1  /* mpn_redc_n.  Set rp[] <- up[]/R^n mod mp[].  Clobber up[].
       2     mp[] is n limbs; up[] is 2n limbs, the inverse ip[] is n limbs.
       3  
       4     THIS IS AN INTERNAL FUNCTION WITH A MUTABLE INTERFACE.  IT IS ONLY
       5     SAFE TO REACH THIS FUNCTION THROUGH DOCUMENTED INTERFACES.
       6  
       7  Copyright 2009, 2012 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  
      37  /*
      38    TODO
      39  
      40    * We assume mpn_mulmod_bnm1 is always faster than plain mpn_mul_n (or a
      41      future mpn_mulhi) for the range we will be called.  Follow up that
      42      assumption.
      43  
      44    * Decrease scratch usage.
      45  
      46    * Consider removing the residue canonicalisation.
      47  */
      48  
      49  void
      50  mpn_redc_n (mp_ptr rp, mp_ptr up, mp_srcptr mp, mp_size_t n, mp_srcptr ip)
      51  {
      52    mp_ptr xp, yp, scratch;
      53    mp_limb_t cy;
      54    mp_size_t rn;
      55    TMP_DECL;
      56    TMP_MARK;
      57  
      58    ASSERT (n > 8);
      59  
      60    rn = mpn_mulmod_bnm1_next_size (n);
      61  
      62    scratch = TMP_ALLOC_LIMBS (n + rn + mpn_mulmod_bnm1_itch (rn, n, n));
      63  
      64    xp = scratch;
      65    mpn_mullo_n (xp, up, ip, n);
      66  
      67    yp = scratch + n;
      68    mpn_mulmod_bnm1 (yp, rn, xp, n, mp, n, scratch + n + rn);
      69  
      70    ASSERT_ALWAYS (2 * n > rn);				/* could handle this */
      71  
      72    cy = mpn_sub_n (yp + rn, yp, up, 2*n - rn);		/* undo wrap around */
      73    MPN_DECR_U (yp + 2*n - rn, rn, cy);
      74  
      75    cy = mpn_sub_n (rp, up + n, yp + n, n);
      76    if (cy != 0)
      77      mpn_add_n (rp, rp, mp, n);
      78  
      79    TMP_FREE;
      80  }