extract-dbl.c

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

Copyright 1996, 1999, 2000, 2001, 2002, 2006 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 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 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 Lesser General Public
License for more details.

You should have received a copy of the GNU Lesser General Public License
along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
MA 02110-1301, USA. */

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

#define BITS_IN_MANTISSA 53

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

int
__gmp_extract_double (mp_ptr rp, double d)
{
  long exp;
  unsigned sc;
#ifdef _LONG_LONG_LIMB
#define BITS_PER_PART 64	/* somewhat bogus */
  unsigned long long int manl;
#else
#define BITS_PER_PART GMP_LIMB_BITS
  unsigned long int manh, manl;
#endif

  /* 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 GMP_LIMB_BITS >= 32.
     4. This lits is incomplete and misspelled.
   */

  ASSERT (d >= 0.0);

  if (d == 0.0)
    {
      MPN_ZERO (rp, LIMBS_PER_DOUBLE);
      return 0;
    }

#if 1
  {
    union ieee_double_extract x;
    x.d = d;
    exp = x.s.exp;
#if BITS_PER_PART == 64		/* generalize this to BITS_PER_PART > BITS_IN_MANTISSA */
    manl = (((mp_limb_t) 1 << 63)
	    | ((mp_limb_t) x.s.manh << 43) | ((mp_limb_t) x.s.manl << 11));
    if (exp == 0)
      {
	/* Denormalized number.  Don't try to be clever about this,
	   since it is not an important case to make fast.  */
	exp = 1;
	do
	  {
	    manl = manl << 1;
	    exp--;
	  }
	while ((manl & GMP_LIMB_HIGHBIT) == 0);
      }
#endif
#if BITS_PER_PART == 32
    manh = ((mp_limb_t) 1 << 31) | (x.s.manh << 11) | (x.s.manl >> 21);
    manl = x.s.manl << 11;
    if (exp == 0)
      {
	/* Denormalized number.  Don't try to be clever about this,
	   since it is not an important case to make fast.  */
	exp = 1;
	do
	  {
	    manh = (manh << 1) | (manl >> 31);
	    manl = manl << 1;
	    exp--;
	  }
	while ((manh & GMP_LIMB_HIGHBIT) == 0);
      }
#endif
#if BITS_PER_PART != 32 && BITS_PER_PART != 64
  You need to generalize the code above to handle this.
#endif
    exp -= 1022;		/* Remove IEEE bias.  */
  }
#else
  {
    /* Unknown (or known to be non-IEEE) double format.  */
    exp = 0;
    if (d >= 1.0)
      {
	ASSERT_ALWAYS (d * 0.5 != d);

	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;
	  }
      }

    d *= (4.0 * ((unsigned long int) 1 << (BITS_PER_PART - 2)));
#if BITS_PER_PART == 64
    manl = d;
#else
    manh = d;
    manl = (d - manh) * (4.0 * ((unsigned long int) 1 << (BITS_PER_PART - 2)));
#endif
  }
#endif /* IEEE */

  /* Up until here, we have ignored the actual limb size.  Remains
     to split manh,,manl into an array of LIMBS_PER_DOUBLE limbs.
  */

  sc = (unsigned) (exp + 64 * GMP_NUMB_BITS) % GMP_NUMB_BITS;

  /* We add something here to get rounding right.  */
  exp = (exp + 64 * GMP_NUMB_BITS) / GMP_NUMB_BITS - 64 * GMP_NUMB_BITS / GMP_NUMB_BITS + 1;

