xref: /dflybsd-src/contrib/mpfr/src/get_z_exp.c (revision 2786097444a0124b5d33763854de247e230c6629)

/* mpfr_get_z_2exp -- get a multiple-precision integer and an exponent
                      from a floating-point number

Copyright 2000, 2001, 2002, 2003, 2004, 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"

/* puts the significand of f into z, and returns 'exp' such that f = z * 2^exp
 *
 * 0 doesn't have an exponent, therefore the returned exponent in this case
 * isn't really important. We choose to return __gmpfr_emin because
 *   1) it is in the exponent range [__gmpfr_emin,__gmpfr_emax],
 *   2) the smaller a number is (in absolute value), the smaller its
 *      exponent is. In other words, the f -> exp function is monotonous
 *      on nonnegative numbers. --> This is WRONG since the returned
 *      exponent is not necessarily in the exponent range!
 * Note that this is different from the C function frexp().
 *
 * For NaN and infinities, we choose to set z = 0 (neutral value).
 * The exponent doesn't really matter, so let's keep __gmpfr_emin
 * for consistency. The erange flag is set.
 */

mpfr_exp_t
mpfr_get_z_2exp (mpz_ptr z, mpfr_srcptr f)
{
  mp_size_t fn;
  int sh;

  if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (f)))
    {
      if (MPFR_UNLIKELY (MPFR_NOTZERO (f)))
        MPFR_SET_ERANGE ();
      mpz_set_ui (z, 0);
      return __gmpfr_emin;
    }

  fn = MPFR_LIMB_SIZE(f);

  /* check whether allocated space for z is enough */
  if (MPFR_UNLIKELY (ALLOC (z) < fn))
    MPZ_REALLOC (z, fn);

  MPFR_UNSIGNED_MINUS_MODULO (sh, MPFR_PREC (f));
  if (MPFR_LIKELY (sh))
    mpn_rshift (PTR (z), MPFR_MANT (f), fn, sh);
  else
    MPN_COPY (PTR (z), MPFR_MANT (f), fn);

  SIZ(z) = MPFR_IS_NEG (f) ? -fn : fn;

  if (MPFR_UNLIKELY ((mpfr_uexp_t) MPFR_GET_EXP (f) - MPFR_EXP_MIN
                     < (mpfr_uexp_t) MPFR_PREC (f)))
    {
      /* The exponent isn't representable in an mpfr_exp_t. */
      MPFR_SET_ERANGE ();
      return MPFR_EXP_MIN;
    }

  return MPFR_GET_EXP (f) - MPFR_PREC (f);
}