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

/* mpfr_set_f -- set a MPFR number from a GNU MPF number

Copyright 1999, 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. */

#define MPFR_NEED_LONGLONG_H
#include "mpfr-impl.h"

int
mpfr_set_f (mpfr_ptr y, mpf_srcptr x, mpfr_rnd_t rnd_mode)
{
  mp_limb_t *my, *mx, *tmp;
  unsigned long cnt, sx, sy;
  int inexact, carry = 0;
  MPFR_TMP_DECL(marker);

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

  if (sx == 0) /* x is zero */
    {
      MPFR_SET_ZERO(y);
      MPFR_SET_POS(y);
      return 0; /* 0 is exact */
    }

  if (SIZ(x) * MPFR_FROM_SIGN_TO_INT(MPFR_SIGN(y)) < 0)
    MPFR_CHANGE_SIGN (y);

  sy = MPFR_LIMB_SIZE (y);
  my = MPFR_MANT(y);
  mx = PTR(x);

  count_leading_zeros(cnt, mx[sx - 1]);

  if (sy <= sx) /* we may have to round even when sy = sx */
    {
      unsigned long xprec = sx * GMP_NUMB_BITS;

      MPFR_TMP_MARK(marker);
      tmp = MPFR_TMP_LIMBS_ALLOC (sx);
      if (cnt)
        mpn_lshift (tmp, mx, sx, cnt);
      else
        /* FIXME: we may avoid the copy here, and directly call mpfr_round_raw
           on mx instead of tmp */
        MPN_COPY (tmp, mx, sx);
      carry = mpfr_round_raw (my, tmp, xprec, (SIZ(x) < 0), MPFR_PREC(y),
                              rnd_mode, &inexact);
      if (MPFR_UNLIKELY(carry)) /* result is a power of two */
        my[sy - 1] = MPFR_LIMB_HIGHBIT;
      MPFR_TMP_FREE(marker);
    }
  else
    {
      if (cnt)
        mpn_lshift (my + sy - sx, mx, sx, cnt);
      else
        MPN_COPY (my + sy - sx, mx, sx);
      MPN_ZERO(my, sy - sx);
      /* no rounding necessary, since y has a larger mantissa */
      inexact = 0;
    }

  /* warning: EXP(x) * GMP_NUMB_BITS may exceed the maximal exponent */
  if (EXP(x) > 1 + (__gmpfr_emax - 1) / GMP_NUMB_BITS)
    {
      /* EXP(x) >= 2 + floor((__gmpfr_emax-1)/GMP_NUMB_BITS)
         EXP(x) >= 2 + (__gmpfr_emax - GMP_NUMB_BITS) / GMP_NUMB_BITS
                >= 1 + __gmpfr_emax / GMP_NUMB_BITS
         EXP(x) * GMP_NUMB_BITS >= __gmpfr_emax + GMP_NUMB_BITS
         Since 0 <= cnt <= GMP_NUMB_BITS-1, and 0 <= carry <= 1,
         we have then EXP(x) * GMP_NUMB_BITS - cnt + carry > __gmpfr_emax */
      return mpfr_overflow (y, rnd_mode, MPFR_SIGN (y));
    }
  else
    {
      /* Do not use MPFR_SET_EXP as the exponent may be out of range. */
      MPFR_EXP (y) = EXP (x) * GMP_NUMB_BITS - (mpfr_exp_t) cnt + carry;
    }

  return mpfr_check_range (y, inexact, rnd_mode);
}