_size_t are #defined as the same
             type */
          EXP (x) = MP_SIZE_T_MAX;

          sx = PREC (x);
          SIZ (x) = sx;
          xp = PTR (x);
          for (i = 0; i < sx; i++)
            xp[i] = MP_LIMB_T_MAX;

          if (MPFR_IS_POS (y))
            return -1;
          else
            {
              mpf_neg (x, x);
              return +1;
            }
        }
    }

  sx = PREC(x); /* number of limbs of the mantissa of x */

  precy = MPFR_PREC(y);
  precx = (mpfr_prec_t) sx * GMP_NUMB_BITS;
  sy = MPFR_LIMB_SIZE (y);

  xp = PTR (x);

  /* since mpf numbers are represented in base 2^GMP_NUMB_BITS,
     we loose -EXP(y) % GMP_NUMB_BITS bits in the most significant limb */
  sh = MPFR_GET_EXP(y) % GMP_NUMB_BITS;
  sh = sh <= 0 ? - sh : GMP_NUMB_BITS - sh;
  MPFR_ASSERTD (sh >= 0);
  if (precy + sh <= precx) /* we can copy directly */
    {
      mp_size_t ds;

      MPFR_ASSERTN (sx >= sy);
      ds = sx - sy;

      if (sh != 0)
        {
          mp_limb_t out;
          out = mpn_rshift (xp + ds, MPFR_MANT(y), sy, sh);
          MPFR_ASSERTN (ds > 0 || out == 0);
          if (ds > 0)
            xp[--ds] = out;
        }
      else
        MPN_COPY (xp + ds, MPFR_MANT (y), sy);
      if (ds > 0)
        MPN_ZERO (xp, ds);
      EXP(x) = (MPFR_GET_EXP(y) + sh) / GMP_NUMB_BITS;
      inex = 0;
    }
  else /* we have to round to precx - sh bits */
    {
      mpfr_t z;
      mp_size_t sz;

      /* Recall that precx = (mpfr_prec_t) sx * GMP_NUMB_BITS, thus removing
         sh bits (sh < GMP_NUMB_BITSS) won't reduce the number of limbs. */
      mpfr_init2 (z, precx - sh);
      sz = MPFR_LIMB_SIZE (z);
      MPFR_ASSERTN (sx == sz);

      inex = mpfr_set (z, y, rnd_mode);
      /* warning, sh may change due to rounding, but then z is a power of two,
         thus we can safely ignore its last bit which is 0 */
      sh = MPFR_GET_EXP(z) % GMP_NUMB_BITS;
      sh = sh <= 0 ? - sh : GMP_NUMB_BITS - sh;
      MPFR_ASSERTD (sh >= 0);
      if (sh != 0)
        {
          mp_limb_t out;
          out = mpn_rshift (xp, MPFR_MANT(z), sz, sh);
          /* If sh hasn't changed, it is the number of the non-significant
             bits in the lowest limb of z. Therefore out == 0. */
          MPFR_ASSERTD (out == 0);  (void) out; /* avoid a warning */
        }
      else
        MPN_COPY (xp, MPFR_MANT(z), sz);
      EXP(x) = (MPFR_GET_EXP(z) + sh) / GMP_NUMB_BITS;
      mpfr_clear (z);
    }

  /* set size and sign */
  SIZ(x) = (MPFR_FROM_SIGN_TO_INT(MPFR_SIGN(y)) < 0) ? -sx : sx;

  return inex;
}