#if LIMBS_PER_DOUBLE == 2
#if GMP_NAIL_BITS == 0
  if (sc != 0)
    {
      rp[1] = manl >> (GMP_LIMB_BITS - sc);
      rp[0] = manl << sc;
    }
  else
    {
      rp[1] = manl;
      rp[0] = 0;
      exp--;
    }
#else
  if (sc > GMP_NAIL_BITS)
    {
      rp[1] = manl >> (GMP_LIMB_BITS - sc);
      rp[0] = (manl << (sc - GMP_NAIL_BITS)) & GMP_NUMB_MASK;
    }
  else
    {
      if (sc == 0)
	{
	  rp[1] = manl >> GMP_NAIL_BITS;
	  rp[0] = (manl << GMP_NUMB_BITS - GMP_NAIL_BITS) & GMP_NUMB_MASK;
	  exp--;
	}
      else
	{
	  rp[1] = manl >> (GMP_LIMB_BITS - sc);
	  rp[0] = (manl >> (GMP_NAIL_BITS - sc)) & GMP_NUMB_MASK;
	}
    }
#endif
#endif

#if LIMBS_PER_DOUBLE == 3
#if GMP_NAIL_BITS == 0
  if (sc != 0)
    {
      rp[2] = manh >> (GMP_LIMB_BITS - sc);
      rp[1] = (manh << sc) | (manl >> (GMP_LIMB_BITS - sc));
      rp[0] = manl << sc;
    }
  else
    {
      rp[2] = manh;
      rp[1] = manl;
      rp[0] = 0;
      exp--;
    }
#else
  if (sc > GMP_NAIL_BITS)
    {
      rp[2] = (manh >> (GMP_LIMB_BITS - sc));
      rp[1] = ((manh << (sc - GMP_NAIL_BITS)) |
	       (manl >> (GMP_LIMB_BITS - sc + GMP_NAIL_BITS))) & GMP_NUMB_MASK;
      if (sc >= 2 * GMP_NAIL_BITS)
	rp[0] = (manl << sc - 2 * GMP_NAIL_BITS) & GMP_NUMB_MASK;
      else
	rp[0] = manl >> (2 * GMP_NAIL_BITS - sc) & GMP_NUMB_MASK;
    }
  else
    {
      if (sc == 0)
	{
	  rp[2] = manh >> GMP_NAIL_BITS;
	  rp[1] = ((manh << GMP_NUMB_BITS - GMP_NAIL_BITS) | (manl >> 2 * GMP_NAIL_BITS)) & GMP_NUMB_MASK;
	  rp[0] = 0;
	  exp--;
	}
      else
	{
	  rp[2] = (manh >> (GMP_LIMB_BITS - sc));
	  rp[1] = (manh >> (GMP_NAIL_BITS - sc)) & GMP_NUMB_MASK;
	  rp[0] = ((manh << (GMP_NUMB_BITS - GMP_NAIL_BITS + sc))
		   | (manl >> (GMP_LIMB_BITS - (GMP_NUMB_BITS - GMP_NAIL_BITS + sc)))) & GMP_NUMB_MASK;
	}
    }
#endif
#endif

#if LIMBS_PER_DOUBLE > 3
  if (sc == 0)
    {
      int i;

      for (i = LIMBS_PER_DOUBLE - 1; i >= 0; i--)
	{
	  rp[i] = manh >> (BITS_PER_ULONG - GMP_NUMB_BITS);
	  manh = ((manh << GMP_NUMB_BITS)
		  | (manl >> (BITS_PER_ULONG - GMP_NUMB_BITS)));
	  manl = manl << GMP_NUMB_BITS;
	}
      exp--;
    }
  else
    {
      int i;

      rp[LIMBS_PER_DOUBLE - 1] = (manh >> (GMP_LIMB_BITS - sc));
      manh = (manh << sc) | (manl >> (GMP_LIMB_BITS - sc));
      manl = (manl << sc);
      for (i = LIMBS_PER_DOUBLE - 2; i >= 0; i--)
	{
	  rp[i] = manh >> (BITS_PER_ULONG - GMP_NUMB_BITS);
	  manh = ((manh << GMP_NUMB_BITS)
		  | (manl >> (BITS_PER_ULONG - GMP_NUMB_BITS)));
	  manl = manl << GMP_NUMB_BITS;
	}
  }
#endif

  return exp;
}