xref: /src/external/lgpl3/gmp/dist/mpz/com.c

/* mpz_com(mpz_ptr dst, mpz_ptr src) -- Assign the bit-complemented value of
   SRC to DST.

Copyright 1991, 1993, 1994, 1996, 2001, 2003, 2012, 2015 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 either:

  * 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.

or

  * the GNU General Public License as published by the Free Software
    Foundation; either version 2 of the License, or (at your option) any
    later version.

or both in parallel, as here.

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 General Public License
for more details.

You should have received copies of the GNU General Public License and the
GNU Lesser General Public License along with the GNU MP Library.  If not,
see https://www.gnu.org/licenses/.  */

#include "gmp-impl.h"

void
mpz_com (mpz_ptr dst, mpz_srcptr src)
{
  mp_size_t size = SIZ (src);
  mp_srcptr src_ptr;
  mp_ptr dst_ptr;

  if (size >= 0)
    {
      /* As with infinite precision: one's complement, two's complement.
	 But this can be simplified using the identity -x = ~x + 1.
	 So we're going to compute (~~x) + 1 = x + 1!  */

      if (UNLIKELY (size == 0))
	{
	  /* special case, as mpn_add_1 wants size!=0 */
	  MPZ_NEWALLOC (dst, 1)[0] = 1;
	  SIZ (dst) = -1;
	}
      else
	{
	  mp_limb_t cy;

	  dst_ptr = MPZ_REALLOC (dst, size + 1);

	  src_ptr = PTR (src);

	  cy = mpn_add_1 (dst_ptr, src_ptr, size, (mp_limb_t) 1);
	  dst_ptr[size] = cy;
	  size += cy;

	  /* Store a negative size, to indicate ones-extension.  */
	  SIZ (dst) = -size;
      }
    }
  else
    {
      /* As with infinite precision: two's complement, then one's complement.
	 But that can be simplified using the identity -x = ~(x - 1).
	 So we're going to compute ~~(x - 1) = x - 1!  */
      size = -size;

      dst_ptr = MPZ_REALLOC (dst, size);

      src_ptr = PTR (src);

      mpn_sub_1 (dst_ptr, src_ptr, size, (mp_limb_t) 1);
      size -= dst_ptr[size - 1] == 0;

      /* Store a positive size, to indicate zero-extension.  */
      SIZ (dst) = size;
    }
}