1  /* mpz_cdiv_q_2exp, mpz_fdiv_q_2exp -- quotient from mpz divided by 2^n.
       2  
       3  Copyright 1991, 1993, 1994, 1996, 1998, 1999, 2001, 2002, 2004, 2012,
       4  2015 Free Software Foundation, Inc.
       5  
       6  This file is part of the GNU MP Library.
       7  
       8  The GNU MP Library is free software; you can redistribute it and/or modify
       9  it under the terms of either:
      10  
      11    * the GNU Lesser General Public License as published by the Free
      12      Software Foundation; either version 3 of the License, or (at your
      13      option) any later version.
      14  
      15  or
      16  
      17    * the GNU General Public License as published by the Free Software
      18      Foundation; either version 2 of the License, or (at your option) any
      19      later version.
      20  
      21  or both in parallel, as here.
      22  
      23  The GNU MP Library is distributed in the hope that it will be useful, but
      24  WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
      25  or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
      26  for more details.
      27  
      28  You should have received copies of the GNU General Public License and the
      29  GNU Lesser General Public License along with the GNU MP Library.  If not,
      30  see https://www.gnu.org/licenses/.  */
      31  
      32  #include "gmp-impl.h"
      33  
      34  
      35  /* dir==1 for ceil, dir==-1 for floor */
      36  
      37  static void __gmpz_cfdiv_q_2exp (REGPARM_3_1 (mpz_ptr, mpz_srcptr, mp_bitcnt_t, int)) REGPARM_ATTR (1);
      38  #define cfdiv_q_2exp(w,u,cnt,dir)  __gmpz_cfdiv_q_2exp (REGPARM_3_1 (w,u,cnt,dir))
      39  
      40  REGPARM_ATTR (1) static void
      41  cfdiv_q_2exp (mpz_ptr w, mpz_srcptr u, mp_bitcnt_t cnt, int dir)
      42  {
      43    mp_size_t  wsize, usize, abs_usize, limb_cnt, i;
      44    mp_srcptr  up;
      45    mp_ptr     wp;
      46    mp_limb_t  round, rmask;
      47  
      48    usize = SIZ (u);
      49    abs_usize = ABS (usize);
      50    limb_cnt = cnt / GMP_NUMB_BITS;
      51    wsize = abs_usize - limb_cnt;
      52    if (wsize <= 0)
      53      {
      54        /* u < 2**cnt, so result 1, 0 or -1 according to rounding */
      55        MPZ_NEWALLOC (w, 1)[0] = 1;
      56        SIZ(w) = (usize == 0 || (usize ^ dir) < 0 ? 0 : dir);
      57        return;
      58      }
      59  
      60    /* +1 limb to allow for mpn_add_1 below */
      61    wp = MPZ_REALLOC (w, wsize+1);
      62  
      63    /* Check for rounding if direction matches u sign.
      64       Set round if we're skipping non-zero limbs.  */
      65    up = PTR(u);
      66    round = 0;
      67    rmask = ((usize ^ dir) >= 0 ? MP_LIMB_T_MAX : 0);
      68    if (rmask != 0)
      69      for (i = 0; i < limb_cnt && round == 0; i++)
      70        round = up[i];
      71  
      72    cnt %= GMP_NUMB_BITS;
      73    if (cnt != 0)
      74      {
      75        round |= rmask & mpn_rshift (wp, up + limb_cnt, wsize, cnt);
      76        wsize -= (wp[wsize - 1] == 0);
      77      }
      78    else
      79      MPN_COPY_INCR (wp, up + limb_cnt, wsize);
      80  
      81    if (round != 0)
      82      {
      83        if (wsize != 0)
      84  	{
      85  	  mp_limb_t cy;
      86  	  cy = mpn_add_1 (wp, wp, wsize, CNST_LIMB(1));
      87  	  wp[wsize] = cy;
      88  	  wsize += cy;
      89  	}
      90        else
      91  	{
      92  	  /* We shifted something to zero.  */
      93  	  wp[0] = 1;
      94  	  wsize = 1;
      95  	}
      96      }
      97    SIZ(w) = (usize >= 0 ? wsize : -wsize);
      98  }
      99  
     100  
     101  void
     102  mpz_cdiv_q_2exp (mpz_ptr w, mpz_srcptr u, mp_bitcnt_t cnt)
     103  {
     104    cfdiv_q_2exp (w, u, cnt, 1);
     105  }
     106  
     107  void
     108  mpz_fdiv_q_2exp (mpz_ptr w, mpz_srcptr u, mp_bitcnt_t cnt)
     109  {
     110    cfdiv_q_2exp (w, u, cnt, -1);
     111  }