1/* matrix22_mul1_inverse_vector.c
2
3   THE FUNCTIONS IN THIS FILE ARE INTERNAL WITH MUTABLE INTERFACES.  IT IS ONLY
4   SAFE TO REACH THEM THROUGH DOCUMENTED INTERFACES.  IN FACT, IT IS ALMOST
5   GUARANTEED THAT THEY'LL CHANGE OR DISAPPEAR IN A FUTURE GNU MP RELEASE.
6
7Copyright 2008, 2010 Free Software Foundation, Inc.
8
9This file is part of the GNU MP Library.
10
11The GNU MP Library is free software; you can redistribute it and/or modify
12it under the terms of either:
13
14  * the GNU Lesser General Public License as published by the Free
15    Software Foundation; either version 3 of the License, or (at your
16    option) any later version.
17
18or
19
20  * the GNU General Public License as published by the Free Software
21    Foundation; either version 2 of the License, or (at your option) any
22    later version.
23
24or both in parallel, as here.
25
26The GNU MP Library is distributed in the hope that it will be useful, but
27WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
28or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
29for more details.
30
31You should have received copies of the GNU General Public License and the
32GNU Lesser General Public License along with the GNU MP Library.  If not,
33see https://www.gnu.org/licenses/.  */
34
35#include "gmp-impl.h"
36#include "longlong.h"
37
38/* Sets (r;b) = M^{-1}(a;b), with M^{-1} = (u11, -u01; -u10, u00) from
39   the left. Uses three buffers, to avoid a copy. */
40mp_size_t
41mpn_matrix22_mul1_inverse_vector (const struct hgcd_matrix1 *M,
42				  mp_ptr rp, mp_srcptr ap, mp_ptr bp, mp_size_t n)
43{
44  mp_limb_t h0, h1;
45
46  /* Compute (r;b) <-- (u11 a - u01 b; -u10 a + u00 b) as
47
48     r  = u11 * a
49     r -= u01 * b
50     b *= u00
51     b -= u10 * a
52  */
53
54  h0 =    mpn_mul_1 (rp, ap, n, M->u[1][1]);
55  h1 = mpn_submul_1 (rp, bp, n, M->u[0][1]);
56  ASSERT (h0 == h1);
57
58  h0 =    mpn_mul_1 (bp, bp, n, M->u[0][0]);
59  h1 = mpn_submul_1 (bp, ap, n, M->u[1][0]);
60  ASSERT (h0 == h1);
61
62  n -= (rp[n-1] | bp[n-1]) == 0;
63  return n;
64}
65