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

/* mpfr_get_sj -- convert a MPFR number to a huge machine signed integer

Copyright 2004, 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. */

#ifdef HAVE_CONFIG_H
# include "config.h"            /* for a build within gmp */
#endif

#include "mpfr-intmax.h"
#include "mpfr-impl.h"

#ifdef _MPFR_H_HAVE_INTMAX_T

intmax_t
mpfr_get_sj (mpfr_srcptr f, mpfr_rnd_t rnd)
{
  intmax_t r;
  mpfr_prec_t prec;
  mpfr_t x;

  if (MPFR_UNLIKELY (!mpfr_fits_intmax_p (f, rnd)))
    {
      MPFR_SET_ERANGE ();
      return MPFR_IS_NAN (f) ? 0 :
        MPFR_IS_NEG (f) ? MPFR_INTMAX_MIN : MPFR_INTMAX_MAX;
    }

  if (MPFR_IS_ZERO (f))
     return (intmax_t) 0;

  /* determine the precision of intmax_t */
  for (r = MPFR_INTMAX_MIN, prec = 0; r != 0; r /= 2, prec++)
    { }
  /* Note: though INTMAX_MAX would have been sufficient for the conversion,
     we chose INTMAX_MIN so that INTMAX_MIN - 1 is always representable in
     precision prec; this is useful to detect overflows in MPFR_RNDZ (will
     be needed later). */

  /* Now, r = 0. */

  mpfr_init2 (x, prec);
  mpfr_rint (x, f, rnd);
  MPFR_ASSERTN (MPFR_IS_FP (x));

  if (MPFR_NOTZERO (x))
    {
      mp_limb_t *xp;
      int sh, n;        /* An int should be sufficient in this context. */

      xp = MPFR_MANT (x);
      sh = MPFR_GET_EXP (x);
      MPFR_ASSERTN ((mpfr_prec_t) sh <= prec);
      if (MPFR_INTMAX_MIN + MPFR_INTMAX_MAX != 0
          && MPFR_UNLIKELY ((mpfr_prec_t) sh == prec))
        {
          /* 2's complement and x <= INTMAX_MIN: in the case mp_limb_t
             has the same size as intmax_t, we cannot use the code in
             the for loop since the operations would be performed in
             unsigned arithmetic. */
          MPFR_ASSERTN (MPFR_IS_NEG (x) && (mpfr_powerof2_raw (x)));
          r = MPFR_INTMAX_MIN;
        }
      else if (MPFR_IS_POS (x))
        {
          /* Note: testing the condition sh >= 0 is necessary to avoid
             an undefined behavior on xp[n] >> S when S >= GMP_NUMB_BITS
             (even though xp[n] == 0 in such a case). This can happen if
             sizeof(mp_limb_t) < sizeof(intmax_t) and |x| is small enough
             because of the trailing bits due to its normalization. */
          for (n = MPFR_LIMB_SIZE (x) - 1; n >= 0 && sh >= 0; n--)
            {
              sh -= GMP_NUMB_BITS;
              /* Note the concerning the casts below:
                 When sh >= 0, the cast must be performed before the shift
                 for the case sizeof(intmax_t) > sizeof(mp_limb_t).
                 When sh < 0, the cast must be performed after the shift
                 for the case sizeof(intmax_t) == sizeof(mp_limb_t), as
                 mp_limb_t is unsigned, therefore not representable as an
                 intmax_t when the MSB is 1 (this is the case here). */
              MPFR_ASSERTD (sh < GMP_NUMB_BITS && -sh < GMP_NUMB_BITS);
              r += (sh >= 0
                    ? (intmax_t) xp[n] << sh
                    : (intmax_t) (xp[n] >> (-sh)));
            }
        }
      else
        {
          /* See the comments for the case x positive. */
          for (n = MPFR_LIMB_SIZE (x) - 1; n >= 0 && sh >= 0; n--)
            {
              sh -= GMP_NUMB_BITS;
              MPFR_ASSERTD (sh < GMP_NUMB_BITS && -sh < GMP_NUMB_BITS);
              r -= (sh >= 0
                    ? (intmax_t) xp[n] << sh
                    : (intmax_t) (xp[n] >> (-sh)));
            }
        }
    }

  mpfr_clear (x);

  return r;
}

#endif