contrib/gmp/mpz/tdiv_q_2exp.c

   1 /* mpz_tdiv_q_2exp -- Divide an integer by 2**CNT.  Round the quotient
   2    towards -infinity.
   3
   4 Copyright 1991, 1993, 1994, 1996, 2001, 2002 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 the GNU Lesser General Public License as published by
  10 the Free Software Foundation; either version 3 of the License, or (at your
  11 option) any later version.
  12
  13 The GNU MP Library is distributed in the hope that it will be useful, but
  14 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  15 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  16 License for more details.
  17
  18 You should have received a copy of the GNU Lesser General Public License
  19 along with the GNU MP Library.  If not, see http://www.gnu.org/licenses/.  */
  20
  21 #include "gmp.h"
  22 #include "gmp-impl.h"
  23
  24 void
  25 mpz_tdiv_q_2exp (mpz_ptr w, mpz_srcptr u, mp_bitcnt_t cnt)
  26 {
  27   mp_size_t usize, wsize;
  28   mp_size_t limb_cnt;
  29
  30   usize = u->_mp_size;
  31   limb_cnt = cnt / GMP_NUMB_BITS;
  32   wsize = ABS (usize) - limb_cnt;
  33   if (wsize <= 0)
  34     w->_mp_size = 0;
  35   else
  36     {
  37       mp_ptr wp;
  38       mp_srcptr up;
  39
  40       if (w->_mp_alloc < wsize)
  41         _mpz_realloc (w, wsize);
  42
  43       wp = w->_mp_d;
  44       up = u->_mp_d;
  45
  46       cnt %= GMP_NUMB_BITS;
  47       if (cnt != 0)
  48         {
  49           mpn_rshift (wp, up + limb_cnt, wsize, cnt);
  50           wsize -= wp[wsize - 1] == 0;
  51         }
  52       else
  53         {
  54           MPN_COPY_INCR (wp, up + limb_cnt, wsize);
  55         }
  56
  57       w->_mp_size = usize >= 0 ? wsize : -wsize;
  58     }
  59 }