source/libs/gmp/gmp-src/mpn/generic/dcpi1_bdiv_q.c

   1 /* mpn_dcpi1_bdiv_q -- divide-and-conquer Hensel division with precomputed
   2    inverse, returning quotient.
   3
   4    Contributed to the GNU project by Niels Möller and Torbjorn Granlund.
   5
   6    THE FUNCTIONS IN THIS FILE ARE INTERNAL WITH MUTABLE INTERFACES.  IT IS ONLY
   7    SAFE TO REACH THEM THROUGH DOCUMENTED INTERFACES.  IN FACT, IT IS ALMOST
   8    GUARANTEED THAT THEY WILL CHANGE OR DISAPPEAR IN A FUTURE GMP RELEASE.
   9
  10 Copyright 2006, 2007, 2009-2011 Free Software Foundation, Inc.
  11
  12 This file is part of the GNU MP Library.
  13
  14 The GNU MP Library is free software; you can redistribute it and/or modify
  15 it under the terms of either:
  16
  17   * the GNU Lesser General Public License as published by the Free
  18     Software Foundation; either version 3 of the License, or (at your
  19     option) any later version.
  20
  21 or
  22
  23   * the GNU General Public License as published by the Free Software
  24     Foundation; either version 2 of the License, or (at your option) any
  25     later version.
  26
  27 or both in parallel, as here.
  28
  29 The GNU MP Library is distributed in the hope that it will be useful, but
  30 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  31 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  32 for more details.
  33
  34 You should have received copies of the GNU General Public License and the
  35 GNU Lesser General Public License along with the GNU MP Library.  If not,
  36 see https://www.gnu.org/licenses/.  */
  37
  38 #include "gmp.h"
  39 #include "gmp-impl.h"
  40
  41
  42 mp_size_t
  43 mpn_dcpi1_bdiv_q_n_itch (mp_size_t n)
  44 {
  45   /* NOTE: Depends on mullo_n interface */
  46   return n;
  47 }
  48
  49 /* Computes Q = N / D mod B^n, destroys N.
  50
  51    N = {np,n}
  52    D = {dp,n}
  53 */
  54
  55 void
  56 mpn_dcpi1_bdiv_q_n (mp_ptr qp,
  57                     mp_ptr np, mp_srcptr dp, mp_size_t n,
  58                     mp_limb_t dinv, mp_ptr tp)
  59 {
  60   while (ABOVE_THRESHOLD (n, DC_BDIV_Q_THRESHOLD))
  61     {
  62       mp_size_t lo, hi;
  63       mp_limb_t cy;
  64
  65       lo = n >> 1;                      /* floor(n/2) */
  66       hi = n - lo;                      /* ceil(n/2) */
  67
  68       cy = mpn_dcpi1_bdiv_qr_n (qp, np, dp, lo, dinv, tp);
  69
  70       mpn_mullo_n (tp, qp, dp + hi, lo);
  71       mpn_sub_n (np + hi, np + hi, tp, lo);
  72
  73       if (lo < hi)
  74         {
  75           cy += mpn_submul_1 (np + lo, qp, lo, dp[lo]);
  76           np[n - 1] -= cy;
  77         }
  78       qp += lo;
  79       np += lo;
  80       n -= lo;
  81     }
  82   mpn_sbpi1_bdiv_q (qp, np, n, dp, n, dinv);
  83 }
  84
  85 /* Computes Q = N / D mod B^nn, destroys N.
  86
  87    N = {np,nn}
  88    D = {dp,dn}
  89 */
  90
  91 void
  92 mpn_dcpi1_bdiv_q (mp_ptr qp,
  93                   mp_ptr np, mp_size_t nn,
  94                   mp_srcptr dp, mp_size_t dn,
  95                   mp_limb_t dinv)
  96 {
  97   mp_size_t qn;
  98   mp_limb_t cy;
  99   mp_ptr tp;
 100   TMP_DECL;
 101
 102   TMP_MARK;
 103
 104   ASSERT (dn >= 2);
 105   ASSERT (nn - dn >= 0);
 106   ASSERT (dp[0] & 1);
 107
 108   tp = TMP_SALLOC_LIMBS (dn);
 109
 110   qn = nn;
 111
 112   if (qn > dn)
 113     {
 114       /* Reduce qn mod dn in a super-efficient manner.  */
 115       do
 116         qn -= dn;
 117       while (qn > dn);
 118
 119       /* Perform the typically smaller block first.  */
 120       if (BELOW_THRESHOLD (qn, DC_BDIV_QR_THRESHOLD))
 121         cy = mpn_sbpi1_bdiv_qr (qp, np, 2 * qn, dp, qn, dinv);
 122       else
 123         cy = mpn_dcpi1_bdiv_qr_n (qp, np, dp, qn, dinv, tp);
 124
 125       if (qn != dn)
 126         {
 127           if (qn > dn - qn)
 128             mpn_mul (tp, qp, qn, dp + qn, dn - qn);
 129           else
 130             mpn_mul (tp, dp + qn, dn - qn, qp, qn);
 131           mpn_incr_u (tp + qn, cy);
 132
 133           mpn_sub (np + qn, np + qn, nn - qn, tp, dn);
 134           cy = 0;
 135         }
 136
 137       np += qn;
 138       qp += qn;
 139
 140       qn = nn - qn;
 141       while (qn > dn)
 142         {
 143           mpn_sub_1 (np + dn, np + dn, qn - dn, cy);
 144           cy = mpn_dcpi1_bdiv_qr_n (qp, np, dp, dn, dinv, tp);
 145           qp += dn;
 146           np += dn;
 147           qn -= dn;
 148         }
 149       mpn_dcpi1_bdiv_q_n (qp, np, dp, dn, dinv, tp);
 150     }
 151   else
 152     {
 153       if (BELOW_THRESHOLD (qn, DC_BDIV_Q_THRESHOLD))
 154         mpn_sbpi1_bdiv_q (qp, np, qn, dp, qn, dinv);
 155       else
 156         mpn_dcpi1_bdiv_q_n (qp, np, dp, qn, dinv, tp);
 157     }
 158
 159   TMP_FREE;
 160 }