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  
       7  Copyright 2008, 2010 Free Software Foundation, Inc.
       8  
       9  This file is part of the GNU MP Library.
      10  
      11  The GNU MP Library is free software; you can redistribute it and/or modify
      12  it 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  
      18  or
      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  
      24  or both in parallel, as here.
      25  
      26  The GNU MP Library is distributed in the hope that it will be useful, but
      27  WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
      28  or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
      29  for more details.
      30  
      31  You should have received copies of the GNU General Public License and the
      32  GNU Lesser General Public License along with the GNU MP Library.  If not,
      33  see 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. */
      40  mp_size_t
      41  mpn_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  }