inv.c revision 1.1.1.1 
1/* mpq_inv(dest,src) -- invert a rational number, i.e. set DEST to SRC
2   with the numerator and denominator swapped.
3
4Copyright 1991, 1994, 1995, 2000, 2001 Free Software Foundation, Inc.
5
6This file is part of the GNU MP Library.
7
8The GNU MP Library is free software; you can redistribute it and/or modify
9it under the terms of the GNU Lesser General Public License as published by
10the Free Software Foundation; either version 3 of the License, or (at your
11option) any later version.
12
13The GNU MP Library is distributed in the hope that it will be useful, but
14WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
15or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
16License for more details.
17
18You should have received a copy of the GNU Lesser General Public License
19along with the GNU MP Library.  If not, see http://www.gnu.org/licenses/.  */
20
21#include "gmp.h"
22#include "gmp-impl.h"
23
24void
25mpq_inv (MP_RAT *dest, const MP_RAT *src)
26{
27  mp_size_t num_size = src->_mp_num._mp_size;
28  mp_size_t den_size = src->_mp_den._mp_size;
29
30  if (num_size == 0)
31    DIVIDE_BY_ZERO;
32
33  if (num_size < 0)
34    {
35      num_size = -num_size;
36      den_size = -den_size;
37    }
38  dest->_mp_den._mp_size = num_size;
39  dest->_mp_num._mp_size = den_size;
40
41  /* If dest == src we may just swap the numerator and denominator, but
42     we have to ensure the new denominator is positive.  */
43
44  if (dest == src)
45    {
46      mp_size_t alloc = dest->_mp_num._mp_alloc;
47      mp_ptr limb_ptr = dest->_mp_num._mp_d;
48
49      dest->_mp_num._mp_alloc = dest->_mp_den._mp_alloc;
50      dest->_mp_num._mp_d = dest->_mp_den._mp_d;
51
52      dest->_mp_den._mp_alloc = alloc;
53      dest->_mp_den._mp_d = limb_ptr;
54    }
55  else
56    {
57      den_size = ABS (den_size);
58      if (dest->_mp_num._mp_alloc < den_size)
59	_mpz_realloc (&(dest->_mp_num), den_size);
60
61      if (dest->_mp_den._mp_alloc < num_size)
62	_mpz_realloc (&(dest->_mp_den), num_size);
63
64      MPN_COPY (dest->_mp_num._mp_d, src->_mp_den._mp_d, den_size);
65      MPN_COPY (dest->_mp_den._mp_d, src->_mp_num._mp_d, num_size);
66    }
67}
68