Home | History | Annotate | Line # | Download | only in generic
dcpi1_bdiv_q.c revision 1.1.1.1 
      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 Mller 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, 2010 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 the GNU Lesser General Public License as published by
     16 the Free Software Foundation; either version 3 of the License, or (at your
     17 option) any later version.
     18 
     19 The GNU MP Library is distributed in the hope that it will be useful, but
     20 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
     21 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
     22 License for more details.
     23 
     24 You should have received a copy of the GNU Lesser General Public License
     25 along with the GNU MP Library.  If not, see http://www.gnu.org/licenses/.  */
     26 
     27 #include "gmp.h"
     28 #include "gmp-impl.h"
     29 
     30 
     31 
     32 mp_size_t
     33 mpn_dcpi1_bdiv_q_n_itch (mp_size_t n)
     34 {
     35   /* NOTE: Depends on mullo_n interface */
     36   return n;
     37 }
     38 
     39 /* Computes Q = N / D mod B^n, destroys N.
     40 
     41    N = {np,n}
     42    D = {dp,n}
     43 */
     44 
     45 void
     46 mpn_dcpi1_bdiv_q_n (mp_ptr qp,
     47 		    mp_ptr np, mp_srcptr dp, mp_size_t n,
     48 		    mp_limb_t dinv, mp_ptr tp)
     49 {
     50   while (ABOVE_THRESHOLD (n, DC_BDIV_Q_THRESHOLD))
     51     {
     52       mp_size_t lo, hi;
     53       mp_limb_t cy;
     54 
     55       lo = n >> 1;			/* floor(n/2) */
     56       hi = n - lo;			/* ceil(n/2) */
     57 
     58       cy = mpn_dcpi1_bdiv_qr_n (qp, np, dp, lo, dinv, tp);
     59 
     60       mpn_mullo_n (tp, qp, dp + hi, lo);
     61       mpn_sub_n (np + hi, np + hi, tp, lo);
     62 
     63       if (lo < hi)
     64 	{
     65 	  cy += mpn_submul_1 (np + lo, qp, lo, dp[lo]);
     66 	  np[n - 1] -= cy;
     67 	}
     68       qp += lo;
     69       np += lo;
     70       n -= lo;
     71     }
     72   mpn_sbpi1_bdiv_q (qp, np, n, dp, n, dinv);
     73 }
     74 
     75 /* Computes Q = N / D mod B^nn, destroys N.
     76 
     77    N = {np,nn}
     78    D = {dp,dn}
     79 */
     80 
     81 void
     82 mpn_dcpi1_bdiv_q (mp_ptr qp,
     83 		  mp_ptr np, mp_size_t nn,
     84 		  mp_srcptr dp, mp_size_t dn,
     85 		  mp_limb_t dinv)
     86 {
     87   mp_size_t qn;
     88   mp_limb_t cy;
     89   mp_ptr tp;
     90   TMP_DECL;
     91 
     92   TMP_MARK;
     93 
     94   ASSERT (dn >= 2);
     95   ASSERT (nn - dn >= 0);
     96   ASSERT (dp[0] & 1);
     97 
     98   tp = TMP_SALLOC_LIMBS (dn);
     99 
    100   qn = nn;
    101 
    102   if (qn > dn)
    103     {
    104       /* Reduce qn mod dn in a super-efficient manner.  */
    105       do
    106 	qn -= dn;
    107       while (qn > dn);
    108 
    109       /* Perform the typically smaller block first.  */
    110       if (BELOW_THRESHOLD (qn, DC_BDIV_QR_THRESHOLD))
    111 	cy = mpn_sbpi1_bdiv_qr (qp, np, 2 * qn, dp, qn, dinv);
    112       else
    113 	cy = mpn_dcpi1_bdiv_qr_n (qp, np, dp, qn, dinv, tp);
    114 
    115       if (qn != dn)
    116 	{
    117 	  if (qn > dn - qn)
    118 	    mpn_mul (tp, qp, qn, dp + qn, dn - qn);
    119 	  else
    120 	    mpn_mul (tp, dp + qn, dn - qn, qp, qn);
    121 	  mpn_incr_u (tp + qn, cy);
    122 
    123 	  mpn_sub (np + qn, np + qn, nn - qn, tp, dn);
    124 	  cy = 0;
    125 	}
    126 
    127       np += qn;
    128       qp += qn;
    129 
    130       qn = nn - qn;
    131       while (qn > dn)
    132 	{
    133 	  mpn_sub_1 (np + dn, np + dn, qn, cy);
    134 	  cy = mpn_dcpi1_bdiv_qr_n (qp, np, dp, dn, dinv, tp);
    135 	  qp += dn;
    136 	  np += dn;
    137 	  qn -= dn;
    138 	}
    139       mpn_dcpi1_bdiv_q_n (qp, np, dp, dn, dinv, tp);
    140     }
    141   else
    142     {
    143       if (BELOW_THRESHOLD (qn, DC_BDIV_Q_THRESHOLD))
    144 	mpn_sbpi1_bdiv_q (qp, np, qn, dp, qn, dinv);
    145       else
    146 	mpn_dcpi1_bdiv_q_n (qp, np, dp, qn, dinv, tp);
    147     }
    148 
    149   TMP_FREE;
    150 }
    151