/* Copyright (C) 1993-2018 Free Software Foundation, Inc.

   This file is part of the GNU C Library.

   The GNU C 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 C 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 C Library; if not, see

   <http://www.gnu.org/licenses/>.  */

#include "gmp.h"

#include "gmp-impl.h"

#include "longlong.h"

#include <ieee754.h>

#include <float.h>

#include <stdlib.h>

/* Convert a `double' in IEEE754 standard double-precision format to a

   multi-precision integer representing the significand scaled up by its

   number of bits (52 for double) and an integral power of two (MPN frexp). */

mp_size_t

__mpn_extract_double (mp_ptr res_ptr, mp_size_t size,

		      int *expt, int *is_neg,

		      double value)

{

  union ieee754_double u;

  u.d = value;

  *is_neg = u.ieee.negative;

  *expt = (int) u.ieee.exponent - IEEE754_DOUBLE_BIAS;

#if BITS_PER_MP_LIMB == 32

  res_ptr[0] = u.ieee.mantissa1; /* Low-order 32 bits of fraction.  */

  res_ptr[1] = u.ieee.mantissa0; /* High-order 20 bits.  */

  # define N 2

#elif BITS_PER_MP_LIMB == 64

  /* Hopefully the compiler will combine the two bitfield extracts

     and this composition into just the original quadword extract.  */

  res_ptr[0] = ((mp_limb_t) u.ieee.mantissa0 << 32) | u.ieee.mantissa1;

  # define N 1

#else

  # error "mp_limb size " BITS_PER_MP_LIMB "not accounted for"

#endif

/* The format does not fill the last limb.  There are some zeros.  */

#define NUM_LEADING_ZEROS (BITS_PER_MP_LIMB \

			   - (DBL_MANT_DIG - ((N - 1) * BITS_PER_MP_LIMB)))

  if (u.ieee.exponent == 0)

    {

      /* A biased exponent of zero is a special case.

	 Either it is a zero or it is a denormal number.  */

      if (res_ptr[0] == 0 && res_ptr[N - 1] == 0) /* Assumes N<=2.  */

	/* It's zero.  */

	*expt = 0;

      else

	{

          /* It is a denormal number, meaning it has no implicit leading

	     one bit, and its exponent is in fact the format minimum.  */

	  int cnt;

	  if (res_ptr[N - 1] != 0)

	    {

	      count_leading_zeros (cnt, res_ptr[N - 1]);

	      cnt -= NUM_LEADING_ZEROS;

#if N == 2

	      res_ptr[N - 1] = res_ptr[1] << cnt

			       | (N - 1)

			       * (res_ptr[0] >> (BITS_PER_MP_LIMB - cnt));

	      res_ptr[0] <<= cnt;

#else

	      res_ptr[N - 1] <<= cnt;

#endif

	      *expt = DBL_MIN_EXP - 1 - cnt;

	    }

	  else

	    {

	      count_leading_zeros (cnt, res_ptr[0]);

	      if (cnt >= NUM_LEADING_ZEROS)

		{

		  res_ptr[N - 1] = res_ptr[0] << (cnt - NUM_LEADING_ZEROS);

		  res_ptr[0] = 0;

		}

	      else

		{

		  res_ptr[N - 1] = res_ptr[0] >> (NUM_LEADING_ZEROS - cnt);

		  res_ptr[0] <<= BITS_PER_MP_LIMB - (NUM_LEADING_ZEROS - cnt);

		}

	      *expt = DBL_MIN_EXP - 1

		      - (BITS_PER_MP_LIMB - NUM_LEADING_ZEROS) - cnt;

	    }

	}

    }

  else

    /* Add the implicit leading one bit for a normalized number.  */

    res_ptr[N - 1] |= (mp_limb_t) 1 << (DBL_MANT_DIG - 1

					- ((N - 1) * BITS_PER_MP_LIMB));

  return N;

}