freebsd-dev/contrib/libgmp/extract-double.c

/* __gmp_extract_double -- convert from double to array of mp_limb_t.

Copyright (C) 1996 Free Software Foundation, Inc.

This file is part of the GNU MP Library.

The GNU MP Library is free software; you can redistribute it and/or modify
it under the terms of the GNU Library General Public License as published by
the Free Software Foundation; either version 2 of the License, or (at your
option) any later version.

The GNU MP 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 Library General Public
License for more details.

You should have received a copy of the GNU Library General Public License
along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
MA 02111-1307, USA. */

#include "gmp.h"
#include "gmp-impl.h"

#ifdef XDEBUG
#undef _GMP_IEEE_FLOATS
#endif

#ifndef _GMP_IEEE_FLOATS
#define _GMP_IEEE_FLOATS 0
#endif

#define MP_BASE_AS_DOUBLE (2.0 * ((mp_limb_t) 1 << (BITS_PER_MP_LIMB - 1)))

/* Extract a non-negative double in d.  */

int
#if __STDC__
__gmp_extract_double (mp_ptr rp, double d)
#else
__gmp_extract_double (rp, d)
     mp_ptr rp;
     double d;
#endif
{
  long exp;
  unsigned sc;
  mp_limb_t manh, manl;

  /* BUGS

     1. Should handle Inf and NaN in IEEE specific code.
     2. Handle Inf and NaN also in default code, to avoid hangs.
     3. Generalize to handle all BITS_PER_MP_LIMB >= 32.
     4. This lits is incomplete and misspelled.
   */

  if (d == 0.0)
    {
      rp[0] = 0;
      rp[1] = 0;
#if BITS_PER_MP_LIMB == 32
      rp[2] = 0;
#endif
      return 0;
    }

#if _GMP_IEEE_FLOATS
  {
    union ieee_double_extract x;
    x.d = d;

    exp = x.s.exp;
    sc = (unsigned) (exp + 2) % BITS_PER_MP_LIMB;
#if BITS_PER_MP_LIMB == 64
    manl = (((mp_limb_t) 1 << 63)
	    | ((mp_limb_t) x.s.manh << 43) | ((mp_limb_t) x.s.manl << 11));
#else
    manh = ((mp_limb_t) 1 << 31) | (x.s.manh << 11) | (x.s.manl >> 21);
    manl = x.s.manl << 11;
#endif
  }
#else
  {
    /* Unknown (or known to be non-IEEE) double format.  */
    exp = 0;
    if (d >= 1.0)
      {
	if (d * 0.5 == d)
	  abort ();

	while (d >= 32768.0)
	  {
	    d *= (1.0 / 65536.0);
	    exp += 16;
	  }
	while (d >= 1.0)
	  {
	    d *= 0.5;
	    exp += 1;
	  }
      }
    else if (d < 0.5)
      {
	while (d < (1.0 / 65536.0))
	  {
	    d *=  65536.0;
	    exp -= 16;
	  }
	while (d < 0.5)
	  {
	    d *= 2.0;
	    exp -= 1;
	  }
      }

    sc = (unsigned) exp % BITS_PER_MP_LIMB;

    d *= MP_BASE_AS_DOUBLE;
#if BITS_PER_MP_LIMB == 64
    manl = d;
#else
    manh = d;
    manl = (d - manh) * MP_BASE_AS_DOUBLE;
#endif

    exp += 1022;
  }
#endif

  exp = (unsigned) (exp + 1) / BITS_PER_MP_LIMB - 1024 / BITS_PER_MP_LIMB + 1;

#if BITS_PER_MP_LIMB == 64
  if (sc != 0)
    {
      rp[1] = manl >> (BITS_PER_MP_LIMB - sc);
      rp[0] = manl << sc;
    }
  else
    {
      rp[1] = manl;
      rp[0] = 0;
    }
#else
  if (sc != 0)
    {
      rp[2] = manh >> (BITS_PER_MP_LIMB - sc);
      rp[1] = (manl >> (BITS_PER_MP_LIMB - sc)) | (manh << sc);
      rp[0] = manl << sc;
    }
  else
    {
      rp[2] = manh;
      rp[1] = manl;
      rp[0] = 0;
    }
#endif

  return exp;
}